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

Production of Scotch and Irish whiskies: their history and evolution 157aided by the disappearance of a bluish tinge whenwater is added to the distillate. The monitoringprocess takes place in a spirit safe secured witha Government Excise lock. Collection of thedistillate is terminated when the alcohol contenthas fallen to a specified value, although distillationof the feints or tails is continued until all of thealcohol has been removed from the low wines.The residue remaining in the spirit still is knownas ‘spent lees’, and like pot ale is either run towaste or evaporated to manufacture animal feed.The whisky distilled over in the middle fractionhas an alcohol content of 63-70 o GL.The manufacture of Irish whiskey involvesthree rather than two distillations (Figure 11). Thefermented beer is heated in the wash still, andthe first distillation (‘strong low wines’) is collecteduntil the distillate reaches a predeterminedspecific gravity. The distillate, then known as‘weak low wines’, is switched into a separatevessel. The weak low wines are pumped intothe low wines still and are re-distilled to producetwo fractions termed ‘strong feints’ and ‘weakfeints’. Strong feints are mixed with the stronglow wines in a spirit still. Distillates from this arecollected in the same fashion as in productionof Scotch. The whiskey collected usually is about89-92 o GL.Continuous distillationNo fundamental changes have been introducedinto the design of the patent or Coffey still overthe past century. Automation, particularly of thebeer feed, is now commonplace, as is continuousmonitoring of other stages in the distillationprocess. Nevertheless, many Scotch and Irishproducers of grain whiskies continue to use astill which, like the original Coffey still, has justtwo columns: a beer stripper (or analyzer) and arectifier.A description of the operation of two columncontinuous stills in the manufacture of Scotchgrain whisky has come from Pyke (1965). Inorder to obtain whisky of high quality from thesestills, they must be operated such that the alcoholconcentration of the spirit at the spirit draw trayin the rectifier is not less than 94.17 o GL. Themanner in which the precise control of stilloperation can affect the composition of thewhisky is shown in Figure 12. As illustrated, ifconditions are changed in either direction on theabscissa, the concentration of congeners willalter with a possible adverse effect on finalproduct quality.Maturation and agingFreshly distilled whisky of any type is verydifferent from the spirit that is later bottled, eithersingly or blended. The transformation is broughtabout by storing the whisky in oak barrels forperiods of time that depend on traditionalpractice and legal requirements. In general,whiskies are matured for far longer than thelegally-required period of time. The raw spirit istaken by pipeline from the distillation plant to thetank house where it is diluted with water to therequired strength and then transferred intobarrels.Maturation in barrels is accompanied by a lossof liquid by evaporation, and the relative rates ofloss of water and of alcohol determine whetherthe aged whisky has a higher or lower alcoholicstrength than that at filling. In Scotland, wherethe barrels of whisky are stored in cool,unheated, but humid warehouses, the alcoholicstrength decreases (Valaer, 1940). In contrastValaer and Frazier (1936) reported that in theUS storage conditions cause an increase inalcoholic strength. Maturation in barrels is alsoaccompanied by changes in the chemicalcomposition of the whisky. These changes areattributable to extraction of wood constituentsfrom the barrel, oxidation of components presentin the original whisky as well as those extractedfrom the wood, reactions between componentsin the whisky and removal and oxidation of highlyvolatile sulfur components by the carbon charon the inner surface of the barrel.Some of the earlier investigators reported onchanges in the composition of the major classes