The SCA Water Quality Handbook

Transcription

1 A Specialty Coffee Association Handbook The SCA Water Quality Handbook Part One: A Systematic Guide to Water Fundamentals Edition No. 2

2 Table of Contents Introduction...4 The Specialty Coffee Association (SCA) is a membership-based association built on foundations of openness, inclusivity, and the power of shared knowledge. From coffee farmers to baristas and roasters, our membership spans the globe, encompassing every element of the coffee value chain. SCA acts as a unifying force within the specialty coffee industry and works to make coffee better by raising standards worldwide through a collaborative and progressive approach. Dedicated to building an industry that is fair, sustainable, and nurturing for all, SCA draws on years of insights and inspiration from the specialty coffee community. Part I: SCA Water Chart Why Water Matters How Do We Measure Water Composition? How Minerals Get Into Water How to Characterize a Water s Composition Total Hardness and Alkalinity Other Water Content Measurement Methods Conversion of Hardness and Alkalinity Units Natural Water Compositions What is the Optimum Water Composition That We Need to Aim For? Optimal Composition: Technical Perspective Optimal Water Composition: Sensory Perspective How Do We Treat Water? Treatment Methods Choice of Water Treatment Based on Starting Composition Mixing Different Waters Combining Different Treatment Methods Outlook...37 Note: No part of this report may be reproduced or published in any form including but not limited to print, photocopy, or electronic form without the written permission of the Specialty Coffee Association Specialty Coffee Association, 2018 Part II: Water Fundamentals Water Itself Understanding and Applying ph Units of Concentration Units of Hardness Water, Hardness and Scale Water and Carbon Dioxide Carbonate Cycle: Why Scale and Carbon Dioxide are Relatives Treatment of Hard Water by Decarbonization Electrical Conductivity and TDS...54

3 The Specialty Coffee Association (SCA) is a membership-based association built on foundations of openness, inclusivity, and the power of shared knowledge. From coffee farmers to baristas and roasters, our membership spans the globe, encompassing every element of the coffee value chain. SCA acts as a unifying force within the specialty coffee industry and works to make coffee better by raising standards worldwide through a collaborative and progressive approach. Dedicated to building an industry that is fair, sustainable, and nurturing for all, SCA draws on years of insights and inspiration from the specialty coffee community. Part III: Practical Guide on Handling Water How to Measure Your Water Measuring Total Hardness and Alkalinity Measuring Electrical Conductivity and TDS Achieving Your Desired Water Composition When to Choose Which Treatment Using Reverse Osmosis to Increase the Mineral Content of Water Mixing Two Waters: Choosing Total Hardness or Alkalinity Mixing Three Waters: Choosing Total Hardness and Alkalinity Conversion of Total Hardness and Alkalinity Between Different Concentration Units Conversion Among Different Hardness Degrees for Total Hardness and Alkalinity Converting Hardness and Alkalinity to Other Ions Creating Individualized Water Composition by Adding Salts and Acids Tracking the State of Your Water Treatment in Everyday Operation Conclusion and Recommendations...74 Glossary of Terms...77 References...82 Dr. Marco Wellinger Research Associate, Coffee Excellence Center, Zurich University of Applied Sciences Dr. Samo Smrke Research Associate, Coffee Excellence Center, Zurich University of Applied Sciences Note: No part of this report may be reproduced or published in any form including but not limited to print, photocopy, or electronic form without the written permission of the Specialty Coffee Association Specialty Coffee Association, 2018 Prof. Dr. Chahan Yeretzian Head of the Coffee Excellence Center, Zurich University of Applied Sciences Member of the Board of Directors of the SCA and Chair of the SCA Research Advisory Council Member of the Board of the ASIC - Association for the Science and Information on Coffee Acknowledgements The research was initiated and funded by the SCA and Coffee Excellence Center, Zurich University of Applied Sciences (ZHAW). Enormous thanks goes to Antony Watson for improving the structure, copyediting and proofreading of this handbook.

4 4 Introduction We know that specialty coffee depends on a myriad of factors that all influence overall flavor. A multitude of variables such as variety, terroir, processing method, roast degree, grind size, temperature, brew method and extraction time all play a part in the sensory profile of the cup. As the main constituent of brewed coffee is water, the rest being the mass of extracted soluble brewed solids, the quality of water and its ability to carry flavor potential can truly mean the difference between a good and great coffee. Therefore, the more we understand about the chemical and mineral composition of the water that we are using, the more we are equipped to bring out the best flavor potential in our brew. This revised SCA Water Quality Handbook, featuring the water chart and practical guide sets out to establish a solid scientific framework for a unified and transparent consensus on how we measure, aim and treat water for coffee. The fulcrum of this discussion revolves particularly around the two core parameters of alkalinity and total hardness. In particular, we will explore the suitability of different water treatments by deepening our understanding around total hardness as a crucially important parameter in the proper extraction of coffee. Drawing on recent published research and experiments conducted by the Coffee Excellence Center at Zurich University of Applied Sciences (ZHAW), this handbook serves to promote a spirited exchange of ideas about the water we use for brewing within the specialty coffee community. An updated practical guide and Glossary of terms also offers the user a toolbox of concepts and methods with the aim of making coffee better in the domestic or commercial environment.

5 5 In summary, we seek to bring clarity to three simple, yet fundamental, questions: Measure: What is the chemical composition of my water, and how do I measure it? Aim: Treat: What am I aiming to change, and what are the existing recommendations with regard to sensory and technical considerations? Now that I have decided where I want to go, how do I choose an appropriate water treatment to get me there? It is important to bear in mind that while the approach to the measurement and treatment of our water is based on objective considerations, aiming for the right water type is largely subjective as it is dependent on sensory preference. To address this, recommendations are proposed as to where to aim for the optimum balance in the cup. Part one of the handbook covers the main concepts underpinning the SCA Water Chart. By applying these concepts, users will be able to measure their starting composition of water, determine the target composition, and choose the appropriate treatment methods. The second part of this handbook provides an overview of some of the fundamentals in water science that underpin these key concepts. In this part, we will explore the fundamentals and why they are aimed at users who have either very high alkalinity water (i.e. above 300 ppm CaCO 3 ) or very low alkalinity water (i.e. below 50 ppm CaCO 3 ), or those that want to reduce alkalinity selectively though methods such as dealkalization. This is essential for ensuring a safe and economically viable operation of your coffee equipment - espresso machines in particular. The fundamentals outlined in part two also provide insights into some of the main concepts in water science, namely the phenomena of ph, formation of carbonic acid, and the important role of carbon dioxide under extraction. Part three is a practical guide that covers the type of quality control maintenance needed to make sure a water s total hardness and alkalinity content stays within prescribed parameters. A Glossary of terms is also provided at the end of this handbook to expand on key concepts and definitions.

6 6 Finally, it is important to note that this revised handbook combines some of the key concepts featured in previous resources with the updated water chart and practical guide. The expressed intention for this handbook is to lay the foundation for a clear and transparent consensus around water treatment for coffee, while at the same time, setting the stage for a forthcoming water handbook that will include more detailed insights into sensory impact. It is anticipated that part two of this SCA Water Handbook will be published in the coming years. Dr. Marco Wellinger Research Associate, Coffee Excellence Center, Zurich University of Applied Sciences Dr. Samo Smrke Research Associate, Coffee Excellence Center, Zurich University of Applied Sciences Prof. Dr. Chahan Yeretzian Head of the Coffee Excellence Center, Zurich University of Applied Sciences Member of the Board of Directors of the SCA and Chair of the SCA Research Advisory Council Member of the Board of the ASIC - Association for the Science and Information on Coffee

7 7 PART I: SCA WATER CHART 1 Why Water Matters Other than being essential to all life on Earth, if there is one thing that the specialty coffee community can agree on, it is that good quality water is essential for brewing great coffee. But how do we transform problematic water into high quality water that brings out the best our coffee has to offer, while keeping our equipment in good working order? In the past, water treatment has focused primarily on keeping our espresso machines and water boilers in good condition. While this aims to increase the longevity and safe operation of our equipment, as well as lowering maintenance costs, it can still be ineffective if the correct treatment is not employed. Even with the right treatment, many of today s espresso machines can still break down due to scale build up leading to blockages, or in rarer cases, corrosion. Proper water treatment is therefore a necessity for any economically viable operation. Aside from equipment maintenance, there is also the important consideration of flavor and aroma. If the water being used for extraction is unsuitable, it can mask a coffee s full flavor potential. For example, in dilute coffee brewing preparations such as filter coffee, poor water can overpower a coffee s acidity, leaving the brew dull and lifeless. Given recent advancements in coffee processing, storage, roasting, and extraction, there is now a need to work towards a common consensus on individually crafted water treatment strategies so that we can bring out the full potential of each coffee. In order to achieve this, the SCA Water Chart presented in this handbook should be regarded as a tool in which dial in the correct water using total hardness and alkalinity as key parameters.

8 8 In particular, the water chart defines and clarifies the concepts of total hardness and alkalinity, while creating a foundation for a productive and transparent communication around the application of water for coffee. While the chart only depicts two out of almost a dozen relevant parameters of water composition, it encompasses the most crucial drivers for proper coffee extraction. Therefore, the chart provides a framework to equip users with the ability to measure their water composition at a given location, aim for the chosen composition, and subsequently apply a specific method to treat the water in order to reach the target composition for optimum extraction. The sensory impact of how we correctly aim for an appropriate water type is described here in general terms and it is important to note that this a highly subjective issue. It is acknowledged that there is currently not enough data available to describe in greater detail the effects of total hardness and alkalinity of water on aroma and flavor of coffee, considering the wide range of different coffee origins and varieties, roasting styles, and extraction techniques. Hence, rather than being a definitive reference on which exact composition is most suited for coffee and coffee extraction, the water chart aims to provide a solid framework that can be used and developed by the specialty coffee community. While the general characteristics of water quality apply equally to espresso and filter coffee, the range of recommendations for total hardness and alkalinity can differ significantly. This is why it is equally important to take brew ratio, defined as coffee dose to beverage weight, into account. In an effort to establish a common ground for coffee brewing preparations, we anticipate a ratio of 1:2 for espresso and a 1:15 ratio for filter as a starting point that will affect optimal water characteristics. Please note that the concept of total hardness oversimplifies the relationship of calcium and magnesium ions with regard to their impact on flavor, as well as other potential ions that may be introduced by specific water treatment techniques such as a softener. Nevertheless, calculating the total hardness is still useful. By using this calculation, we can predict the general effects of water on flavor and formulate a direction for choosing an appropriate water treatment. It is widely accepted that discussing the complexity and diversity of the

9 9 properties of water always presents a great challenge. This is because water has so many different interconnected phenomena happening simultaneously at once. To the backdrop of the never-ending cascade of facts about water, this handbook offers a unified framework in which to provide perspective. It should serve as a useful reference for coffee professionals in putting the pieces of the puzzle together so that we can, as a community, make sense of the science - as it relates to total hardness and alkalinity as primary drivers in coffee extraction. 2 How Do We Measure Water Composition? The descriptions that underpin the graphs featured in this handbook focus on the first type of concentration units, specifically traditional hardness units such as ppm CaCO 3. The reason that traditional hardness units are used is twofold. Firstly, it helps to simplify the comparison of different water compositions with respect to their suitability for coffee extraction. Secondly, it simplifies the understanding of technically relevant processes such as scale formation and water treatment. In essence, there are two fundamentally different approaches for characterizing a water type s composition. These are: Mass Concentrations: The concentration of ions is described as mass per volume (e.g. mg/l) as this is the standard for the bottled water method. This approach is only useful for the comparison of concentrations with stated daily intake limits or toxicological thresholds. In other words, concentrations of trace metals that can occur in contaminated groundwater, or old piping such as lead. Given that calcium, magnesium and hydrogen carbonate all have different conversion factors from mass concentrations to the effective number of ions, they can be troublesome for calculating total hardness or alkalinity.

