Butyric Acid, also known under the systemic name “butanoic acid,” is a carboxylic acid with the structural formal CH3CH2CH2COOH. It is an important flavor compound in a number of foods in addition to beer. However, at concentrations above its beer flavor threshold (2 mg/L), it causes cheesy, rancid, baby vomit, or putrid off-flavors. Abnormal concentrations in beer can arise from infections by anaerobic spore-forming bacteria of the genus Clostridium.
Investigations into the sources of butyric acid and the bacteria involved have shown that glucose and cane sugar syrups being used as kettle adjuncts can be involved. The vulnerable areas during syrup manufacture have been found to be the handling of the starch slurry during glucose syrup manufacture and the sweet water system in cane sugar syrup manufacture. Wort production has also been identified as a potential source of butyric acid both before and after kettle boiling.
Food plant hygiene is essential in preventing outbreaks of bacteria in syrup and brewing plants, particularly during periods of high ambient temperatures and following plant shutdowns. Quality control based on the analysis of butyric acid in adjuncts, wort, and beer and the microbiological detection of anaerobic spore-forming bacteria can prevent butyric acid off-flavors in beer.