yeast Yeast is a single-cell organism that feeds on sugars and produces ⇒alcohol and carbon dioxide as a result. The OED gives the definition 'A yellowish substance produced as a froth or as a sediment during the alcoholic fermentation of malt worts and other saccharine fluids, and used in the manufacture of beer and to leaven bread'. First attestation occurs in the Saxon Leechdoms (c.1000) as 'Læt ϸonne hwon бestandan, do of ϸa gaбellan, do ϸonne niwne бist'.
Yeast is probably the least discussed of the various elements that affect the profile of whisky, yet it is essential in the creation of alcohol, and also contributes to the character of the ⇒spirit. At one time, virtually all distillers in Scotland and Ireland used a mixture of specific distillers' yeast and much cheaper brewers' yeast, with the latter often being collected by lorry from local breweries. Today, in the interests of greater bacterial control, some distillers only use distillers' yeast, while other believe that a mixture of the two types improves the flavour of the spirit. Certainly, different strains of yeast contribute a variety aromas and flavours to the whisky ultimately produced.
Arguably, North American distillers have been aware of the importance of yeast in relation to spirit character for longer than their European counter- parts, and many US distilleries pre-cultivate their own yeast strains on site. Modern yeasts tend to promote a more predictable and less volatile fermentation than was sometimes the case in former days.
According to Grant Carmichael, former Islay general manager for United Distillers & Vintners, 'When I started in the distilleries, at Glenkinchie and Linlithgow, Lowland distilleries, each distillery had its own lorry, and every week the lorry driver and a man went off round the breweries to collect liquid yeast. The bulk of the yeast we used then was liquid, actually a mixture of dried yeast and brewer's yeast. The dried yeast started fermentation quickly, and the brewer's yeast, which had been heated previously, finished the fermentation well. Nobody uses liquid yeast anymore. Brewer's yeast is still used, but it has always been compressed now.' (TWM)
yield The quantity of ⇒alcohol produced from a given amount of ⇒malted barley. Factors that affect the yield include the quality of malted barley and the prevailing ⇒fermentation and ⇒distillation regimes.
Used as a noun, with the sense of 'The action of yielding crops or other products, production; that which is produced, produce; esp. amount of produce', the OED dates first usage of yield to c.1440. 'Eek hillis yeld is Wel gretter grayn and fewer, then in feeld is'.
According to Inge Russell, 'One tonne of malted barley, fully modified and efficiently mashed, should ensure complete extraction of the available fermented sugars, resulting in an overall distillery yield approaching 425 litres of alcohol ... Mashing efficiency is vital in achieving the maximum possible spirit yield.' (W:TP&M)