sour mash

Sour mash is a method used in whiskey production where a portion of previously fermented mash—known as "spent mash"—is added to new mash. This process helps to control the fermentation, maintain consistent flavor, and stabilize the production. The sour mash has a slightly acidic quality due to residual fermentation byproducts, which encourages the right yeast activity and inhibits unwanted bacteria. It's similar to using a starter culture in baking or brewing, ensuring quality and consistency in the final product. This technique is common in producing bourbons and other American whiskeys.