10 10 Amount Concentrations: The concentration of ions, or other elementary entities such as molecules or atoms, is given in units proportional to the actual number of ions per volume. For example, this can be expressed as molar units or charge equivalent units (e.g. ppm CaCO 3 ), sometimes called American degree ( a), in which the ions enter the water by dissolution, and react in an ion-exchanger or exit the water by forming scale. A more detailed explanation on the origin and use of different units of concentration is outlined in a Glossary of terms (see Appendix). 2.1 How Minerals Get Into Water Although water comprises of a large variety of different substances as a result of the Earth s water cycle, water vapor in the atmosphere is essentially pure H 2 O. However, as soon as water starts to condense and form droplets it starts to take up carbon dioxide, which in conjunction with water forms carbonic acid (see Equation 1 below). This process makes the water slightly acidic, so rainwater typically has a ph of 5.7 or below. Equation 1: CO 2(dissolved) + H 2 O (liquid) H 2 CO 3 The acidic rainwater that comes into contact with carbonate rock (e.g. CaCO 3, MgCO 3, or a combination of both), dissolves part of it and acquires magnesium, calcium and hydrogen carbonate ions (HCO 3 - ). In contrast to this, acidic rainwater will barely dissolve any silicate rock such as feldspar or quartz, since theses minerals are much more resistant to dissolution from a process called weathering. The amount of dissolved minerals present in water is not only dependent on the mineral composition, but also on the amount of time water has been in contact with the minerals. Additionally, the particle size of the minerals influences the speed of dissolution and thereby the resulting amount of dissolved minerals in water. As smaller particles of bedrock have a larger surface area, they will dissolve more at a faster rate, thereby increasing the concentration of dissolved solids. Groundwater is considered harder than water found in rivers and lakes because it has generally been in contact with minerals for a longer period. The impact of carbon dioxide on water and its effect on ph is explored in further detail in Chapter 9.

11 How to Characterize a Water s Composition Figure 1 shows one of the most common descriptions used by water treatment specialists or chemists investigating water compositions. It gives an overview of the complete composition of water and is divided into three major sections. On the left-hand side, all ions are separated into the positive ions (i.e. cations) in the upper part and negative ions (i.e. anions) in the lower part. In this depiction, the two bars of positive and negative ions are always of equal size; this is because water always has to meet charge neutrality. In other words, the amount of positive charges from cations has to be equal to the amount of negative charges from anions. To be more precise, this equality in size is due to the choice of unit. For example, any equivalent unit is based on the number of ions, multiplied by their charge, and not based on their mass. The middle part of the graph shows dissolved gases, in this case carbon dioxide and its aquatic twin - carbonic acid. Finally, the right-hand section shows uncharged components of water, namely silicates or organic compounds. In most cases, these make up only a minor part of the total concentration of dissolved solids in water. Figure 1: Overall composition of water The ph of most tap water types is strongly influenced by excess dissolved CO 2 in the range of 5-20 mg/l (Puckorius and Brooke, 1991). Meanwhile, atmospheric water only contains about 0.4 mg/l of dissolved CO 2 regardless of ph and alkalinity. This means that most tap water will increase by approximately one ph unit when left standing in an open container for a day, less if it is stirred, or if it is heated up.

12 Total Hardness and Alkalinity When it comes to analyzing water for espresso machines, the maximum amount of scale that can form is usually the primary consideration. Fortunately, the concepts developed with regard to scale formation are also helpful when applied to coffee extraction. The water chart therefore focuses on two main parameters: Total hardness: This is defined as the sum of calcium and magnesium in equivalent concentrations, or molar concentrations. In rare cases, other ions can contribute to total hardness such as strontium (SMWW, 2012; DIN, 1986; ASTM, 2002; EPA, 1999). Alkalinity = Acid buffer capacity: The amount of acid that has to be added to a water sample to decrease ph to 4.3. Therefore, alkalinity should be regarded as the attenuating effect of adding acid to water, also called neutralizing or buffering. Figure 2 gives a representation of two different water compositions. The left panel represents the overall composition for the vast majority of tap waters. The chart shows that these water types have a total hardness that is higher than its alkalinity. This water composition is also the reason why the term carbonate hardness is often misleading when synonymously used in relation to alkalinity. In other words, carbonate hardness effectively corresponds to the maximum amount of scale that can form and is therefore equal to whichever of the two values of total hardness and alkalinity is lower. The right panel demonstrates this distinction between alkalinity and carbonate hardness with water compositions that have a higher alkalinity than total hardness. Here, carbonate hardness does not equal alkalinity but instead equates to total hardness. This is simply because total hardness is now the limiting factor for the maximum amount of scale that can form. This type of composition can occur, for example, in regions where salt water intrudes into the ground water or when water that has been treated by a softener (i.e. exchanging calcium and magnesium ions for sodium or potassium ions).

13 13 Figure 2: Total hardness, alkalinity and carbonate hardness. Beside the terms used here, there are also a number of other synonyms used. These are: Total hardness = general hardness. Carbonate hardness = temporary hardness. Non-carbonate hardness = permanent hardness. Not hard carbonate is sometimes referred to as apparent carbonate hardness. Please see Chapter 8, which explores the concept of total hardness in depth and Chapter 12.1, where the measurement methods for total hardness and alkalinity are described.

14 Other Water Content There are regions in the world that have significant amounts of other ions besides the ones that we have already highlighted. These ions make local water unsuitable for use in coffee extraction. A couple of examples of this are iron, which causes very noticeable flavor defects in coffee extraction, and lead, which is toxic. There are however specialized treatments to remove these components from water. Of the treatments explored in this booklet, only reverse osmosis and deionization are capable of completely removing them from a given water supply. Some regions also have a high content of gypsum in the bedrock, which can cause scale formation of a different kind other than the familiar build-up of calcium carbonate. Chlorine or chloramines used for disinfection also impart a strongly unpleasant flavor in the resulting brew and should be removed. This is most commonly done by activated carbon filtration systems (see Chapter 4.2). 2.5 Measurement Methods Given that clean water is free of particulates and off-flavors, a sample can be sufficiently characterized for its use in coffee extraction by the measurement of total hardness and alkalinity. The only exception is water with a very high alkalinity (i.e. above 300 ppm CaCO 3 ) or extremely soft (i.e. below 50 ppm CaCO 3 ). In both cases, a ph measurement of the water is advised to avoid damage to equipment. Outside of chemistry labs, total hardness and alkalinity are most practically measured by a method called titration. Total hardness is often measured with complexometric titration using Ethylenediaminetetraacetic Acid (EDTA). Measuring alkalinity can be achieved through a neutralization titration method using a strong acid such as Hydrochloric Acid (HCl). In practice, this means that a solution is added drop-by-drop to a specified amount of water until a color change occurs (e.g. from green to red). Titration kits are available from water treatment suppliers and aquarium stores. A recommended minimum resolution is 20 ppm CaCO 3, or if expressed in German hardness degrees, 1 d.

15 15 Although total hardness and alkalinity are measured by different reactions, both methods result in a measurement value that is proportional to the number of ions. This, in practical terms, is in hardness units rather than mass concentrations. A simple increase of the amount of water used can improve the resolution, or precision, of the measurement. For example, if the measurement states that one drop equals 20 ppm CaCO 3 at a sample volume of 10 ml, conducting the same measurement with 20 ml of water results in one drop equaling 10 ppm CaCO 3. Please note that alkalinity test kits are often incorrectly marketed as 'carbonate hardness' test kits. (see Chapter 11.1) Another very common method of analyzing water composition is to measure electrical conductivity and then estimate the total dissolved solids (TDS) in water from this measurement. Using electrical conductivity, or TDS, to describe water properties is not a meaningful parameter on its own with regard to coffee extraction. This is because the conversion from electrical conductivity to TDS depends heavily on the water composition and temperature, yielding results that can vary significantly. Additionally, even if the estimated TDS value is accurate, it does not contain any information on what the actual composition of TDS is. Conductivity meters, or so-called TDS-meters, are very useful for checking for the stability of the tap water as well as the treated water (see Chapter 11.2). 2.6 Conversion of Hardness and Alkalinity Units Table 1 below provides an overview of the conversion factors for the most common concentration units in water analysis. All values have been calculated based on the IUPAC Periodic Table of the Elements (2013) and the basic definitions of the different hardness degrees. The values are in agreement with Hem (1985) and the DIN norm on water hardness (1986). The charts used in this booklet are all given in units of 'ppm CaCO 3 ' but they can all be easily converted to any of the other traditional hardness units such as d, f or e. Please note that in contrast to mass concentration, the conversion factor for calcium, magnesium, and hydrogen carbonate are identical from one traditional hardness unit to the other. A more detailed step-by-step guide on how to conduct the conversion can be found in Chapters 12.5 and 12.6.

16 16 Table 1: Conversion factors for units of hardness and alkalinity rounded to four significant digits the most common conversion factors are highlighted in grey. ppm CaCO3 d f gpg US e Ca2 + + Mg 2+ (mmol/l) HCO3 - (mmol/l) Ca 2+ (mg/l) Mg 2+ (mg/l) HCO3 - (mg/l) ppm CaCo3 (=mg CaCo3/L) 1 ppm CaCO3 = German degrees ( d) 1 dh = French degrees ( f) 1 fh = Grains per US gallon (gpg) 1 gpg = English degree ( e) 1 e = Ca2 + + Mg2 + (mmol/l) 1 mmol/l = HCO3 - (mmol/l) 1 mmol/l = Ca 2+ (mg/l) 1 mg/l = Mg 2+ (mg/l) 1 mg/l = Please note that English degrees are just another name for the unit described as degrees Clark and grains per imperial gallon (see Glossary). For quick mental arithmetic, the following conversion between the two most common hardness units can be useful and very accurate (i.e. < 2% error). To convert a value in ppm CaCO 3 to d, divide by 20 and then add ten percent. Conversely, to convert a value in d to ppm CaCO 3, multiply by 20 and then subtract ten percent.

17 Natural Water Compositions Now that we have introduced the concepts of total hardness and alkalinity, we can use the SCA Water Chart to easily compare and depict different water compositions. For example, we can do this for any of the traditional hardness units using equally scaled axes starting from zero. Figure 3 shows more than 2000 waters from domestic wells in the US, and examples of bottled water compositions. Most waters group along the diagonal dotted black line where total hardness equals alkalinity. A closer look reveals that most values are not exactly clustered on the diagonal line but are slightly higher in total hardness than alkalinity. The diagonal line in both graphs represent the dissolution of pure calcium (CaCO 3 ) or magnesium carbonate (MgCO 3 ). The small vertical offset is caused by small amounts of chloride or sulfate, which will increase the total hardness without affecting alkalinity. In contrast, a larger offset is almost exclusively due to high sulfate content from gypsum (CaSO 4 ). An example of this is shown in the right-hand graph, depicting the composition of a number of bottled waters. In the example of Cristallo Still, we can see that the water has a very high total hardness of 820 ppm CaCO 3 as compared to a medium alkalinity content of 210 ppm CaCO 3. This large difference is due to significant content of gypsum water resulting in a high hardness and a high sulfate content of 6.24 mmol/l - or 600 mg/l - as stated on the bottle label. The waters that are located below the diagonal have a significant content of sodium that explains the difference between total hardness and alkalinity. This is caused by the intrusion of salt water that contains high concentrations of sodium and hydrogen carbonate, formerly called bicarbonate. Adding sodium and hydrogen carbonate to water increases its alkalinity but total hardness is unaffected, thereby pushing a water composition to the right and away from the diagonal that depicts parity between total hardness and alkalinity. Even though only hardness and alkalinity are depicted in the water chart, almost all certain water characteristics such as significant concentrations of sulfate or sodium can be recognized and even estimated quite accurately. For example, Chapter 12.7 shows a conversion table for water treatment involving the introduction and exchange of other ions into water. For water that contains significant amounts of salts other than calcium or magnesium carbonate, conductivity also has to be taken into account to reduce the risk of corrosion (see Chapter 3.1).

