the common name for hexanoic acid, a short-chain saturated fatty acid that can be created by the metabolic activity of yeasts. It is one of three fatty acids named in relation to Capra, the genus of goats; the others are caprylic and capric acids. The names are derived from the high amounts of these fatty acids found in goat’s milk, which give the milk its characteristic odor and flavor.

Caproic acid gives a normal flavor in goat’s milk, but it is usually not desirable in beer. In beer it has a pungent, sweaty, cheesy aroma. It is excreted by yeast during extended lagering at warm temperatures and high yeast cell counts. The condition of the yeast also influences fatty acid excretion and beers fermented warm under pressure show increased concentrations of these fatty acids (and corresponding esters) during lagering. Normal amounts of hexanoic acid are in the 1–2 ppm range, whereas increased amounts can have negative effects on both foam and taste. To avoid these effects, brewers often remove yeast as soon as feasible after fermentation. Where time is an issue, a centrifuge is sometimes used between fermentation and lagering tanks, although in this case the process is usually calibrated to leave some yeast behind to assist in maturation.

“Wild” Brettanomyces yeast strains tend to produce caproic acid in large amounts, and although this creates flavors unsuitable for most beer styles, some brewers may desire it as a complexing agent. Caproic acid is a major feature of lambic aromatics and beers intentionally inoculated with Brettanomyces cultures will often show distinctly “funky” characteristics.

See also brettanomyces, caprylic acid, and lambic.