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

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144 T.P. Lyonssuitably low moisture level for storage, curing togive it the appropriate flavor and retainingsufficient enzyme activity (Simpson, 1968). Inmaltings attached to the distillery, the kilntemperature is increased slowly over a 48 hrperiod to achieve an even rate of drying and thedesired flavor. The latter character is achievedby fuelling the furnace with peat during the earlypart of the kilning period when the green malt ismoist and readily absorbs the peat smoke or‘reek’. In mechanical maltings the green malt isdried at a faster rate with a forced-air draught,but a supplementary peat-fired kiln is often usedto produce flavored malts. The amount of peatused varies with different maltings. Some of thedistilleries on Islay in Scotland specialize inproducing a whisky with a very pronounced peatflavor, and they therefore use heavily-peatedmalts. Malted barleys used in the manufactureof Scotch grain and Irish whiskies are not driedover a peat fire. They generally have a greaterenzyme activity, so the relatively small proportionof malted barley used in the mash containssufficient enzyme activity to convert all of thestarch in the mash (principally supplied byunmalted cereals) into fermentable sugars. Thegreater enzyme activity in these malted barleysis reflected in their nitrogen content. Malts usedin production of Scotch grain whisky have anitrogen content of 1.8% or higher (comparedwith a brewer’s malted barley with a nitrogencontent in the region of 1.5%) (Hough et al.,1971). Malting aids, such as gibberellic acid andbromate, are not normally used in productionof malted barley for whisky manufacture.Because of the high cost of malted cereals,considerable effort has been expended by thewhisky distiller in attempting to devise methodsthat allow prediction of the yield of alcoholexpected using different proportions of maltedbarley in the mash bill. Unfortunately, the methodscustomarily used by the brewer, such as thoserecommended in Great Britain by the Instituteof Brewing Analysis Committee (1975), haveproved of limited value. The brewer has usedmeasurements of diastatic power, expressed asthe Lintner value, which is a measure of theextent of saccharification of soluble starchpresent in a cold water extract of the malt (LloydHind, 1948) as an indicator of malt quality.Diastatic activity measured in this way includescontributions from both "- and ß-amylases.However, Preece and his colleague (Preece,1947; 1948; Preece and Shadaksharaswamy,1949 a,b,c) have shown that high ß-amylaseactivity, as determined by the Lintner value, isnot always accompanied by high "-amylaseactivity. Pyke (1965) showed that the Lintnervalue of a malt is only useful for predicting thespirit yield in manufacture of Scotch grain whiskywhen the proportion of malted barley in themashbill is low (Figure 3). Determination of "-amylase activities of the malt gave a lesssatisfactory correlation than the Lintner value, anobservation which agrees with that made earlierby Thorne et al. (1945). Further evidence for theunsuitability of employing traditional maltspecifications for predicting performance inwhisky manufacture has come from Griffin(1972).Although the degree to which a malted barleyhas been peated can to some extent be assessedby smell, such is the importance of this characterin malt that it must be determined in a morerigorous fashion. Peat smoke or ‘reek’ containsa wide range of compounds, but it is generallyheld that the peaty character is imparted to themalt largely as a result of absorption of phenols.For some years, Scotch distillers used a methodbased on a reaction of phenols with diazotizedsulphanilic acid. A lack of specificity in thismethod, coupled with the instability of thediazonium salt, prompted MacFarlane (1968) torecommend an alternative method involvingextraction of phenols from malt with diethyletherunder acid conditions with absorptiometricmeasurement of the color developed when thephenols are reacted with 4-aminophenazone.MacFarlane applied the method to a wide varietyof malts, both peated and unpeated, andreported values ranging from zero (for anunpeated grain) to as high as 9.4 ppm for a maltproduced on Islay in Scotland. (It has beencalculated that to obtain a malt with 10 ppmphenols, one tonne of peat must be used fordrying each tonne of malted barley).
Production of Scotch and Irish whiskies: their history and evolution 145Scotch whisky distillers have been concernedby the possibility that colorimetric methods, suchas those recommended by MacFarlane (1968)and Kleber and Hurns (1972), may not assay allof the organoleptically-important compounds thatmalt acquires as a result of peating. To examinethis possibility, MacFarlane et al. (1973)produced peat smoke condensate on a laboratoryscale and separated the oil and aqueousphases from the wax fraction, as only the twoformer would contain components that mightappear in the distilled whisky. Six compounds,namely furfural, 5-methylfurfural, guiacol, phenol,D-cresol and 5-xylenol, were detected in theaqueous fraction by gas liquid chromatography(GLC). The peat smoke oil was more complex,and no fewer than 30 peaks, some of themcreated by more than one compound, wereobtained by GLC. The compounds includedhydrocarbons, furfural derivatives, benzenederivatives and phenols. The authors stressed thatusing their GLC techniques, 3,5-xylenol ismasked by the peaks of m-ethylphenol and D-ethylphenol, two compounds thought to makean important contribution to peat aroma andtaste. Figure 4 shows gas liquid chromatogramsof extracts of a peated and a unpeated malt.Unmalted cerealsFewer problems are encountered in arriving atspecifications for the unmalted cereals used inwhisky manufacture, namely wheat, corn, rye andbarley. The corn (varieties of Zea mays) used inmash bills for manufacturing Scotch grainwhiskies is usually of the yellow dent type,generally obtained from France. Occasionallywhite corn is used, and it is reputed to give ahigher alcohol yield. Corn is a popular grainbecause it has a high content of starch that isreadily gelatinized and converted intofermentable sugars. The US has imposed controlson the quality of corn used for whiskymanufacture. In the US there are three gradesof corn, with only grades 1 and 2 being approvedfor spirit manufacture. In Great Britain, on theother hand, the corn used is normally grade 3on the US scale.Unmalted barley used in manufacture of Irishwhiskey has a quality intermediate to that usedfor malting and that used for cattle feed. In thisway, the maltster can select the best barleyavailable on the market at the time of purchase.For many years, a small percentage (about 5%of the total) of unmalted oats (Avena spp.) wasFigure 3. Relationship between the diastatic activity of a Scotch grain whisky mash bill and spirit yield.Laboratory fermentations were conducted using mash bills containing different proportions of malt mixed withcorn, and therefore with different Lintner values. It can be seen that only when the proportion of malt is ratelimitingcan spirit yield be correlated with the Lintner value (Pyke, 1965).
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