18 18 Figure 3: Sample water compositions: Left panel; 2300 water compositions from domestic wells in the US (De Simone, 2009). Right panel; compositions of bottled water. Meanwhile, Figure 4 summarizes the effect of mineral dissolution in a water s composition and thereby its location within the water chart. The arrow pointing diagonally up and to the right represents the dissolution of pure carbonate rock (e.g. limestone, dolomite). The vertically oriented arrow represents the dissolution of minerals containing chlorides or sulfates, and magnesium or calcium (CaSO 4, MgSO 4, CaCl 2, and MgCl 2 ), thereby increasing total hardness only and resulting in an offset upwards from the diagonal. Finally, the horizontally oriented arrow represents the introduction of sodium and hydrogen carbonate, which most commonly occurs with salt-water intrusion, increasing alkalinity only that results in an offset to the right of the diagonal.

19 19 Figure 4: Interpreting a water composition based on its location on the water chart.

20 20 3 What is the Optimum Water Composition That We Need To Aim For? After clarifying how to characterize a water s composition and thereby determining the initial position on the SCA Water Chart for a given water, this Chapter summarizes recommendations for optimal water composition. Please note that the heritage SCAE Core Zone is given as the recommendation for the optimal water composition for coffee, combining both technical and sensory considerations. There are two main perspectives to define an optimal water composition: Technical: This aims to minimize maintenance and thereby reduce repair or replacement costs, as well as downtime due to a defect or break down of espresso machines and/or brew boilers. Sensory: This perspective aims to bring out the best flavor and aroma of a coffee by modifying the content of total hardness and alkalinity. From a hygiene standpoint, water should also be free of off-flavors due to iron, dissolved chlorine compounds such as chlorine (Cl 2 ), hypochlorite (OCl - ), chloramines, and organic matter in order to avoid unpleasant odors and taste. In the case of chlorine compounds and organic matter, these can be easily addressed by active carbon filtration, which efficiently reduces both. Low levels of iron can be removed by an ion-exchanger (e.g. softeners or decarbonizers), but for higher levels, a more elaborate treatment involving aeration (i.e. bubbling air through the water) and subsequent removal by filtering away the iron particles that form through oxidation.

21 21 The most important aspects that define the optimum water composition from a technical perspective are: Corrosion: Caused by low levels of alkalinity below 40 ppm CaCO 3 (also indicated by low electrical conductivity), ph < 6 or ph > 8, and high concentrations of chlorides, sulfates or nitrates (i.e. more than 80% of the alkalinity in equivalent concentrations). Scale formation: Caused by high levels of hardness and alkalinity that lead to the scaling of boilers and machines, which in turn lead to: Decrease in efficiency of heat transfer, and; Clogging of valves and jets especially in the hot water sections. Figure 5 illustrates the maximum amount of scale that can form at 95 C and 130 C at 1.7 bar steam pressure. The calculations are based on a modified version of the Langelier scaling index (see Glossary) in combination with the use of an equilibrium ph based on alkalinity, and typical dissolved carbon dioxide concentrations (Puckorius and Brooke, 1991; Schulman, 2002). Figure 5: Maximum amount of scale formation at 95 C (left) and 130 C (right).

22 22 The areas that indicate 30, 100 and 200 mg/l of scale can be transformed to absolute amounts by estimating the water throughput by the number of beverages prepared. For example, at 100 beverages per day and 0.1 L per beverage including flushing, the lines correspond to 110 g, 365 g and 730 g of scale that can form per year. In high throughput situations, the water does not stay heated long enough for the all of the scale to form. In contrast, when letting the machine stand for hours in a heated condition, the indicated amounts are accurate. 3.1 Optimal Composition: Technical Perspective Figure 6 illustrates the risk zones where corrosion is likely to occur. The horizontally striped zone marks too high concentrations of chloride or sulfates, which correspond to a Larson-Skold-Index above 0.8 (see Glossary). Although the index is estimated from total hardness and alkalinity alone, it yields a useful result unless high concentrations of sodium are present or introduced with sodium hydrogen carbonate. Other than measuring concentrations of calcium or magnesium carbonate, a more general rule that also encompasses water types with a significant amount of salt has been established. This is based on findings from Lockhart s (1955) research and data from 23 waters close to Barcelona representative of salt water influenced tap waters. To keep the risk of corrosion low, the electrical conductivity (i.e. in units of µs/cm) should be no more than three times the alkalinity in ppm CaCO 3. Furthermore, if we consider the ratio of electrical conductivity to alkalinity, a ratio of 1:3 corresponds to a value of approximately 0.8 of the S1 corrosion index (DIN 12502). The S1 corrosion index (see Glossary) is almost identical to the Larson-Skold index but also takes into account the concentration of nitrates in addition to chloride and sulfate. The small diagonally striped zone marks a range where alkalinity is too low (i.e. < 40 ppm CaCO 3 ) to act as an efficient buffer. Overall, the two zones highlighted in Figures 5 and 6 combined represent risk zones, from a technical perspective.

23 23 Figure 6: Corrosion risk zones. 3.2 Optimal Water Composition: Sensory Perspective When aiming for an optimum water composition from a sensory perspective, the most important aspects to consider are: Influence of total hardness on extraction efficiency: Higher total hardness is assumed to increase extraction efficiency (Hendon et al., 2014). In laboratory tests, this effect could not be verified by means of a coffee refractometer, although a clear impact on flavor balance and aroma was detected. Influence of alkalinity on perceived acidity: The higher the alkalinity, the lower the perceived acidity. Moreover, for high alkalinity (i.e. > 100 ppm CaCO 3 ) the neutralization of acids extracted from coffee by hydrogen carbonate, forms large amounts of carbon dioxide. This can increase extraction time and thereby lead to over extraction (Gardner, 1958; Fond 1995; Navarini and Rivetti 2010).

24 24 This effect is also more pronounced if increased concentrations of sodium are present (Gardner, 1958). Figure 7 summarizes existing recommendations (Leeb and Rogalla, 2006; Rao, 2008; Colonna-D. and Hendon 2015; SCAA, 2009) for optimal water composition for extraction from a sensory perspective. It is important to note that the recommended range for optimum hardness varies widely: Lowest suggested optimum is 51 ppm CaCO 3 (2016 World Brewers Cup). Highest suggested optimum is 175 ppm CaCO 3. (Colonna-Dashwood and Hendon s Water for Coffee). In contrast to this, the recommended range for alkalinity is much smaller: Lowest suggested optimum is 40 ppm CaCO 3. Highest suggested optimum is 75 ppm CaCO 3 (this applies only for total hardness values in the range of ppm CaCO 3 ). While most of these recommendations are aimed at espresso extraction, they can also be applied to brewed coffee. As a general rule, brewed coffee needs less alkalinity for an optimum extraction because much more water is used in comparison to espresso - or in other words, the brew ratio is much higher. Total hardness has less of an impact than alkalinity and also water with high total hardness can yield a high-quality filter brew. For cupping, some professionals prefer to use even softer water in the range of 5-10 ppm CaCO 3 of total hardness and alkalinity. While this practice reportedly did not cause corrosion in water kettles, it is strongly advised against using a water with such a low alkalinity for espresso machines since even small amounts of dissolved carbon dioxide could make this water acidic (i.e. ph < 6) and cause corrosion (see Chapter 9.2).

25 25 Figure 7: Existing recommendations on water compositions. The recommended heritage SCAE Core Zone for espresso machines and brew boilers is illustrated in Figure 8. This graph combines technical aspects to enable a safe operation while taking into account sensory considerations that result in a high-quality brew. The lower left and upper border area of the core zone is shaped by the technical thresholds for corrosion prevention, and to the right, by the maximum scale formation of 30 mg/l in a steam boiler at 130 C, or 12 mg/l in a brew boiler of an espresso machine. The lower border of the core zone recommendation is based on Colonna-Dashwood and Hendon s line of minimal recommended total hardness and alkalinity.

26 26 Figure 8: SCA core zone as recommendation for espresso machines and hot water boilers.

27 27 4 How Do We Treat Water? This Chapter explores how different water treatment methods impact on total hardness and alkalinity. Considerations about ph are also mentioned, although this is restricted to very hard water and the decarbonization method. Since most tap waters in central Europe and the US have total hardness and alkalinity levels that are too high for proper coffee extraction, this of huge for the specialty coffee community as a whole. 4.1 Treatment Methods The most common treatment methods for these waters are aimed at reducing the total hardness or alkalinity, or both. Figure 9 shows the impact of the four main treatment methods that can be used to reduce either total hardness or alkalinity.

28 28 Figure 9: Impact of treatment methods that reduce total hardness or alkalinity, or both. Softener: The upper left graph shows the impact of a softener (S), one of the most common treatment methods. A softener is essentially an ion-exchange method where calcium and magnesium ions are exchanged for either sodium or potassium ions. This treatment reduces total hardness without affecting alkalinity and is therefore directing downward on the water chart.

29 29 Decarbonizer: The upper right graph shows the impact of a decarbonizer (DC), probably the second most common treatment method for coffee applications. As with the softener, decarbonization is also an ion-exchange method. Although in contrast to the former, the calcium and magnesium ions are exchanged for protons (H + ). The released protons in turn neutralize hydrogen carbonate by the formation of carbonic acid. When using this type of treatment, it is essential to maintain some alkalinity because the water can turn acidic and become corrosive. Decarbonization leads to a decrease in total hardness and alkalinity of equal amounts and is therefore directed diagonally down, and to the left. Additionally, the buffered decarbonizer is also depicted (DC*), which is a combination of mostly decarbonizer resin combined with a small quantity of softener resin. The small amount of softener resin prevents the ion exchanger from removing all of the alkalinity, and typically leaves a residual alkalinity of approximately 50 ppm CaCO 3. Demineralizer: The lower left graph shows the impact of a demineralizing (DM) treatment, which can be either reverse osmosis (RO) or a deionizer. Reverse osmosis is also among the most commonly used treatment methods. In contrast to the other methods shown, reverse osmosis is based on the use of a semi permeable membrane that allows water molecules to pass through but blocks almost all of its dissolved components. This water, which is essentially pure, is then often mixed with some tap water to increase the mineral contents to suitable levels. By mixing the pure water from the RO system with tap water, any composition between the initial composition and zero total hardness and zero alkalinity sometimes called 'origin' - can be produced. The RO treatment method is therefore directed towards the origin and its direction varies depending on the initial composition, in contrast to the ion-exchange methods. Meanwhile, the deionizer is another method to produce pure water. Unlike reverse osmosis, the deionizer works by exchanging all ions (i.e. with the combination of a cation exchanger and an anion exchanger) rather than employing a semipermeable membrane. Due to the fact that deionizer cartridges have a relatively low capacity compared to softeners of decarbonizers, they are not suitable for high volume commercial environments.

30 30 Dealkalizer: Finally, the lower right graph shows the impact of dealkalization which can be accomplished by an ion-exchanger or by adding a strong acid. As with decarbonization, it is essential to maintain some alkalinity because the water can turn acidic and become corrosive. In the case of low mineral content, treatment methods to increase total hardness and alkalinity can also be used. Figure 10 shows the impact of four different treatment options: Figure 10: Impact of treatment methods that raise total hardness or alkalinity, or both.

