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 gas chromatography headspace method is used to determine compounds which serve as indicator substances for technological parameters, such as wort boiling, yeast pitching and aeration, fermentation as well as the physiological state of the yeast.
The method is suitable for beers of all original gravities and of any alcohol content.
The gas chromatography headspace method is used to determine the higher alcohols and esters present in beer, i.e., the volatile compounds are transferred from the headspace in the sample vial into the GC system for analysis. The following substances are measured in this analysis:
Acetaldehyde
Propanol-1
Ethyl acetate
2-Methylpropanol
3-Methylbutanol
2-Methylbutanol
2-Methylpropylacetate
Butyric acid ethyl ester
3-Methylbutyl acetate
2-Methylbutyl acetate
Hexanoic acid ethyl ester