Sour Mash

Sour mash describes the use of leftovers from a previous fermentation in bourbon production to stabilize the pH in the current fermentation. The remaining liquid, called backset or stillage, is added to the new mash and lowers the pH as well as alters the yeast environment, contributing to a more predictable fermentation and more consistent batches across production.

• Purpose: Stabilize the pH in the mash environment and ensure a more uniform fermentation, reducing the risk of incomplete fermentation and delivering a more consistent flavor profile.

• Material and process: Backset consists of the liquid remaining after distillation of a batch. It contains organic acids and metabolites, which lower the pH and affect the microflora in the upcoming fermentation.

• Effect on taste and texture: Can contribute to a light sour note and a more balanced bourbon profile. Variations depend on the amount of backset and the mash recipe.

• History and context: The method spread in American bourbon production, particularly in Kentucky in the 19th century, as a way to reuse distillation residues and achieve uniformity in production.

• Notes: Not all bourbons use sour mash; practice and style vary among producers and regions.