31 31 Hardener: The top left graph depicts the impact of a hardener that introduces calcium or magnesium as chloride or sulfate salts (CaSO 4, MgSO 4, CaCl 2, and MgCl 2 ). Like the name suggests, it is essentially the opposite of a softener and is directed upwards. Hardening can be done by the use of mineralization cartridges or by adding calcium or magnesium salts. Carbonizer: The top right graph shows a carbonizer representing the dissolution of magnesium or calcium carbonate. It is directed diagonally, up and to the right, increasing total hardness and alkalinity by equal amounts. Since calcium carbonate is not soluble enough in neutral water only magnesium carbonate can be used efficiently for this purpose. Reverse Osmosis: As shown in the lower left panel, some RO systems are capable of using the leftover concentrate rather than the pure water that permeates through the membrane. With this system, total hardness and alkalinity of the source water can be increased. The treatment is directed away from the origin and preserves the ratio of total hardness to alkalinity found in the source water. The extent of increase depends on the efficiency of the RO systems but can reach an increase of more than twofold in modern systems (see Chapter 12.2). Alkalizer: Finally, the lower right graph shows the effect of an alkalizer that increases alkalinity only, and therefore is directed to the right. This is accomplished by dissolution of sodium hydrogen carbonate or potassium hydrogen carbonate. A relatively new treatment that is now on the market is the exchange of calcium ions for magnesium ions. This form of ion exchange does not change either total hardness or alkalinity, so both values remain constant. Since calcium and magnesium can affect extraction differently, research into this area has received increased attention recently (Hendon et al., 2014).

32 Choice of Water Treatment Based on Starting Composition Now that we have identified a range of different water treatment methods, let us look at how they can be applied. In essence, all of the water treatment methods fall into one of the following two categories: Continuous or in-line systems: The inlet of the water treatment system is directly connected to the tap water and its outlet to an espresso machine or brew boiler. This system allows for a continuous operation without user assistance. Regular control of the output water is advised to ensure it is stable. Batch or off-line systems: The water is treated as a batch in a tank or other container. Using this system for espresso machines may require the use of an additional pump and accumulator as some pumps need positive pressure at their inlet. While all different types of ion-exchanger and RO can be operated in either of the two modes, the addition of an acid such as a dealkalizer or an alkalizing agent such as sodium hydrogen carbonate are currently not sold as continuous systems in the form of a cartridge or dispenser.

33 33 Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Figure 11: Range of use for treatment methods that reduce total hardness or alkalinity.

34 34 Figure 11 shows the potential range of use for different treatment methods that reduce total hardness or alkalinity in order to arrive at the desired water composition. As mentioned, when using decarbonization or dealkalization, it is essential to retain some alkalinity of at least 40 ppm CaCO 3 in order to avoid corrosive conditions that can break down boilers. Additionally, a decarbonizer is used to treat water with high alkalinity (i.e. > 200 ppm CaCO 3 ) where the formation of carbonic acid can lead to a significant decrease in ph and result in corrosive conditions. These are marked with black and yellow striping in the upper right graph. This can be avoided if the treated water is left to degas its carbonic acid in form of carbon dioxide to the air. Conversely, Figure 12 summarizes the potential range for treatment methods that can be used to increase total hardness or alkalinity. Note that the lower left graph illustrates RO systems, which are capable of using the concentrated water that is usually treated as waste (see Chapter 12.2).

35 35 Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Heritage SCAA Standard Heritage SCAE "Core Zone" for water boilers Figure 12: Range of use for treatment methods that raise total hardness or alkalinity.

36 Mixing Different Waters By mixing water types of different compositions together, virtually any water composition can be produced. The mixture of two waters allows the user to reach any composition on the connecting line illustrated in the left and middle graphs in Figure 13. The mixture of two waters allows the user to reach any composition on the connecting line illustrated in two upper graphs in Figure 13. When mixing three waters, any composition can be achieved within the area of the triangle illustrated in the bottom graph below (see Chapter 12.4): Figure 13: Examples of mixing water with different compositions.

37 Combining Different Treatment Methods In some cases, no single water treatment is capable of changing the initial composition to a desired target. For instance, if the aim is to decrease total hardness and alkalinity but actually increase the difference between the two (i.e. alkalinity is reduced to a larger extent than total hardness), none of the water treatments mentioned can achieve both requirements. In these particular cases, a hybrid treatment using either a decarbonizer combined with a hardener, or a complete demineralization with subsequent remineralization can lead to the target composition. In addition, a combination of complete demineralization and subsequent remineralization can solve problems that arise due to the presence of undesirable ions such as iron (Fe2 + ) or lead (Pb2 + ). 5 Outlook Given that a chosen water source - either from a tap or bottle - can provide hygienic water free of off-flavors such as chlorine, iron or earthy and moldy flavors, this handbook introduces a systematic three-step method for modulating water for optimum coffee extraction. In other words, aiming for a target composition can be determined from measuring the initial composition of a water type before deciding the most crucial step - which is to choose a suitable treatment. The majority of users will find all of the necessary information to decide for a specific water treatment or combination of multiple treatment methods in the preceding Chapters. However, some users will have to dive further into the science of water in order to reach a recommended water composition. Specifically, this concerns the treatment of very high alkalinity water (i.e. above 300 ppm CaCO 3 ), very low alkalinity water (i.e. below 50 ppm CaCO 3 ) or the selective reduction of alkalinity (e.g. dealkalization). These scenarios are discussed in part two on the fundamentals of water.

38 38 Depending on the green beans, roasting style, storage, grinding and extraction method, the actual target composition that leads to the desired outcome will vary significantly. In order to shed light on this, research should include experiments to propose correction factors or alternate optimal zones to account for a number of variables whose influences have not yet been elucidated in detail. Namely, these are: Influence of brew ratio on the optimal composition of water: Recent literature and simple chemical considerations suggest that low brew ratios used for espresso as compared to drip coffee shift the optimum of total hardness and alkalinity to higher values. Influence of temperature and pressure on the optimal values of total hardness and alkalinity: Since temperature and pressure both affect extraction efficiency, this is in turn coupled to the water composition used. Influence of roasting style on the sensory properties of the final beverage: Anecdotal evidence suggests that the use of water with higher concentrations of total hardness and alkalinity can compensate to some extent for a roast that has not been fully developed. Influence of calcium versus magnesium on the extraction and the sensory properties of the final beverage: Theoretical considerations from a recent publication (Hendon et. al, 2014), as well as preliminary experiments, indicate that magnesium has a slightly higher extraction efficiency compared to calcium. The difference between calcium and magnesium with regard to their impact on the sensory properties however remains unclear and is subject to future research. Beside these purely scientific considerations, regional, cultural or individual preferences can also play a significant role in the choice of the optimum water composition. For example, in areas where tap water is very soft (i.e. total hardness and alkalinity are below 40 ppm CaCO 3 ) this might have influenced the development of specific taste preferences and roasting styles.

39 39 PART II: WATER FUNDAMENTALS Water chemistry is a complex subject. At its foundation, it is essentially an unequal marriage of one strongly electron-attracting oxygen atom and two weakly electron-attracting hydrogen atoms. Analogous to a tug-ofwar between unequal partners, the electrons end up being located closer to the oxygen than to the hydrogen atom. This characteristic is called polarity, which refers to the uneven distribution of charge within the water molecule. 6 Water Itself One of the most important consequences of the polar nature of water is that water molecules have a strong tendency to align against each other in a systematic pattern where the oxygen atom of one molecule is located closest to the hydrogen atom of another water molecule. This weak bond is called a hydrogen-bond, which is about one twentieth the strength of the chemical bond between the hydrogen and oxygen at 25 C (CRC, Suresh) illustrated in Figure 14: Figure 14: Hydrogen bond between two water molecules.

40 40 Due to its polar nature, water is a very good solvent for polar compounds such as ionic compounds and polar molecules (e.g. during extraction). Conversely, water hardly dissolves non-polar compounds such as oils and fats, which make up approximately 10 % of the weight of roasted coffee. However, for extraction under high pressure and temperatures for espresso and moka pot, or long contact times like French press, the solubility of nonpolar compounds is significantly increased (Gloess, 2013). Among the many special, anomalous characteristics of water are a number of mostly wellknown phenomena, namely: Water shows two anomalies with regard to its density: Its highest density is reached at 4 C. The density of water as a solid (e.g. ice) is lower than in its liquid form (i.e. water expands during freezing and shrinks when melting). Water has a boiling point that is unusually high and a freezing point that is very low compared to substances made up of similarly small molecules. Water has a very high heat capacity; meaning it takes a lot of energy to heat or cool water. Water is almost incompressible; at a pressure of 1000 bar (i.e. present in the deepest parts of the ocean at 10,000 m below the surface) it is only 5 % more dense than at atmospheric pressure. What is practically more relevant to everyday extraction is that water has a density of almost exactly 1000 kg/m3 or 1 g/ml. This means that 1 g equals 1 ml; 1 kg equals 1 L; and one ton equals 1 m3. The boiling point of pure water is not just determined by its temperature but in fact by the pressure of the surrounding gas phase. For example, the reduced boiling point temperature at high altitudes is a well known phenomena. Figure 15 shows the vapor pressure of water in absolute values, meaning that to calculate overpressure with respect to the atmosphere, such as in a steam boiler, the absolute pressure has to be subtracted by the atmospheric pressure (e.g. approx. 1 bar at sea level).

41 41 Figure 15: Vapor pressure of water as absolute pressure: Equivalent values of atmospheric pressure at different altitudes is indicated on the chart (p < 1 bar), along with static pressure under water (p > 1 bar). 6.1 Understanding and Applying ph By definition, ph is a ratio and therefore dimensionless, or strictly speaking, has a dimension of one. For nearly pure water (i.e. >99.9% equivalent to a TDS < 1000ppm) such as most drinking waters, the ph value can be expressed in a very tangible and precise way: ph 7 denotes that for every half a billion water molecules there is one proton (H + ). It can be stated this way because the proton originates from an ionization reaction in pure water when a water molecule deprotonates to become a hydroxide ion (OH - ) for the same number of water molecules.

42 42 Research shows that when water molecules split off a proton, the free proton is immediately adopted by another water molecule. This phenomenon is called the autodissociation of water and is illustrated in Figure 16: Figure 16: Autodissociation of water: Top; illustrated by the molecular formulas; Bottom; illustrated as ball-andstick model. For the sake of simplicity, this handbook refers to protons (H + ) instead of hydronium ions (H 3 O + ) and ph as a measure for the concentration of free protons (H + ) in water. In practical terms, for every increase of the ph by one unit (+1) the concentration of protons decreases by a factor of ten; and for every decrease of the ph value (-1) the concentration of protons increases by a factor of ten. The opposite, however, holds true for hydroxide ions. The higher the temperature, the more protons - and hydroxide ions - are present in neutral water. Only at 25 C does a neutral ph corresponds to a value of exactly 7 (see Figure 17). Figure 17: Dependence of neutral ph value on temperature.

