Isovaleric acid

A short, branched-chain fatty acid. Cheddar and Swiss cheeses contain it as a volatile aroma compound; whisky, wines, and beer also carry it, and it appears as an off-odour compound in natto. It is synonymous with 3-methylbutanoic acid, it adds cheesy complexity at low levels but turns sweaty and unpleasant in excess — making its control a matter of flavour balance. Ripening cultures generate it from leucine, so cheesemakers manage its formation through culture selection. Its sweaty note is a recognized defect in wines at high levels.