lactobacillus (LAB) is a large grouping of bacteria, all of which produce lactic acid. They can be derived from the raw material used for fermentation (they are naturally present in many such materials) but in distilleries tend to be in highest concentration within pipes and fermenting vessels. Research has shown that each distillery has its own fingerprint of LAB, created by its particular operating regime; these bacteria colonies can help create an individual character in the distillery’s product. LAB’s role within flavor creation comes during fermentation. Which flavor compounds are produced depends on a number of factors, primarily the specific LAB colony within the distillery and the length of the fermentation. See fermentation.
As yeast cells die, autolysis starts and LAB start to multiply. The dead yeast cells contain high levels of fatty acids. These are changed (hydroxylated) into lactones, which produce aromatic compounds identified as soft orchard and tropical fruits. See lactones.
The acidity of the fermenting liquid also continues to rise, which in turn helps to trigger other LAB. The combination of LAB metabolization of lactates and acetates, alcohol, and higher acidity helps to produce the grouping known as esters. LAB can also reduce smoky (phenolic) aromas. See esters and phenols.
The cleanliness of a distillery also plays a part in lactobacillus generation. Fermenting vessels made of stainless steel (which can be more efficiently cleaned) will have lower LAB levels. Wooden fermenters, conversely, will contain higher levels. Distillers who use stainless steel fermenters but wish to run longer fermentations to produce specific flavors will clean but not sterilize the vessels in order to preserve the LAB colony.
Priest, Fergus G. “Lactic Acid Bacteria: The Uninvited but Generally Welcome Participants in Malt Whisky Fermentation.” Microbiology Today, February, 2004, 16–18.
By: Dave Broom