43 43 Please remember that the acid buffering potential - even as low as 25 ppm CaCO 3 - is 50 times more than the difference in pure acid concentrations between ph5 and ph7. In other words, a water with 25 ppm CaCO3 less alkalinity has 50 times more impact on the beverage acidity than having a starting ph of 5, instead of ph7. It is also important to note that the strength of an acid is measured by its power to transfer its proton to water, thereby using water as a base. Strong acids donate virtually all of their protons when ph levels are below two meaning even if there are already a lot of protons present in the water (i.e. low ph), the acid will still dissociate and donate its proton to the solution. Figure 18 gives examples of everyday liquids across the ph range from highly acidic stomach acid to highly alkaline caustic soda: Substance Stomach acid (empty stomach) Lemon juice Coke Orange and apple juice Skin surface of humans Human saliva Pure water Soap Household ammonia (4% w/w) Concrete Sodium hydroxide (caustic soda) ph-value 1,0 1,5 2,4 2,0 3,0 3,5 5,5 6,5 7,4 7,0 9,0 10,0 11,5 12,6 13,5 14 Type acidic neutral alkaline Figure 18: ph values of everyday products or chemicals.

44 44 7 Units of Concentration In contrast to everyday life where mass and volume are standard units to quantify absolute (e.g. g/l) and relative substance contents (e.g. % w/w, % v/v), chemistry quantifies substances or entities in moles which is a value proportional to the actual number of atoms, ions, or molecules. While using units of mass is common to everyone, they do not reflect the true proportions of the chemical compounds involved in terms of their number of molecules, ions, or atoms. Using units to express the amount of substance concentrations instead of mass concentration is paramount to chemistry. It is important because only the proportions relative to the actual number of entities reflects the ratios needed to understand and explain any chemical process. Amount concentrations, also called molar concentrations, are given as mole per volume or weight, and this is most commonly expressed in water analysis as mmol/l. Derived directly from amount concentrations is the definition of equivalent mass units and hardness degrees, which will be explored further. In contrast to amount concentrations, equivalent concentrations can only be applied to charged ions and are calculated by multiplication of the amount concentration (e.g. mmol/l) by the charge number of the ion (e.g. z ) these are termed as equivalents (e.g. eq where miliequivalents per liter, for example, is abbreviated to meq/l). Figure 19 illustrates the typical composition of a tap water shown in different units.

45 45 Figure 19: Water composition of Zurich tap water (average 2014), illustrating major cations and anion content in drinking water. Left: Mass concentrations (mg/l); Center: Amount concentrations (mmol/l); Right: Charge equivalent concentrations (meq/l = mmol z/l). Since ions constitute typically over 95% of the chemical components (i.e. less than 1% of solutes are uncharged) in fresh water, this limitation is negligible for the purposes of this Chapter. By multiplying the molar concentrations of all ions with their charge, we can calculate the fundamental balance that has to be fulfilled for every water sample to achieve charge neutrality. Measurements and calculations in equivalent units allow for a double entry bookkeeping of water composition, since it allows for an assessment of potential gaps in the analysis. In addition, it is evidently the most transparent and clearest representation when assessing scale formation or water treatment methods. For known water composition, conductivity measurements can be transformed into a value for total dissolved solids (TDS).

46 Units of Hardness It is common in most developed countries to use equivalent units to report hardness. This means that the contents of ionic species (e.g. Mg2 +, Ca2 +, HCO 3 - ) are represented by the equivalent mass of the corresponding solid they could form when precipitating. Furthermore, most hardness equivalent units are defined with respect to the mass of calcium carbonate (e.g. ppm CaCO 3 USA; fh FR; e - UK), except German hardness degrees ( dh) which are defined with respect to calcium oxide. What this means in practice is that the lower of the two such as hardness and HCO 3 - equivalents determine the theoretical maximum mass that can precipitate and form scale, for example in boilers. The maximum amount of scale that can form when water is heated is referred to as carbonate hardness, otherwise known as temporary hardness. In order to determine carbonate hardness, compare total hardness and alkalinity, whichever of the two is lowest determines this. The reason being that both total hardness and alkalinity are needed to form scale. In other words, only one of the two cannot form scale without the other being present. As remarked earlier, these units are not the same as the concentrations featured on bottled water labels that state mass concentrations in mg/l of the respective ions, or neutral molecules such as silicates. Specifically, this means that when one mole of calcium carbonate is removed from water (e.g. scale formation) the concentration of calcium decreases by one mole. Whereas, due to the fundamental rule that a water molecule always stays charge neutral for all processes under consideration in this handbook, the concentration of hydrogen carbonate will decrease by two moles.

47 47 8 Water, Hardness and Scale To understand the different expressions that are used in the industry, it is worth exploring the rationale behind the concept of hardness. The term water hardness originates from the capacity of water to precipitate soaps during washing. The predominant reason for the precipitation of soaps is a high content of calcium and magnesium (SMWW, 2012; DIN, 1986; ASTM, 2002). While other polyvalent cations such as iron, barium and strontium may also precipitate soap, their presence in fresh water is seldom above trace amounts and can therefore be discounted in most circumstances. Additionally, water used in boilers at home or in industrial equipment can become encrusted with scale residues that are being formed mostly from calcium carbonate (CaCO 3 ), and also at high ph (>10) by magnesium hydroxide (Mg(OH) 2 ). Since the scale formation by precipitation of calcium carbonate is equally dependent on the concentration of carbonates as calcium, the concept of carbonate hardness has been introduced and is still very common in the water industry. Most fresh water sources contain an equivalent concentration of hydrogen carbonate (HCO 3 - ) that is lower than total hardness. This imposes a limit on the maximum amount of total hardness that can precipitate. Some calcium and magnesium will also remain in the water. In this case, only a fraction of total hardness (i.e. calcium and magnesium) corresponding to the hydrogen carbonate content is called carbonate hardness - or temporary hardness. The remaining calcium and magnesium content is called non-carbonate hardness or permanent hardness. It is the part of the total hardness that remains, after all HCO 3 and CO has been used up. Non-carbonate hardness is most commonly introduced into the water by sulfate or chloride-minerals that do not form scale (i.e. do not precipitate). In the opposite case that the equivalent hydrogen carbonate concentration is higher than total hardness, the carbonate hardness corresponds to the total hardness as all calcium and magnesium can be precipitated and no permanent hardness remaining. In this case, the fraction of HCO 3 that is higher than total hardness would have to be called, following the hardness logic, as non-hard carbonate (see Figure 2 in Chapter 2.3).

48 48 9 Water and Carbon Dioxide The story of water and coffee is closely linked to the limestone that is dissolved in the ground and the scale it can form in coffee equipment. However, there is also another substance that plays a key role in the water cycle, and therefore coffee extraction - which is carbon dioxide. As outlined earlier, water dissolves carbon dioxide in the atmosphere, which in turn forms carbonic acid and becomes acidic (see Chapter 2.1). Moreover, the plants and microorganisms in the soil release carbon dioxide, which in turn is dissolved in the ground water. This acidic water then goes on to dissolve limestone in the ground to pickup total hardness and alkalinity. For reasons of simplicity, it is customary in water chemistry to combine dissolved carbon dioxide and carbonic acid. For example, the strength of carbonic acid is expressed in relation to the sum of dissolved carbon dioxide and carbonic acid present. Therefore, we will include carbonic acid when talking about the concentration of dissolved carbon dioxide in this handbook. Most tap waters have a value of between ph 6 7 and are therefore close to neutral. It is important to note that this is not because it is pure water, but because the alkalinity picked up by dissolving limestone is balanced by dissolved CO 2. The only practical way to dissolve scale in water in a short timeframe is with carbonized water, containing high concentrations of dissolved carbon dioxide. In order to understand this better, let us first have a look at the solubility of CO 2 along with that of oxygen (O 2 ). Figure 20 shows the solubility of the two gasses depending on temperature; the hotter the water is, the less soluble the two gases become. In addition, the amount of gas that dissolves in water also depends, on how much of the respective gas is present in the air. For example, CO 2 is present in air at only 400 ppm in contrast to oxygen, which is present at 21% (i.e ppm). When describing the solubility of gases in water it is expressed as an equilibrium concentration that is reached if you wait long enough or stir the water vigorously for a couple of minutes.

49 49 Since there is much more oxygen present in the atmosphere, its equilibrium concentration is much higher than that of CO 2. In contrast, when both gases are present at the same concentration in the air the concentration of carbon dioxide is much higher. In fact, inside an espresso basket at 9 bars pressure and 90 C, approximately 4 g of carbon dioxide can dissolve per liter. Figure 20: Solubility of oxygen and carbon dioxide at atmospheric concentrations and at 1 bar. Source: Geng (2010) and CRC handbook (2014). If we take a different perspective on how plants and microorganisms in the soil release carbon dioxide, which in turn is dissolved in the ground water, we can see how this effect leads to a decrease in ph of one unit or more depending on the dissolved carbon dioxide of the water out of the tap. The opposite reaction is degassing of carbon dioxide from water by either letting it stand in an open container, stirring, or heating. Figure 21 shows the evolution of the ph from a tap water containing 180 ppm CaCO 3. Out of the tap, the water measures ph 7.5, which corresponds to 11 mg/l of dissolved carbon dioxide. By stirring it in an open container over the course of a day, it can rise by more than one ph unit. After 24 hours it can measure a value of ph 8.7 which then corresponds to 0.7 mg/l carbon dioxide. This is almost down to the equilibrium level with the atmosphere, which is at 0.4 mg/l at 20 C independent of ph.

50 50 Figure 21: Evolution of ph of a tap water. 9.1 Carbonate Cycle: Why Scale and Carbon Dioxide are Relatives As we explained at the beginning of this Chapter, water droplets in the atmosphere dissolve carbon dioxide, which in turn forms carbonic acid. See the following equation: Equation 2: CO 2(dissolved) + H 2 O H 2 CO 3 The carbonic acid (H 2 CO 3 ), which is formed as a consequence of the dissolution of CO 2 in water is a weak acid and hence donates one of its two protons to water, forming a single-charged hydrogen carbonate, which according to the following equation, leads to an acidification of the water: Equation 3: H 2 CO HCO 3 + H + Hydrogen carbonate is an acid as well, as it may in principle further donate its one proton to water, forming a double-charged carbonate ion (CO ). This is expressed in the following equation: - Equation 4: HCO 3 + CO H +

51 51 Yet under normal circumstances, this is very unlikely to happen, as the proton donating power of hydrogen carbonate is small at ph values that prevail in drinking water. Only in very basic conditions above ph 9 does carbonate form. For example, since carbonic acid (H 2 CO 3 ) is a much weaker acid than sulfuric or nitric acid, the average ph of rainwater in Switzerland has risen from approximately ph 4.5 in 1985 to ph 5.5 in 2013, equaling a decrease of a factor 10 in proton concentration of rainwater. At the current atmospheric concentration levels of CO 2, pure water in equilibrium with the atmosphere has a ph value of approx. 5.7 due to the acidification from carbonic acid (H 2 CO 3 ). Figure 22 shows the different substances that are involved in the carbonate cycle and how they are linked to each other. Whereas the left and center part are occurring naturally, the right part including the decarbonization, is added by water treatment. Figure 22: The carbonate cycle in coffee applications.

52 Treatment of Hard Water by Decarbonization A special case that involves carbon dioxide formation is the treatment of hard water by decarbonization. The working principle of the decarbonizer that reduces total hardness and alkalinity is based on the exchange of magnesium or calcium ions by protons. This means that although the hydrogen carbonate is protonated and therefore not an acid buffer anymore, it is still present in the form of carbonic acid, which in turn is in a constant exchange with dissolved carbon dioxide. If the treatment is done by an inline system where the carbonic acid cannot escape as carbon dioxide, it leads to two effects. Firstly, the ph of the treated water will decrease and in case of a water with a high starting level of total hardness (i.e. > 300 ppm CaCO 3 ), this can effectively make the treated water so acidic that the risk of corrosion increases significantly. Secondly, a large amount of carbonic acid will also lead to excessive crema production during the extraction of espresso. For example, a barista may have an issue with the espresso being very foamy resulting in large bubbles that collapse quickly in the crema. This is because a decarbonizer is being used to treat a very hard water (i.e. above 300 ppm CaCO 3 ). The reduction of approximately 250 ppm CaCO 3 in alkalinity increased the dissolved carbon dioxide by 220 mg/l in the form of carbonic acid. For a standard double espresso recipe with a 1:2 brew ratio, this means that even for a very fresh coffee one hour after roast and two minutes after grinding, the water can add another 50 % to the carbon dioxide already contained in the coffee grounds. Figure 23 illustrates this decrease of ph depending on the alkalinity reduction by decarbonization.

