MODULE: DISTILLING UNIT: 11: PRODUCTION OF SPIRITS ...

Unit 11: Production of spirits11.2.3 Fermentation.Most distilleries maintain their own yeast strain, unlike Scottishdistilleries who buy their yeasts from a very limited number ofsuppliers. A recent development in the USA is that a few distillerieshave licensed manufactures to supply the distillery strain in driedform.KEYPOINT: Most American distilleries maintain their own yeaststrains.Yeast is propagated in a grain based medium, usually a mix of maltand rye. Most distilleries incorporate a “souring “ of the mediumeither by use of backset or by dosing with lactic acid bacteria(L.delbrueckii); this brings about a pH reduction to about 3.8. Themedium is sterilised to kill the bacteria before the yeast is added andgrowth takes place in sterile conditions. The vessel used for growth isknown as a “dona tub”. There will be several stages of propagationbefore the yeast is held in an attemperated vessel to await pitching.The logic is that as the yeast is going to ferment an acid sour mash, itshould be grown and acclimatised in similar conditions.Fermenting vessels are frequently open wooden tubs, though somedistilleries have converted to enclosed stainless steel fermenters.Fermentations are quite slow, in excess of 72 hours, and aretemperature controlled in the more modern distilleries.11.2.4 Distillation.Continuous distillation using a single column is the common processin the USA. The exception is the Labrot and Graham Distillery inKentucky which has copper pot stills arranged to give a tripledistillation. In contrast to the procedure in Scotland with pot stills thewash contains a high level of solids with both grain and yeast debris.KEYPOINT: American whiskies are almost exclusively produced bycontinuous distillation in a single column followed by a furtherdistillation in a doubler.© 2001 The International Centre for Brewing and Distilling 10