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.
Volatile compounds in beer are determined through extraction with dichloromethane. These compounds serve as indicators for technological parameters, such as wort boiling, yeast pitching, aeration and fermentation as well as for the physiological condition of the yeast.
The method is suitable for beer brewed to any original gravity or to any alcohol content.
Volatile compounds in beer are concentrated through distillation and extracted with dichloromethane. The solvent phase is analyzed with a gas chromatograph. The linearity of the detector and the determination of the concentrations of analytes in the sample are achieved by using multiple concentration levels within the relevant range and through evaluation of the relative area under the peaks.