COOL HOW TO BE. Cooling Methods and Their Impact From Roast to Cup

Transcription

1 HOW TO BE COOL Cooling Methods and Their Impact From Roast to Cup by Christopher Schooley photos by Nolan Dutton of Ozo Coffee The roasting process has many stages: drying, browning reactions, caramelization, first crack and cell expansion, to name a few. Each stage plays an important part in the development of the flavor profile of the coffee the whole roasting process is development. The stage that begins with the first crack and includes the beginning of caramelization is referred to as the development stage by some roasters, but this can be misleading as it diminishes the importance and the impact of the other stages during roasting. continued on page roast July August

2 One such stage that can be easily overlooked is the cooling stage. While it doesn t happen in the roaster itself, properly cooling the roast has a dramatic impact on the cup. With that thought in mind, at the end of the roast, the coffee has quite a bit of energy and momentum itself, so much so that even when removed from the roasting chamber it s still changing, only now it s doing that food item continues to cook and adds as much as 10 to 15 degrees of internal temperature after being removed from the heat. This may change the development and degree of doneness issue. If you cool it too slowly, the long series chain polymers, sugars, fructose and glucose will find other constituents to link up with in the coffee, and they are not as soluble. Cooling with Air tray, most drum roasters purely use a cooling tray with a perforated bottom. This is connected to a blower that pulls air from the room through the just-roasted coffee as a pivot arm stirs the coffee to create a more The roasting process is an exchange of momentum. Energy is built inside the roasting chamber and then transferred to the coffee as it progresses through the roast. in an uncontrolled environment that is, if the core temperature of the beans is not actively being brought down. In cooking, this is called carry-over. The past the point desired. Without continuing to add energy to the coffee, it will eventually cool; however, the longer it takes to cool to room temperature, the more the coffee Staub is saying that if a coffee takes too long to cool, there s not as much soluble sweetness to draw from when brewed. Through extensive testing done by Staub, as documented in the lecture The most common cooling method used by small-craft coffee roasters is cooling with air. Although some fluid-bed roasters do include a water quench as well as a cooling even cooling for the whole charge. Most roasters view the blower (motordriven impeller to suck or blow large continued on page 42 will continue to change from when the above, by me and by a number of other roast was initially stopped. Delayed roasters and roaster manufacturers cooling may result in an undesirable that I spoke with for this article, it has baked or dried-out character, but been duly noted that getting post-roast generally, sweetness is the most cooling times down to 4 minutes or less notable difference. This is a common provides a noticeable difference in the roasting anecdote, but one that has sweetness of the cup. been demonstrated time and again The difference in cooling from through various trials conducted by between 5 minutes and 4 minutes is so roasters and roaster manufacturers. dramatic that the panel that tasted the coffees in the experiments Staub created The most common cooling method used by small-craft felt the sweetness had increased by at least double by shortening the cooling to less than 4 minutes. Joseph A. Rivera, founder of the online coffee science resource coffeechemistry.com, says that because the soluble/insoluble chemistry described above happened during roasting at temperatures greater than coffee roasters is 400 degrees F, and not during cooling, cooling itself might not be the cause of this greater perception of sweetness. cooling with air. He adds that if rapidly cooled coffees do possess more sweetness, it is more likely due to certain aromatics being preserved by the quicker cooling process. Aromatics are temperature In a lecture on cooling at the SCAA Expo in 2002, Agtron managing partner Carl Staub spoke about the impact of proper cooling on sugar development during the roasting and cooling process: The primary sugar in coffee is sucrose. During the roasting process you fracture the sucrose, and you want to caramelize it or polymerize it in the scientific term. But, you also have to maintain solubility. If it doesn t come out when you put water into it, it is not going to be a sweet cup. Having the sugar there is one issue, and being able to get it out with hot water is another dependent, meaning that when beans are exposed to higher temperatures they will also release more aromatics, some of which may be sweet in character and ultimately lost in the cup, Rivera says. One concern about cooling is fracturing the cells. According to Stephan Diedrich of Diedrich Manufacturing, in order to fracture the cells the coffee would have to be cooled almost instantly, which would take a great deal of resources to remove the energy in the beans and bring the temperature down at that required speed. So, the bigger issue is still cooling in time. 40 roast July August

