Chapter 11 Production of Scotch and Irish whiskies: their history and ...

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148 T.P. LyonsFigure 5. Flow diagram showing the mashing cycle in a Scotch malt whisky distillery.the unmalted barley. Mash tuns used in Irishwhiskey distilleries differ from those used tomake Scotch in that they are larger, simplybecause these distilleries have stills with a greatercapacity than those in Scotland. (This differencedates back to when there was a flat rate of taxper still in Ireland, rather than a tax per gallon ofproduct.) Moreover, the mashing cycle differsin that the weak wort from the first aftermash isnot passed to the underback, but is mixed withworts from the second and third aftermashes tobe used in the subsequent mash (Lyons, 1974).Cooking followed by malt mashingThe wheat, corn and rye used in production ofScotch grain whisky must be cooked beforebeing added to the mash containing malted barleyin order that the starch in these grains canbecome gelatinized and accessible to the maltenzymes. Traditionally, cooking was carried outas a batch process, but it has to some extentbeen superseded by continuous processes.For batch cooking, the grain is freed fromextraneous material by passage through screensand then ground either in a pin-type mill or ahammer mill. It is then conveyed to the cookerand subjected to a cooking cycle involving hightemperatures and pressures designed to bringabout complete gelatinization of the starch.Inadequate cooking will sometimes leave starchgranules intact in the mash, while excessiveheating can cause caramelization and thereforeloss of sugar and decreased spirit yield. Pyke(1965) has provided an account of the cookingof corn in its production of Scotch grain whiskyand a similar process is still used today. Theconventional cooker is a horizontal cylindricalvessel capable of working at pressures up to 90psi (63 x 10 4 Pa), and fitted with stirring gear. Atypical cycle in cooking corn might consist of 1-1.5 hrs of heating with live steam injection toreach a temperature of 120 o C and a pressure of15 x 10 4 Pa. The mash is held at this temperatureand pressure for a further 1.5 hrs. The liquid usedfor the mash is often that from the third aftermashmentioned earlier. At the end of the cookingtime, the pressure is released and the hot cookedcorn mash is blown directly into a saccharificationvessel containing the malted barley suspendedin hot water. Cold water is then added to bringthe temperature in the mash tun to around 63 o C.Good mixing is also essential at this stage; and
Production of Scotch and Irish whiskies: their history and evolution 149failure to achieve it can lead to the entire mashsolidifying. The need for rapid cooling of thecorn mash was emphasized by Murtagh (1970),who showed that with slow cooling or holdingat a temperature around 82 o C lipid-carbohydratecomplexes could be formed that are notfermentable and can lead to a loss of 1-2% inspirit yield.After a suitable mashing period, the mash maybe filtered as described previously. Morecommonly, the entire mash may be pumped viaa heat exchanger into a fermenter. Pyke (1965)has published the composition of a typical Scotchgrain whisky mash (Table 2).Table 2. Chemical composition of a typical scotchgrain mash*.Total soluble carbohydrate (as glucose) 9.00Insoluble solids 2.20Fructose 0.13Glucose 0.29Sucrose 0.28Maltose 4.65Maltotriose 0.96Maltotetraose 0.45Dextrin 2.54Amino nitrogen (as leucine) 0.09Ash 0.27containing P 2O 50.09K 2O 0.09M gO 0.02µg/mlThiamin 0.46Pyridoxine 0.61Biotin 0.01Inositol 236Niacin 11.1Pantothenate 0.71*Pyke, 1965.In the manufacture of Scotch grain whisky, theproportion of malted barley in the mash bill isusually around 10-15%, a proportion far greaterthan that required merely to provide a source ofamylolytic enzymes. It is a practice of long%standing, and is done to obtain the required maltflavor in the grain whisky. This was noted as earlyas 1902 by Schidrowitz and prompted furthercomment from Valaer in 1940.Continuous cooking has been adopted inrecent years in Scotland. Stark (1954) listed theadvantages of using continuous cooking. Whilepractices vary to some extent in differentdistilleries, essentially the cereal is slurried ataround 50 o C and then pumped through a steamjetheater into the cooking tubes where theresidence time is normally 5-10 minutes. Thecontinuous cooker has a narrow tube (6-16 cmin diameter) which reduces the incidence ofcharring and carbon deposition. The mash passesthrough the tube at about 20 meters/minute, withthe temperature reaching near 65 o C and thepressure 65 psi (40 x 10 4 Pa).FermentationThe objectives in fermenting a whisky distillerymash with strains of Saccharomyces cerevisiaeare to convert the mash sugars to ethanol andcarbon dioxide while producing quantitativelyminor amounts of other organic compoundswhich contribute to the organoleptic qualities ofthe final distilled product. Fermenting vessels varyconsiderably in volume, depending on thedistillery. The small Scotch whisky distillery atEdradour near Pitlochry, for example, hasfermenters with a capacity of only 4,500 liters.In contrast, other Scotch and Irish pot whiskeydistillers have fermenters with a capacity in therange 50,000 to 150,000 liters. Much largerfermenters are found in Scotch grain whiskydistilleries. Traditionally, the smaller pot distilleryfermenters were made of wood, usually of larchor Oregon pine, but in recent years they havebeen constructed of steel or aluminum. In someScottish distilleries, timber is still used as acovering material.When the fermenter is partly filled, the mashis inoculated with a suspension of Saccharomycescerevisiae. The source of yeast varies with thelocation and size of the distillery. Distilleries in
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Chapter 11 Production of Scotch and Irish whiskies: their history and ...

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