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

Production of Scotch and Irish whiskies: their history and evolution 147included in mash bills for manufacturing Irishwhiskey. It was contended that these grains, withtheir large husks, improved the texture of thegrain bed in the mash tun (to assist in strainingoff the clear wort from the mash solids) and thatoats influenced the flavor of Irish whiskey.Whether either or both of these effects wereimportant will probably never be known, for oatsare no longer used in the production of Irishwhiskey (Court and Bowers, 1970).Mashing and cookingMash production in Scotch and Irish distilleriesinvolves a process not unlike that used inbreweries to prepare wort for beer manufacture.However, where cereals other than malted barleyare used, the malt mashing is preceded by a hightemperature cooking process.MashingRegardless of whether the mash bill containscereals other than malted barley, the mainbiochemical changes that take place duringmashing are hydrolysis of starch, protein andother biopolymers in the meal to produce watersoluble low molecular weight compounds thatform a fermentable substrate (or wort). The majorstarch-liquefying and saccharifying enzymes are"- and ß-amylases, while the limit dextrins formedby action of amylases on amylopectin are furtherhydrolyzed by limit dextrinases.Barley malt used in the manufacture of Scotchmalt whisky is coarsely ground in a roller milladjusted to give a grind no finer than the maltwarrants. Too fine a grind can give rise to a ‘setmash’ that settles on the bottom of the mashtun to block and impede drainage of the liquid(Simpson, 1968). The mash tun is usuallypreheated with water and the perforated bottomplates are flooded before mashing commences.The meal from overhead bins is mixed with hotwater at 60-65 o C in the proportion of one partmeal to four parts water, and the mash ishomogenized by action of revolving rakes. Inthe traditional mashing process, the mash isusually loaded into the tun to a depth of aboutone meter and allowed to stand for about onehour, after which the wort is drained off fromunder the grain bed. This liquid extract, whichhas a specific gravity (SG) of 1.070-1.060 (Figure5) is collected in an intermediate vessel knownas an ‘underback’. After being cooled to around25 o C in a heat exchanger, the wort is pumpedinto the fermentation vessel. The bed of grainsin the tun is then re-suspended in water at 75 o Cand a second batch of wort is drawn off at aspecific gravity of around 1.030 and passed intothe underback. This process is known as the firstaftermash and is repeated twice more; exceptthat the dilute worts drawn off are not passed tothe underback, but are returned to the hot watertank to be used in the next mash. The wort inthe underback has a pH value of about 5.5, aspecific gravity of 1.045-1.065, and an aminonitrogen content of about 150-180 mg/L. Thespent grain residue or ‘draff’ is removed fromthe mash tun and sold as animal feed. Manydistilleries have now reduced this process to justthree water additions. Larger distilleries are nowinstalling semi-lauter tuns in place of thetraditional mash tuns. These have vertical knives,enabling the structure of the mash bed to bemaintained whilst speeding wort draining, andsparging rings to allow simultaneous draining andsparging. The result is a faster more efficientextraction without loss of clarity or changing thecomposition of the wort.Mash preparation in the manufacture of Irishwhiskey is very similar to that used in Scotchproduction, but there are certain differences. Useof a high percentage of raw barley in the mashbill (up to 60%) has necessitated the use of stonemills or hammer mills to achieve the requiredgrind. The unmalted barley is sprayed with waterto give a moisture content of about 14% andthen dried to around 4.5% moisture beforegrinding. The malted barley used is roller-milled.In recent years a plant has been installed inIreland which uses a wet milling process thateliminates the need for watering and drying of