3 volumes of air) as the key component in this cooling setup, and in Many of these roaster models are capable of cooling the coffee amounts of coffee in certain areas while many ways, it is. As much air as possible has to be moved through a to room temperature in less than 4 minutes, but one of the also creating areas where the bed is much cooling tray full of coffee freshly released from the roasting drum at most commonly cited issues, if cooling times are not below the shallower where more air will move more than 400 degrees F. There are a number of roaster models which 4-minute mark, is whether or not the roaster has a cooling- through faster. Air always wants to take use a single blower for both the roasting drum and the cooling tray, specific blower. the path of least resistance. and include a damper for switching the function between the two. Beyond the blower, though, there could be a number Mark Loring Ludwig of Loring Smart of other impacts on cooling times, such as ambient air Roast says his company designs its temperature. The ambient temperature in a non-climate- cooling trays to cool coffee faster by using controlled warehouse may vary by as much as 30 degrees a relatively smaller-diameter cooling Truly the biggest impact between summer and winter. The pivot arm stirring the roasted coffee in the cooling bin can also be considered. If this arm is spinning too fast, it could actually slow down cooling times. tray with a strong blower. He says, In the smaller tray the air velocity is much higher for better wind chill factor. It on cooling performance is maintenance, and the health and condition of the airflow systems. Diedrich sometimes recommends stopping the stirring arms after the coffee has been evenly distributed, about a minute, in order to pull more air more quickly through more coffee. In Staub s 2002 SCAA lecture, he talks about using a frequency drive on the stirring arm and adjusting the speed of the armature throughout the cooling process for optimal results, starting faster and slowing down as the coffee cools. The most important consideration in this regard is the even distribution of the batch. This is one of the reasons a more rapidly spinning arm slows down cooling; it collects greater travels through a deeper bed of beans, so there s more exposure, and there are no open screen areas behind the sweeps on the stirring arms where the air can take a shortcut. It works very well; cooling times can actually be under 3 minutes. (He cites a 450-degree-F start point on a 65-degree-F day in low humidity.) continued on page 44 Blower unit for a Diedrich IR12 after regular cleaning and maintenance. 42 roast July August

