Part 4: How is Whisky Made? Fermentation

30-12-2016 By Emily Stockden

After cooling, the wort is passed into large holding tanks called washbacks which can hold from 9 000 all the way up to 45 000 litres of liquid. They’re typically made from wood but nowadays most are made from stainless steel. This is really where fermentation starts as yeast is added at this point. Just as distillers take the selection of grain very seriously, so they take the selection of the strain of yeast used as seriously because it has a slight impact on the flavour of the final spirit.

distillery workers touching wort  in a washback


So what does yeast do? Essentially it converts the sugar in the wort to crude alcohol. Fermentation takes approximately 48 hours although some distilleries leave the fermentation process to run its course a little longer as they are aiming to get certain characteristics from the fermentation process.

The liquid at the end of this process is called wash and it will contain a low alcohol by volume (ABV) of between 5% and 10%. This is the stage when it’s most similar to beer or ale, but at this stage the whisky fork in the road requires distillation rather than brewing.

a glass of wash

A glass of wash