53 53 Figure 23: Decrease in ph due to dissolved carbon dioxide from decarbonization. It is also worth noting that when using a decarbonizer, every reduction of 10 ppm CaCO 3 decreases the electrical conductivity by 17 µs/cm (or 30 µs/cm for reduction by 1 d).

54 54 10 Electrical Conductivity and TDS As mentioned in part one of this handbook, the conversion of electrical conductivity (EC) to total dissolved solids (TDS) gives only a rough estimate of the amount of dissolved solids in a water sample, but it does not contain any information on the type of substances. In the actual estimation of TDS, the measurements have a typical error range of +/-30%, and in extreme cases more than a 50% error margin. For this reason, they should not be used as a standalone quality parameter. The reason for this uncertainty, or error, is that the actual conversion factor depends strongly on the exact composition. Moreover, water temperature strongly influences the conversion and most of the cheaper devices on the market do not measure or correct for this. For every 1 C, the conductivity (or TDS) measurement changes by about 2%. This means that a sample at 10 C or at 30, instead of the standard of 20 C, gives a reading that is 20% too high or too low, respectively. Table 2 shows the conversion factors from EC in µs/cm to TDS in mg/l (or equally in ppm) at 20 C for common scale or limestone (i.e. calcium carbonate (CaCO 3 ), magnesium carbonate (MgCO 3 ), table salt (sodium chloride (NaCl)), rock salt (potassium chloride (KCl)), gypsum (calcium sulfate (CaSO 4 )), epsom salt (magnesium sulfate (MgSO 4 )), calcium chloride (CaCl 2 ) and magnesium chloride (MgCl 2 )). Whereas for pure scale, EC is almost equal to TDS; for table salt and rock salt, TDS is less than half of EC. Table 2: Conversion factor from EC to TDS for the most commonly found dissolved solids in water. CaCO3 MgCO3 NaCl KCl CaSO4 MgSO4 CaCl2 MgCl2 NaHCO3 KHCO3 TDS (mg/l) / EC (µs/ cm) at 20 C

55 55 Table 3 gives examples for conversion factors from EC (in µs/cm) to TDS (in mg/l) for major US cities. Data on mineral composition was taken from Lockhart (1955) and Pawlowicz (2008). Compared to the commonly used standard of 0.7 in mg/l of TDS per 1 µs/cm of electrical conductivity, most tap waters are close to the standard while some read up to 27% higher (e.g. Chicago at 0.89) or 25% lower (e.g. Galveston at 0.52). Table 3: Examples for conversion factor from EC to TDS for the major US cities (Lockhart, 1955). Boston San Francisco Pittsburgh St. Louis New York Cleveland Chicago Los Angeles Sarasota Indianapolis Kansas City Galveston TDS (mg/l) / EC (µs/cm) at 20 C PART III: PRACTICAL GUIDE ON HANDLING WATER This practical guide should be used as an aid to go through the threestep process of how to measure, aim and treat, as described in part one. A prerequisite to using this handbook is to start with a clean and hygienic water that is safe for consumption. The first step gives you instructions on what, and how, to measure. The second step provides solutions on how to get a specific composition by using either water treatment, mixing of different waters or by adding specific salts or acids to achieve the targeted composition. Finally, the third step gives examples to achieve a chosen water composition in the everyday operation of your café, roastery, laboratory or business or at home.

56 56 11 How to Measure Your Water Unfortunately, water is far too complex to write a short guide that works for every water type used. However, based on data from central Europe and the USA the vast majority of tap waters can be sufficiently characterized by measuring three parameters: Total hardness Alkalinity Conductivity The following Chapter gives descriptions on how to use test kits and measurement instruments so that the user can achieve a reliable result. Let us start with measuring the most important and useful characteristic of your water - total hardness and alkalinity Measuring Total Hardness and Alkalinity Outside of a well-equipped analytical laboratory, total hardness and alkalinity can be measured by a method called titration. It is important to note that most manufacturers of water titration kits available from water treatment suppliers or aquarium stores still use incorrect labelling. Therefore, a test measuring carbonate hardness is in fact measuring alkalinity. See Chapter 2.3 for more details on the distinction between alkalinity and carbonate hardness. Titration is done by adding a test solution to a water sample, counting the number of drops needed to get a specified change in color. Total hardness and alkalinity each have a different test solution and the tests are conducted separately. The first step is to fill the test tube with a specified amount of water, most commonly this is 5 ml. Next, the respective solution is added drop-by-drop, making sure to mix the sample well by shaking after the addition of each drop. The first drop results in the clear water sample taking on a color.

57 57 For total hardness, this is most often green and for alkalinity, this is most often blue. If the color is barely visible, meaning the water sample stays almost transparent, then this indicates that the concentration of the respective parameter is very low. If this is the case, try holding the test tube over a piece of white paper to make sure the color is more easily determined. The color intensity is also more visible if you look down through the tube over the white paper. In order to determine the correct measurement value, keep on adding drops until the color starts to change. Once the color has changed completely your measurement is finished and the number of drops can be converted to a reading of total hardness or alkalinity. For instance, a first slight color change might occur in hardness test kits when the color starts to change from red to red with a hue of green. This means that your final value has not been reached yet. Keep on adding and counting the drops until the water is completely green and any red color has disappeared. The minimum recommended resolution is 20 ppm CaCO 3 (or 1 d). Most tests also include the conversion formulas to different hardness units (see Chapter 12.5). IIn Figure 24, the different steps in a titration for total hardness are shown. Figure 24: Different stages of using a total hardness titration kit. Left: Water sample is ready for the titration test; Center: First drops have been added and the solution has turned green; Right: Final stage of the measurement has been reached since the solution has turned completely to red.

58 58 When measuring treated water with values of total hardness and alkalinity below 100 ppm CaCO 3, titration measurement can be imprecise. This is because the accuracy is +/- 1 drop, equaling 20 ppm CaCO 3. To avoid this, simply double the water volume in the test tube (e.g. 10 ml instead of 5 ml). This now means that one drop equals half the previous indication of 10 ppm CaCO 3. For even more precision you can triple the water amount, which increases the sensitivity by a factor of three, meaning one step equals 6.7 ppm CaCO 3. The downside of using more water is that you are going to use more of your test solution and mixing the sample will become more difficult as the amount is increased. If the test vial does not feature additional volume indications, the simplest way of doing this is to weigh the amount with a scale using the conversion of 1 g = 1 ml which introduces only a negligible error (i.e. <0.5% at temperatures below 30 C). If your solution does not take on the specified color listed in your test manual or description outlined here and turns yellow-brown instead of green, your test kit might be faulty because it is too old, was exposed to light or exposed to too high temperatures Measuring Electrical Conductivity and TDS Measuring electrical conductivity is nothing more than holding a measurement device in a sample of water. It is crucial that the sample should have a temperature close to 20 C. This is because EC is strongly dependent on temperature - the lower the temperature the higher the EC. The same goes for TDS-Meters which are essentially an EC meter but with a built-in conversion. The heritage SCAA standard refers to a TDS meter that uses a factor of 0.7, meaning that 1 µs/cm is assumed equal to 1 mg/l or 1 ppm. One of the caveats when using a TDS meter is that there is a significant share of meters that use a factor of 0.5 or use a variable conversion factor. Therefore, it is best to make sure what conversion factor a specific meter uses by consulting the user manual or device specifications.

59 59 Figure 25: A conductivity meter that also measures temperature.

60 60 12 Achieving Your Desired Water Composition In this Chapter, four different approaches are presented so that you can get a water with exactly the composition you are aiming for. An understanding of the basic concepts described in the water chart in part one is important to fully understanding the following three main recommendations for treating your water: Adopting standard methods available by water treatment companies. Mixing different waters to get the desired composition. Creating a specific water composition by taking pure water and add salts When to Choose Which Treatment The water composition you wish to target heavily depends on the type of extraction method. When preparing filter coffee, a lot more water is used than in espresso (e.g. 1:15 for filter compared to 1:2 for espresso). This is why the potential to reduce acidity is much higher in filter coffee, as there is much more water per coffee dose than for espresso. Consequently, one can leave the alkalinity at much higher values for espresso (up to 150 ppm CaCO 3 ), before a significant buffering effect on the acidity will become apparent. Of course, leaving the alkalinity at a higher value also increases the amount of scale formation. Although the actual amount of scale formation is also ph dependent, it is worth bearing in mind that the lower the ph the less scale forms. In terms of risk management, this means that espresso machines are not suitable for risky experiments due to their high commercial value. In contrast, water kettles for filter coffee are low cost and can be used with water having a higher risk of scale formation or corrosion risk.

61 61 In the case of limestone dominated water with an alkalinity concentration equal to, or almost 70 ppm CaCO 3 lower than the concentration of total hardness, a decarbonizer is the best option for most applications. However, for espresso machines and water boilers the following recommendations should be followed: Up to 250 ppm CaCO 3 alkalinity: Set the bypass valve on your decarbonizer cartridge so that the output water has an alkalinity of ppm CaCO 3. For water with more than 250 ppm CaCO 3 alkalinity: Set the bypass valve on your decarbonizer cartridge so the output water the alkalinity will reduce by no more than 200 ppm CaCO 3 (see Chapter 9). For example, when starting with 350 ppm CaCO 3 alkalinity the output water should not be set below 150 ppm CaCO 3 alkalinity. Otherwise an excessive amount of carbonic acid will be formed resulting in a ph drop (e.g. below ph 6) and significantly increase the chance of corrosion. For the use of water in open kettles, decarbonization can be applied without restrictions, since any carbonic acid that is formed during the process will escape to the surrounding air when the water is heated. Reverse osmosis is currently the only reliable treatment method for salt water (e.g. treated sea water) and water where alkalinity is more than 70 ppm CaCO 3 with lower total hardness (e.g. gypsum water), and contains traces of iron, manganese or high sodium content. For home use or small volumes for tests an almost pure water (i.e. water with very low mineral content) can be used to dilute the tap water (e.g. RO water or water with total hardness and alkalinity below 20 ppm CaCO 3 ) Using Reverse Osmosis to Increase the Mineral Content of Water When using reverse osmosis, the maximum degree of concentration that can be achieved is directly correlated with the efficiency (i.e. waste ratio) of the system.

62 62 In other words, the less water is used to produce one liter of permeate, which can be described as almost pure water, the higher the concentration of the leftover. Usually, this leftover concentrate is treated as waste. Although there are several reverse osmosis systems on the market that are capable of using this concentrate as the actual output in order to increase the mineral content of water. This can also be used to increase total hardness and alkalinity if the source water is of low mineral content but otherwise high quality, specifically in the absence of other undesirable or harmful compounds such as metals or chlorine. Table 4 lists the conversion factor to calculate the maximum increase in mineral content of water as a function of the efficiency of a reverse osmosis system. Table 4: Waste ratio and concentration factors for reverse osmosis. Waste / % Ratio of diluted permeate to concentrated leftover Concentration factor Increase in mineral content / % 80 1 : : : : : : : : : : : : :

63 Mixing Two Waters: Choosing Total Hardness or Alkalinity As mentioned earlier in Chapter 4, virtually any water composition can be produced by mixing water types of different compositions together. The following recommendations are designed to prepare waters containing different concentrations of alkalinity and total hardness. Figure 26 shows an example of mixing two waters, where: Water 1 is an almost pure water from reverse osmosis water or bottled water that is very low in total hardness and alkalinity (e.g. 5 ppm CaCO 3 alkalinity / 10 ppm CaCO 3 total hardness (5 10)). Water 2 is a medium hard water containing 150 ppm CaCO 3 alkalinity and 200 ppm CaCO 3 total hardness ( ). Figure 26: Illustration of the mixture of two waters.