4 Truly the biggest impact on cooling performance is maintenance, and the health and condition of the airflow systems. Diedrich stresses the idea that the entirety of the roaster is all one system, and regular maintenance throughout that system is the key to proper cooling times. At each step of the cooling process there is the opportunity for particulate buildup from the smoke, steam and broken bits of coffee. Loring mentions that his cooling tray design also played into his desire for ease of maintenance. The smaller diameter and design adjustments to the paddle assembly allow the screen of the cooling tray to be easily lifted out for direct access and quick cleaning. Daily, weekly and monthly maintenance on a cooling system is vital for performance. The perforated bottom of the tray can easily become blocked as those perforations fill with bits of coffee or oil. Scrubbing and wiping down the tray regularly will go a long way to maintaining cooling performance, and cleaning under the tray each time it s brushed, scrubbed or wiped down is important to make sure any particulate freed during the process doesn t travel further down along the system. Removing any residual oil should be part of safety procedures, as well as quality control to prevent oil from turning rancid and contaminating other batches. Cleaning the impeller on the blower and every point in the exhaust is key. Diedrich says it s important to clean the exhaust up to the roof regularly and to check that the exhaust cap isn t too restrictive, which could lead to greater buildup. Water Quenching In many specialty roasting circles, water quenching, the other common cooling method, is looked down upon and generally completely disregarded. Its dismissal has become one of those specialty coffee tales that gets passed on from roaster to roaster without any exposure to, or understanding of, the actual practice. One of the reasons for this dismissal of water quenching is the misconception that it adds moisture back into the coffee. While some roasters may have, or currently do, use quenching to add weight back to the roasted coffee, properly water quenching coffee for cooling purposes may not involve any absorption. One roaster who uses water quenching in cooling (and who chooses to remain anonymous for proprietary reasons) says he noticed when using a quench with darker roasts where the coffee did absorb some measurable moisture, the harsher flavors of the darker roast were reduced while the sweetness was more pronounced. To clarify, water quenching is really just a step in the cooling process, and a water-quenched coffee generally finishes its cooling cycle in a cooling tray. The purpose of the quench, usually in the roasting chamber or just at the door at the drop, is simply to halt the increase in internal temperature. It takes further cooling with air to actually bring coffee down to the prescribed (room) temperature. In water quenching, the coffee is not soaking to bring the temperature down. Most commonly, the water is sprayed toward the charge as a mist for 30 to 90 seconds. This generally evaporates immediately, given the high temperature of the beans and the environment. Water quenching is much more of an issue with larger roasters and darker roasts, yet Diedrich recommends it in any machine with more than a 25-kilo capacity. Another roaster I spoke to who declined to give his name for proprietary reasons says he began experimenting with water quenching in order to control his darker roasts at the final stage. Following success with the darker roasts, he started looking at his others and was impressed with the cup results at all roast levels after using water quenching to lower cooling times across the board. Quenching is carefully monitored and compared to nonquenched batches to ensure there is no moisture being absorbed in the process. This roaster found all of his roasts sweeter while water Water quenching is really just a step in the cooling process, and a water-quenched coffee generally finishes its cooling cycle in a cooling tray. quenching helped to shorten cooling times. He also noted there was no noticeable impact on the shelf life of the coffee another of the oftcited concerns with quenching. Another question that has come up in trials and in a 2007 study by the Institute of Food Science and Nutrition at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland (titled, Influence continued on page roast July August

5 of Water Quench Cooling on Degassing and Aroma Stability of Roasted Coffee), is the impact of water quenching on degassing and shelf life. While quenching seems to perhaps lead to quicker degassing, it may not be directly linked to shelf life of roasted beans. Even so, the roaster who spoke to me about water quenching lessening the harshness of darker-roasted coffee said his research had shown that degassing was longer with water-quenched coffees. He says, Higher moisture slows degassing times as water inhibits the flow gasses in coffee beans. If quenching results in higher moisture in coffee, then it does indeed shorten shelf life. Water is a medium for reactions, and if there is more water in coffee then it will encourage those reactions. That said, proper and timely cooling does have a noticeable impact on shelf life, as longer cooling times lead to more rapid oil expression, which then leads to quicker degradation. There are a number of other factors at play here, including the moisture content of the green coffee to begin with, as well as the actual roast profile. Diedrich says another positive impact of water quenching is that air-quality restrictions become more stringent. Water quenching can help reduce the workload of the thermal oxidizer (afterburner), along with gas consumption. Remembering that the air and any smoke from the cooling tray also has to go through the exhaust and afterburner, in some cases, a water quench system can help reduce smoke present in the cooling tray. Cool Out Like almost everything in coffee roasting, the true quality impact of cooling is ripe for further research. Though the 4-minute magic number seems to be consistent with all of the roasters I spoke with for this article, there are other matters to regard. Everything from the age and density of the green coffee to differences in roast profiles could have a dramatic impact on whether or not that cooling time is truly ideal. That said, experientially, a quicker cooling time results in a sweeter cup. We ve been unfairly dismissive of water quenching, and it warrants further consideration. It could be cooler than we thought. CHRISTOPHER SCHOOLEY thinks he is a cool dude. He works for Coffee Shrub/Sweet Maria s developing resources and online content and offers roaster support. He also works for the SCAA as the coffee design and experience coordinator, and is working to open Troubadour Malting and Malt Roasting in Fort Collins, Colorado. He can be reached at ceschooley@gmail.com. 46 roast July August