All terms
Distillery glossary
Sour Mash
Sour mash is a process that uses a portion of spent mash (backset or setback) from a previous distillation to acidify a new mash, ensuring consistent pH and protecting fermentation from contamination.
Adding backset lowers the mash pH to a range yeast favors and bacteria do not, giving batch-to-batch consistency. Nearly all Kentucky bourbon is made by the sour mash process. The opposite approach, sweet mash, uses only fresh ingredients and is harder to keep consistent. Recording the backset percentage per cook supports both quality control and traceability.
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