production
Sour mash
No legal definition
The near-universal American practice of adding a portion of spent, acidic stillage (backset) to each new mash to lower pH, discourage spoilage and promote consistent fermentation.
Not a legal term
No whisky regulation in Scotland, Ireland, the United States, the EU or Japan defines this. It is a trade or marketing term, so it is only actionable if its use is actively misleading.
Worth knowing
27 CFR part 5 contains no definition of sour mash, and no US whisky type requires it. Tennessee's statute uses the phrase 'Tennessee Sour Mash Whiskey' without defining it. Trade convention is roughly a quarter of the mash volume as backset.
Related terms
Last reviewed 2026-07-30 · All glossary terms