64 64 By mixing water 1 and water 2, any point on the line connecting the two compositions can be achieved. A combined impression of varying water composition can be carried out by simply mixing two waters in different ratios with each other. To calculate the percentages of water 1 and 2 in a mixture, a simple equation can be used for any chosen value of alkalinity or total hardness: Choosing a target alkalinity: Share of water 1 = 100* (Alkalinity of water 2 - Target alkalinity) / (Alkalinity of water 2 - Alkalinity of water 1) Share of water 2 = 100 Percentage of water 1 Choosing a target total hardness: Share of water 1 = 100* (Total hardness of water 2 - Target total hardness) / (Total hardness of water 2 - Total hardness of water 1) Share of water 2 = 100 Percentage of water 1 For example, if you choose to target an alkalinity of 60 ppm CaCO 3, the equation is as follows: % water 1= 100*(150-60)/(150-5) = 64.1 % - which then brings the share of water 2 to 35.9 %. Or if you target a total hardness of 120 ppm CaCO 3 the equation becomes: % water 1 = 100*( )/(200-10) = 42.1 % - which then brings the share of water 2 to 57.9 %.

65 Mixing Three Waters: Choosing Total Hardness and Alkalinity If the three waters chosen are different enough, alkalinity and total hardness can be changed independently from each other by mixing these three waters. The downside of this approach is that it complicates the calculation in an equation with 16 mentions of eight different variables. This means that we will achieve total hardness and alkalinity values from all three of the different water used for mixing, as well as the target total hardness and alkalinity. Table 5: Example of three waters used for mixing. Three waters for mixing Alkalinity / PPM CaCO3 Total hardness / ppm CaCO3 Water 1 RO / distilled-like water Water 2 Typical mineral water Water 3 Epsom (MgSO4) concentrate In the example provided, an almost pure water (e.g. Water 1) is used. Water 2 is a typical hard water that contains mostly limestone or scale resulting in high total hardness and alkalinity. Meanwhile, Water 3 is made using Epsom salt, and contains a high total hardness but almost no alkalinity.

66 66 Figure 27 shows the three different waters highlighted in green circles are mapped onto the water chart, which covers the range of compositions that can be achieved. Figure 27: Illustration of the mixing process including the starting waters (Water 1-3) as well as the target water 4 illustrated in Table 6 below.

67 67 For example, Table 6 shows the calculated values for four chosen targets. A guideline on to how to convert total hardness and alkalinity values between different units is detailed in the next Chapter. Table 6: Examples for target waters and the share of the three input waters used to mix them. Chosen target water compositions Alkalinity / ppm CaCO3 Total hardness / ppm CaCO3 Share of water 1 / g*l -1 Share of water 2 / g*l -1 Share of water 3 / g*l -1 Target Target Target Target Conversion of Total Hardness and Alkalinity Between Different Concentration Units Table 7 presents the conversion factors to ppm CaCO 3 from mass concentration units, otherwise known as straight mg/l and for molar units, otherwise known as milimoles per liter (mmol/l). For the conversion from hardness units to mass concentration there is a different factor for all three substances (e.g. calcium, magnesium and hydrogen carbonate) because they all have a different weight. For milimoles per liter, the conversion factor from hardness degrees is identical for calcium and magnesium. In contrast, the conversion factor for hydrogen carbonate is half that due to their different charge.

68 68 Table 7: Conversion factors to ppm CaCO 3. Unit name Conversion factor to ppm CaCO3 Calcium (mg/l) Magnesium (mg/l) Hydrogen carbonate (mg/l) Calcium and Magnesium (mmol/l) Hydrogen carbonate (mmol/l) For example, how do we calculate the total hardness (e.g. sum of calcium and magnesium) and alkalinity of a water with 50 mg/l of calcium, 10 mg/l of magnesium and 100 mg/l of hydrogen carbonate? Total hardness: Alkalinity: 50 x = 125 ppm CaCO3 10 x = 41 ppm CaCO 3 => total hardness is 166 ppm CaCO x = 82 ppm CaCO 3 => alkalinity is 82 ppm CaCO 3

69 Conversion Among Different Hardness Degrees for Total Hardness and Alkalinity Table 8 lists the conversion factors from other hardness degrees to ppm CaCO 3. The conversion factor from one unit to the other (e.g. ppm CaCO 3 to d) is always the same for total hardness and alkalinity. To convert any other unit to ppm CaCO 3, simply multiply the value with the corresponding conversion factor. For example, how do convert a value of 2 d total hardness to ppm CaCO 3? 2 x = 35.7 ppm CaCO 3 To calculate the reverse (i.e. to convert a value in ppm CaCO 3 to any other unit, simply divide it by the conversion factor). How do we convert a value of 50 ppm CaCO 3 alkalinity to e? 50 / = 2.92 e Table 8: Conversion factors from different hardness degrees to ppm CaCO 3. Unit name Conversion factor to ppm CaCO3 German degrees ( d) French degrees ( f) 10 Grains per US gallon (gpg) English degree ( e) 14.25

70 Converting Hardness and Alkalinity to Other Ions The different treatment methods outlined earlier exchange calcium, magnesium, or hydrogen carbonate ions with other ions. Other treatments introduce calcium, magnesium, or hydrogen carbonate ions along with others such as sulfates, chlorides, or sodium ions. In order to calculate how much of these other ions are introduced into the water by a specific treatment, Table 9 below lists the conversion factors. Table 9: Conversion factors of total hardness and alkalinity to other ions. Na2 (mg/l) K + (mg/l) Dissolved CO2 (mg/l) SO42 - (mg/l) CL - (mg/l) Na + (mmol/l) K + (mmol/l) Dissolved CO2 (mmol/l) SO42 - (mmol/l) CL - (mmol/l) ppm CaCo3 (=mg CaCo3/L) 1 ppm CaCO3 = German degrees ( d) 1 dh = French degrees ( f) 1 fh = Grains per US gallon (gpg) 1 gpg = English degree ( e) 1 e = Ca2 + + Mg2 + (mmol/l) 1 mmol/l = HCO3 - (mmol/l) 1 mmol/l = Ca 2+ (mg/l) 1 mg/l = Mg 2+ (mg/l) 1 mg/l = HCO3 - (mg/l) 1 mg/l = Please note that a special case is the production of carbonic acid that forms from dissolved carbon dioxide by the decarbonizer (see Chapter 9).

71 Creating Individualized Water Composition by Adding Salts and Acids Below are step-by-step instructions to help you create a target water composition by adding salts and acids: Alkalizing solution: Prepare the alkalizing solution by dissolving 3 g of baking soda (i.e. pure sodium hydrogen carbonate also called sodium bicarbonate (NaHCO 3 )) in 1 L of RO water. This solution will now contain 100 d of alkalinity. Adding a further 10 g of this solution to 1 L of water will add an additional 1 d of alkalinity. Baking soda can be bought in most supermarkets but make sure that it is pure NaHCO 3 baking powder as many products contain additional ingredients such as cornstarch and other carbonate salts. Hardening solution: Prepare the hardening solution by dissolving a salt containing either calcium or magnesium but no carbonate. In this example, a solution of CaCl 2 combined with MgCl 2 x 6 H 2 O is given. This means that there are six water molecules bound within the crystal structure of the magnesium chloride. Either calcium or magnesium sulfate is advised for espresso machines since chlorides increase the chance of corrosion. Often, espresso machine manufacturers strongly advise against using a water that has significant amounts of chloride (i.e. more than 5 mg/l). Magnesium hardening solution: To prepare, dissolve 7.3 g of the magnesium salt in 1 L of RO water. This solution will now contain 200 d of total hardness. Adding a further 10 g of this solution to 1 L of water will result in an additional 2 d of total hardness. Calcium hardening solution: To prepare, dissolve 4.0 g of CaCl 2 in 1 L of RO water, resulting in a solution containing 200 d of total hardness in the form of calcium.

72 72 Dealkalizing solution: Finally, it is also possible to decrease alkalinity by adding a strong acid. However, since this involves handling a hazardous substance it is not recommended for the chemically untrained user. As this preparation involves potentially dangerous substances, it is absolutely necessary to wear eye protection, gloves and a lab coat when handling concentrated acids. To prepare a solution with an alkalinity of 100 d, add 3 g of concentrated hydrochloric acid (37% m/m) to 1 L of RO water. It is important to pour the concentrated acid into the water and not the other way around. To decrease the alkalinity of 1 L of water by 1 d, add 10 g of the -100 d solution. Please note that the unit of measurement is negative since it decreases the alkalinity of a water when added. 13 Tracking the State of Your Water Treatment in Everyday Operation Depending on available data on the stability of a given water supply, a smaller or larger initial measurement series should be conducted. For water that is from a single groundwater source, a high stability in water composition can be expected over the short and long term. On the other hand, if multiple sources feed into the tap water network, daily and seasonal variations may occur. Therefore, an initial measurement series should be conducted to test both the incoming water composition throughout the day, as well as measuring the changes from one day to the next. In addition, if the tap water source is from shallow groundwater, river or lake, it is worth to looking for seasonal changes in the water composition. Analysis of water can be as simple as using a conductivity meter. However, whether or not this is sufficient depends on the type of treatment chosen and the type of potential fluctuations in tap water composition. For example, a softener will slightly increase the conductivity of the water but, in practice, is not enough to use as a reliable indicator.

73 73 When using a decarbonizer, conductivity is reduced significantly by removing calcium and magnesium and buffering away the alkalinity to form dissolved carbon dioxide. As a gas, CO 2 does not contribute to TDS and almost nothing to conductivity. Figure 28 shows an example for three medium hard tap waters from Switzerland and values for electrical conductivity versus alkalinity. The tap waters located to the upper right are connected by a dotted line with the decarbonized water in the lower left. For pure decarbonization, the electrical conductivity decreases by 1.64 µs/cm for every 1 ppm CaCO 3 decrease in alkalinity. The ratio of decrease in EC per decrease in alkalinity measured is between This is slightly higher but still close to the value 1.64 for decarbonization. The higher steepness is due to a small amount of softening also occurring in treatment cartridges using buffered decarbonization (see Chaoter 4.1). Figure 28: Electrical conductivity (EC) versus alkalinity of three different waters before and after treatment.

74 74 Although the change in conductivity is dependent on the starting composition, EC can be tested on an RO system with a bypass or remineralization, as well as a decarbonizer. Lastly, manufacturers of water treatment product often provide tables to calculate the capacity of their solutions depending on the starting composition and water volume. Therefore, using a rough estimation of the monthly or yearly water use can serve to estimate when the next change in your water treatment system needs to be scheduled. 14 Conclusion and Recommendations This SCA Water Quality Handbook featuring the water chart and practical guide is built on an internationally recognized water standard which will enhance the sensory aspects of coffee brewing, as well as minimizing the risk of damaging to equipment. The findings and recommendations are therefore a forward-looking effort to bring clarity to the debate around water by offering a clear and practical framework for optimizing the treatment of water for coffee extraction. The key points can be summarized as follows: Total hardness, alkalinity, and ph are the three central measures to characterize water*. The most common ions found in water are calcium, magnesium and hydrogen carbonate. Total hardness corresponds to the sum of calcium and magnesium in equivalent units (e.g. d, ppm CaCO 3 etc.). The higher the alkalinity, the lower the acidity of the extracted coffee especially in filter coffee. The lower the values for total hardness and alkalinity are, the less scale can form.

