Belle of Nelson poster for their sour mash whiskey
is a process used in the distilling
industry that uses material from an older batch of mash
to start the fermentation
of a new batch, analogous to the making of sourdough
bread with a starter. The term sour mash
can also be used as the name of the type of mash used in that process, and a Bourbon made using this process can be referred to as a sour mash Bourbon
. Sour mash does not refer to the flavor of the Bourbon
, as is sometimes thought.
In the sour mash process, the mash – a mixture of grain
and water – is conditioned with some amount of spent mash (previously fermented mash that still contains live yeast). Spent mash is also known as spent beer, distillers' spent grain, stillage, and slop or feed mash, so named because it is used as animal feed. The acid introduced by using the sour mash controls the growth of bacteria that could taint
the Bourbon and creates a proper pH
balance for the yeast
to work. An established and active strain
of live yeast is introduced into the mash that is to be fermented. By using an established and known fermented "sour", this fermentation process controls the introduction and growth of foreign bacteria and yeasts that could damage the Bourbon, and improves the consistency and quality of the liquor
, so that every bottle tastes as close to the same as possible. Read more...