by Jason Stone on February 18, 2014
You may have heard the term Sour mash being used many times when talking about making whiskey and have also probably seen it on many whiskey, and particularly bourbon bottles. But, if you’re a novice distiller who is looking into making his own homemade sour mash whiskey, you might still be trying to figure out what it is and how it works.
First of all, you need to know that Sour mash has nothing to do with it being sour. It gets its name from the process of making sourdough bread as it uses the same technique: it reuses material left over from the previous run in the process of fermenting a new batch. Secondly, to avoid confusion, remember that sour mash also goes by the names of stillage, spent mash, spent grain, backset, spent beer and some others, probably depending on the area you’re in.
Before hitting your copper pot still for distillation, you need to go through the process of fermentation. Your mixture of grains, water and yeast is what the mash consists of. Yeast is your essential micro-organism that lives in water, eats sugar from grains or starch, and produces carbon dioxide and alcohol as waste. In the sour mash process, your mash will also benefit from additional spent mash – a part of the old mash from your previous distillation (could be about 1/3 or a ¼ of it), which still contains live yeast. This spent mash is added for a number of reasons. First of all, it is used to control the growth of bacteria which could impact the whiskey’s taste and create a pH balance for the yeast by controlling acidity levels. Another reason is that using the established or known fermented active live yeast, it is easier to control flavor consistency and continuity between batches. This is a key aspect for commercial producers who want to keep their liquor just as tasty with every new batch they make, but it can also help you once you’ve found a recipe you enjoy.
Sour mash is a traditional and widespread process in bourbon making and a legal requirement for Tennessee Whiskey. Traditional sour mash bourbon is also double distilled in pot stills.
Sour mashing is also a process which can be used in brewing. Brewers use it to enhance the quick production of lactic acid, which gives beer its sourness. Some beers that use the sour mash process will be fermented together with brewing yeast but no boil, while other sour mashed beers will be boiled and then fermented with brewing yeast.
Sour mash is presently a very common process in the commercial distillation of whiskey but home distilling can also use the spent mash benefits, especially in the creation of a healthier, more efficient fermentation, together with consistency in flavor.