WHISKY PRODUCTION

WHISKY PRODUCTION

WHISKY PRODUCTION

  • Whiskies are prepared from malted barley, exclusively in the case of Scottish and Irish malt whiskies, or with various proportions of added cereal starch for other whiskies, such as bourbon, grain and rye whiskey.
  • Blended Irish and Scottish whiskies contain a mixture of grain and malt whiskies.
  • The malt, and other cereals where used, are extracted and saccharified to form a wort, essentially as for beer brewing, except that no hops are added.
  • However, the wort is often not boiled prior to fermentation, thus retaining the activity of mash enzymes.
  • In some cases, the whole mash is fermented rather than separating the spent grains from the wort and is termed ‘in grains’ fermentation.
  • Certain fermentations, referred to as ‘sour mash’, also have a preliminary fermentation with lactic acid bacteria, usually Lactobacillus delbrueckii.
  • They are allowed to act for 4–6 h to produce 1.5% (w/v) lactic acid before being killed by boiling.
  • The yeast fermentation is then performed by specific distilling strains of S. cerevisiae, which are sometimes supplemented with surplus beer brewing yeast.
  • Some whisky yeasts are able to ferment maltodextrins because they are hybrids between S. cerevisiae and S. cerevisiae var.
  • Diastaticus which possess amyloglucosidase (glucoamylase) activity.
  • The fermentation is pitched to give an initial yeast concentration of 2×10-7cells/ml that increases to 2×10-8 cells/ml by the end of the fermentation.
  • Fermentations last for about 30–40 h and the emphasis is on ethanol yield.
  • The resultant beer is then distilled, often without separating the yeast.
  • Distillation residues may be used as an animal feed supplement.
  • Scottish malt whisky and Irish whiskey are distilled in pot stills, twice and three times, respectively.
  • Others such as Scottish grain, bourbon and rye whiskies are distilled in a continuous still, usually a Coffey-type still Products from pot stills are about 110° proof (62.9%, v/v ethanol), whereas those from a Coffeym still are at 160° proof (91.4%, v/v ethanol) and are usually diluted to around 110° proof prior to maturation (note: 100° proof is the minimum concentration of ethanol in water that still allows ignition when mixed with a standard recipe of gunpowder; pure ethanol is 175° proof).
  • The distillate is always colourless; any colour in the final product is derived from the wooden barrels in which it is matured or from added caramel colouring.
  • Maturation is usually performed in oak casks for several years, the minimum period depending upon the specific local legislation.
  • Casks can be made of new wood, often internally charred to make the wood more ‘reactive’.
  • Used casks, which have previously held sherry or bourbon, can also be used to impart particular characteristics to the whisky.
  • Wood components, referred to as ‘wood congeners’, are extracted into the whisky during maturation, giving colour and flavour.
  • These compounds include aromatic aldehydes, lactones, furfurals and tannins.
  • At the end of maturation the whisky may be blended and finally diluted, usually to 70° proof (40%, v/v ethanol) before bottling.

WHISKY PRODUCTION

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