In addition to ethanol, yeast metabolic processes occurring during fermentation result in the formation of a number of intense, aromatic and volatile substances. These fermentation by-products primarily consist of alcohols and esters. Higher alcohols are formed from amino acids, which are converted to their corresponding α-keto acids by means of transamination reactions, through decarboxylation and reduction to alcohols. Esters are intracellular products of yeast metabolism. Esters are formed in enzymatically catalyzed reactions involving alcohol-acetyl-transferase from acetyl-CoA and the resultant alcohols produced during fermentation. These presence of these compounds can provide information about fermentation parameters. The quality of the wort (FAN profile, zinc concentration), pitching technology (aeration, number of yeast cells pitched per ml and yeast strain) as well as the temperatures at which fermentation is conducted greatly impact the subsequent concentration of fermentation by-products in the beer.
The method is suitable for beer brewed to any original gravity or to any alcohol content.
Higher alcohols and esters in beer are determined by gas chromatography using the headspace method, e.g., the volatile compounds are transferred from the gas space in the sample vial to the GC system for analysis. The method is suitable for beer brewed to any original gravity or to any alcohol content.