Butyric Acid
An off flavor in beer that causes cheesy, rancid, putrid, and baby vomit-type flavors at concentrations above its beer flavor threshold.
Bacteria during mashing and sweet wort separation can cause higher butyric acid concentrations, as well as cane sugar syrup used as a kettle adjunct. Occasionally, bacterial spoilage of packaged beer can cause high butyric acid concentration.
Brewers can prevent off-flavors in beer caused by butyric acid by performing quality control, analyzing the presence of butyric acid in adjuncts, wort, and beer.