SOME NOTES ON WHISKEY FLAVOUR by Dave Quinn, Master of Whiskey Science at Midleton Distillery Ultimately, it s the wonderful flavour of Single Pot Still whiskey from Midleton Distillery that makes it all worthwhile. The overall complexity of flavour, represented by such a wide array of different whiskey types and styles, is a testament to what whiskey is made from and how it is made. Of course how the whiskey is subsequently consumed (including the physical environment) will also impact on the perceived flavour and taste of the whiskey. All of the various raw materials used in whiskey making, as well as all stages involved in both whiskey production and maturation, make some contribution to its flavour. While the alcohol aspect of whiskey is its major component, ethanol in itself has little or no flavour (or odour) and is what gives whiskey its warming and heady feeling in the mouth. All of the flavour in whiskey comes from the congeners. These are naturally occurring compounds, present in very small quantities that arise naturally during the course of the whiskey making process. There are probably many thousands of flavour important congeners present in mature whiskey. While some are well understood, that is knowledge of their flavour contribution and where they develop in the process, others are more difficult to detect and scarcely understood at all. To garner more of an understanding as to how the flavours arise in Midleton Distillery whiskeys, we must look at the entire whiskey making journey under the headings of Raw Materials, Process and Maturation.
RAW MATERIALS BARLEY AND MALT WATER As you will be aware, a key aspect in the making of traditional Irish Pot Still Whiskey is the use of a combination of malted barley (malt) and un-malted barley in the mash. While the use of malt brings a range of flavours and aromas to the final spirit, the additional use of barley impacts more on the texture of the spirit giving it a creamy and luxurious mouthfeel. Water is a key ingredient in the making of all whiskey. Its mineral and ionic composition plays a very important role in the brewing and fermentation processes and by extension on the flavour profile of the final spirit. In Midleton Distillery the water has a particular mineral content due to the fact that it flows through a karst limestone area. This quality of water allows for a very efficient mashing process and also contributes to a wholesome nutrition for the yeast during fermentation. PROCESS FERMENTATION DISTILLATION Fermentation is a key part of the whiskey making process as it is here that not only is the alcohol produced but also a wide spectrum of flavour congeners. This is accomplished by the growth of billions of individual yeast cells who grow and metabolise in the rich medium (wort) produced during the brewing (mashing) process. In addition to alcohol, the yeast cells produce higher alcohols, organic acids, esters, aldehydes and many other compounds, of which many contribute to the overall flavour complexity of the final wash or beer. Distillation, which takes place in large shiny copper Pot Stills, is where the fermented wash is turned into spirit. In Midleton, the spirit is distilled three times in order to obtain the
quality and taste profile that characterises Midleton Whiskey. During the first distillation, the fermented wash, at about 10% alcohol by volume is distilled over into Low Wines. The strength of the Low Wines can range from 25 to 45% alcohol depending on what style of Pot Still the Master Distiller is currently making. The second distillation takes a charge of Low Wines and recycled Feints which is then distilled to produce Strong Feints at about 70-72% alcohol. In this distillation the Strong Feints is a centre cut with the heads and tails being returned to the Weak Feints receiver. The Strong Feints are then distilled for a third time to produce final spirit at about 80 to 85% alcohol, again depending on the style of Pot Still Whiskey being distilled. The spirit is taken as a centre cut to ensure the correct flavour balance in the final spirit. The Heads fraction (also called foreshots) is the first runnings from the still and is dominated by highly volatile congeners (for example ethyl acetate). It also contains some fusel oils and fatty acid esters left behind in the pipes from the previous distillation. This combination of flavour characteristics makes this fraction unsuitable to be included in the spirit fraction (centre cut). The distiller will decide when it is appropriate to start taking spirit which is then directed to the spirit receiver. After a slow and deliberate spirit distillation taking about 10 hours, the levels of higher alcohols (fusel oils) and the waxy fatty acid esters start to increase at which point the distiller will re-direct the spirit flow back to the weak feints receiver to take the Tails fraction. The skill and experience of the distiller ensures that the spirit fraction is perfectly balanced and has the correct level of the various congeners to give the spirit the expected flavour profile that is demanded in Midleton Distillery.
MATURATION TYPE OF WOOD TIME Clearly, the role of maturation in the development of final whiskey flavour is critically important. In essence we move from the well understood science of distillation to the art of maturation in oak wood. During maturation whiskey undergoes a very special transformation due to the interaction of the spirit and the wood. During the time spent in cask the spirit undergoes major changes in its composition and transforms from a fiery spirit into a mellow and smooth whiskey. The colour also changes, from colourless to a rich golden amber. Two different types of oak wood are typically used in whiskey maturation, American White Oak and European Oak. These two types of wood are quite different in many respects and thus will give two different whiskeys from a similar starting spirit. Firstly they are different species of oak and so have a different composition with respect to lignin, cellulose, tannins and other volatile compounds. Also American oak casks will have been seasoned by Bourbon whiskey while the European Oak casks will have been seasoned by a fortified wine, normally Sherry or Port. In addition American Oak casks will have had their insides charred during manufacture while European Oak casks will have only been toasted. During the seasons the spirit in the cask will change in temperature as we move from winter to summer and visa versa. As the spirit warms up in the summer time it expands into the pores of the wood and this allows the spirit wood interactions to take place. The spirit restricts
back out of the wood as it cools in the winter time. These cycles continue during the many years of maturation. Various interactions take place including the extraction of wood derived congeners, the hydrolysis of wood constituents during maturation, and interactions between wood and distillate components that form new aroma compounds. Examples of wood derived congeners are oak lactones which contribute coconut aromas and eugenol which gives a spicy aroma. Also a range of tannins can be extracted from the wood which contributes to the mouthfeel of the mature whiskey. In addition another significant aspect of maturation is the removal of undesirable sensory characteristics. This aspect of maturation includes the removal of sulphur containing compounds which can be absorbed by the charred surface of the cask and subsequently degraded. The quality of the wood used for maturation is very important to the quality of the final whiskey. The source of the original casks must be carefully managed and also it is equally important that exhausted casks are culled from the population when they can no longer contribute to the maturation process.