75 75 Alkalinity should be at least 40 ppm CaCO 3 (2.2 d) to ensure that the water is sufficiently buffered to minimize the risk of corrosion. Traditional hardness units (e.g. ppm CaCO 3, d, f) provide an easy and accurate way to assess a water s suitability for use in coffee extraction. With regard to sensory aspects, the acid buffer capacity should be referred to as alkalinity. Note that carbonate hardness is not necessarily the same as alkalinity. Water for coffee extraction should: Be odor free and hygienic. Have a total hardness of between ppm CaCO 3 ( d). Have an alkalinity of between ppm CaCO 3 ( d). Have a ph of between 6 8. Current recommendations for optimal water composition allow for a large variation of optimum total hardness but call for a much smaller variation of alkalinity. Moreover, all current recommendations share the characteristic that total hardness should exceed alkalinity. The majority of water types have an alkalinity that runs slightly lower than its total hardness. As most waters are far too high in alkalinity and also too high in total hardness, water treatment is required. For the majority of waters dominated by calcium or magnesium carbonate, the risk of corrosion can be kept low if alkalinity is at least 40 CaCO 3 between ph 6 8. For other waters containing a significant amount of gypsum (CaSO 4 ) the risk of corrosion can be kept low if total hardness is less than 80% higher than alkalinity. Water with significant amounts of salt as a result of seawater intrusion or salt in the bedrock, electrical conductivity (i.e. in µs/cm) should be no more than three times the alkalinity (i.e. in ppm CaCO 3 ) to reduce the risk of corrosion.

76 76 Carbon dioxide and other related compounds found in water (e.g.carbonic acid, hydrogen carbonate and carbonate ion, and scale) play a central role in water chemistry. These compounds have an impact in the safety and longevity of brewing equipment, as well as aiding coffee extraction. All water treatment techniques can be discussed and compared using the SCA Water Chart. * Except for water containing iron, lead or other unsuitable or toxic compounds in significant amounts.

77 77 Glossary of Terms The following are basic descriptions of the attributes of water in relation to brewing: Acid buffering capacity: The amount of acid that must be added to a water sample to decrease ph to 4.3. Therefore, it is attenuating the effect of adding acid to water, also called neutralizing or buffering. Alkalinity: The ability of the water to neutralize acids. Also describes the concentration of carbonate and bicarbonate compounds in the water. Atom: An electrically neutral, defining structure of a chemical element (e.g. Calcium (Ca)), that cannot be divided into smaller particles by any chemical process. Anion: Negatively charged ion (e.g. Chloride bicarbonate (Cl - )). Brew ratio: Ratio between the weight of a beverage and the weight of coffee used to prepare it. Carbonate hardness: Carbonate hardness effectively corresponds to the maximum amount of scale that can form and is therefore equal to whichever of the two values of total hardness and alkalinity is lower. Synonymous with temporary hardness. Cation: Positively charged ion (e.g. Calcium (Ca² + )). Chemical Bonds: The atoms in molecules and compounds are held together by chemical bonds. In the context of water, the bonds are typically covalent or ionic. H 2 O is held together by a covalent bond, whereas NaCl or CaCO 3 are held together by ionic bonds that will split more easily.

78 78 Chlorine (Cl): Tap water is chlorinated with hypochlorite (Cl 2 ) to kill bacteria and microbes. Not to be confused with chlorides such as sodium chloride (NaCl), calcium chloride (CaCl 2 ), or magnesium chloride (MgCl 2 ). Compound: An electrically neutral group of two or more atoms of the same or different elements, held together by chemical bonds (e.g. Oxygen (O 2 ); Water - two hydrogen atoms bonded to an oxygen atom (H 2 O); or Salt (NaCl). Decarbonizer: Decarbonization is also an ion-exchange method, though in contrast to the former, the calcium and magnesium ions are exchanged for protons (H + ). The released protons in turn neutralize hydrogen carbonate by formation of carbonic acid. Decarbonization leads to a decrease in total hardness and alkalinity by equal amounts. Deionizer: A deionizer produces pure water, by exchanging all ions with a combination of a cation exchanger and an anion exchanger. Because the deionizer cartridges have a relatively low capacity (i.e. the amount of water that can be processed) compared to softeners of decarbonizers, they are not suitable for large volumes. Synonymous with 'demineralizer'. Degrees Clark: A measure for total hardness and alkalinity of water. It is defined as one grain (64.8 g) of calcium carbonate (e.g. scale) per Imperial gallon (4.55 L) of water. Electrical conductivity: Electrical conductivity (EC) measures the ability of a substance to transmit or conduct electricity. Since pure water is a pure conductor, EC in drinking water originates mainly from dissolved ions. Electrical conductivity has often been used to estimate the total dissolved solids content (TDS) of water samples but conversion factors can be up to +/-50%. Grains per imperial gallon: A unit of water hardness defined as 1 grain (64.8 milligrams) of calcium carbonate dissolved in 1 US gallon of water (3.78 L). It translates into 1 part in about 58,000 parts of water or 17.1 parts per million (ppm). Also called Degrees Clark.

79 79 Hardness: Now referred to as 'Total Hardness', this is the concentration of calcium (Ca) and magnesium (Mg) in the water. More calcium and magnesium = harder water. Less calcium and magnesium = softer water. mg/l: Milligrams per liter. It is the equivalent to ppm when testing water at <45ºC. Non-carbonate hardness: The concentration of calcium and magnesium occurring as compounds other than carbonates in the water. Not hard carbonates: The concentration of minerals, other than calcium and magnesium, which occur as carbonate compounds. Permanent hardness: The calcium and magnesium that cannot precipitate from water when boiled. ppm: Parts per million.it is equivalent to mg/l when testing water at <45ºC. ph: This describes whether the water is more acid, more alkaline, or neutral. Molecule: An electrically neutral group of two or more atoms held together by chemical bonds. For example, Oxygen (O 2.) or Water (H 2 O). Ion: Atoms or molecules that have a net positive or negative charge. Langelier scaling index: An approximate indicator of the degree of saturation of calcium carbonate in water. It is calculated using the ph, alkalinity, calcium concentration, total dissolved solids, and water temperature of a water sample collected at the tap. Larson-Skold-Index: A measure for the corrosivity of water towards steel. It is calculated by dividing the sum of chloride and sulfate by alkalinity.

80 80 Mass concentration: The concentration of ions is given as mass per volume, such as mg/l, is standard for bottled water. This method is only useful for comparison of concentrations with stated daily intake limits or toxicological thresholds (e.g. for trace metals that can occur in contaminated groundwater or old piping such as lead). Since calcium, magnesium and hydrogen carbonate all have different conversion factors from mass concentrations to number of ions, they are unnecessarily troublesome for calculating total hardness or alkalinity. Non-carbonate hardness: Difference between total hardness and alkalinity, only present for water with a total hardness higher than alkalinity. Synonymous with 'permanent hardness'. Reverse Osmosis (RO): Reverse osmosis is based on the use of a semipermeable membrane that allows water molecules to pass through but blocks almost all of its dissolved components resulting in water which is essentially pure. Often, some tap water is mixed back into the almost pure RO water to increase the mineral contents to suitable levels. By mixing the pure water from the RO system with tap water, any composition between the initial composition and pure water, at zero total hardness and zero alkalinity, can be produced. S1 corrosion index: A measure for the corrosivity of water towards steel. In comparison to the Larson-Skold-Index, it also takes into account the concentration of nitrates. Sodium (Na): Alkali metal that can occur as a chloride compound (e.g. Salt (NaCl)), or as a carbonate compound in water. Softener: A softener is an ion-exchange method where calcium and magnesium ions are exchanged for either sodium or potassium ions. This treatment reduces total hardness without affecting alkalinity. Temporary hardness: The calcium and/or magnesium can precipitate from the water when boiled, and form scale deposits.

81 81 Total hardness: Defined as the sum of calcium and magnesium in equivalent concentrations (or molar concentrations). In rare cases, other ions can contribute to total hardness, for example strontium. TDS: Total dissolved solids simply means the sum of all solid substances present in the water. For water, this parameter is often estimated by electrical conductivity by assuming a fixed composition. A conversion factor of 0.7 in mg/l of TDS per 1 µs/cm of electrical conductivity is used by the heritage SCAA Water Standard. In laboratory tests, it is measured by evaporation and weighing of the solid residue also including uncharged dissolved solids such as silicates that do not contribute to electrical conductivity.

82 82 References ASTM D 1067: Standard test methods for acidity or alkalinity of water; Colonna-Dashwood M, Hendon C.; Water for Coffee; self-publication; Bath, UK; CRC handbook of chemistry and physics, Haynes, W.M.; Lide, D.,R.; Bruno, T.J.; 94th edition, Solubility of Selected Gases in Water and Solubility of Carbon Dioxide in Water at Various Temperatures and Pressures. DeSimone, L.A., 2009, Quality of water from domestic wells in principal aquifers of the United States, : U.S. Geological Survey Scientific Investigations Report , 139 p., available online at DIN ; German standard methods for the examination of water, waste water and sludge, Summary indices of actions and substances (Group H), Water hardness (H 6); DIN 12502; Protection of metallic materials against corrosion - Guidance on the assessment of corrosion likelihood in water distribution and storage systems; EPA, United States Environmental Protection Agency; EPA Method 130.2; Hardness, Total (mg/l as CaCO3) (Titrimetric, EDTA); Fond O.; Effect of water and coffee acidity on extraction: Dynamics of coffee bed compaction in espresso type extraction; ASIC, Proceedings of the 16th Colloquium, Kyoto; Gardner, D.G., Effect of certain ion combinations commonly found in potable water on rate of filtration through roasted and ground coffee, Journal of Food Science, 23, pp , Prediction of oxygen solubility in pure water and brines up to high temperatures and pressures GENG, M., DUAN, Z.;Geochimica et Cosmochimica Acta; 74;2010. International Union of Pure and Applied Chemistry (IUPAC); Periodic Table of the Elements; iupac.org/reports/periodic_table; 2013.

83 83 Hem John D.; Study and Interpretation of the Chemical Characteristics of Natural Water, 3rd edition; U.S. geological survey water-supply paper 2254; Hendon C, Colonna-Dashwood L. and Colonna-Dashwood M., The Role of Dissolved Cations in Coffee Extraction, Journal of Agricultural and Food Chemistry; 62 (21), ; Leeb, T., Rogalla, I.; Kaffee, Espresso & Barista; TomTom Verlag; 4th edition; Navarini L., Rivetti D.; Water quality for Espresso coffee; Journal of Food Chemistry; 122, ; Pawlowicz, R.; Calculating the conductivity of natural waters; Journal of Limnology and Oceanography; 6; pp ; Puckorious, P.R.; Brooke, J.M.; A new practical index for calcium carbonate scale prediction in cooling tower systems; Corrosion, the Journal of Science and Engineering; 47 (4); pp ; Rao, S: The professional barista s handbook; self-publication; USA; Schulman, J.; Insanely long water FAQ; 2002; Quality/Water%20FAQ.pdf. SMWW: American Public Health Association, American Water Works Association, Water Environment Federation; Standard Methods for the Examination of Water and Wastewater, 22nd edition; Specialty Coffee Association of America (SCAA); SCAA Standard: Water for Brewing Specialty Coffee; November 21, 2009.

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