Alcoholic fermentation in brewing and distilling processes produces many compounds besides ethanol. Many of these compounds belong to groups such as alcohols, esters, di-methyl sulfate, and vicinal diketones, which add both pleasant and unpleasant flavors to the beverages. Although ethanol is most prevalent in concentration, many of these compounds that are in much lower concentrations are responsible for imparting many of the interesting and key flavors to the beverage. This project looked at how the concentration of these flavor active compounds changed over 9 fermentations in which the same yeast was used for each fermentation. Since it has been reported that as yeast age, their metabolism changes, it is probable that the concentrations of flavor causing alcohols also change. This means that the flavor profile of the beverage changes, which is undesirable for a brewery or distillery looking for consistency in their products. A quantitative protocol was developed that allowed for the measurement of many flavor causing compounds that are at or below the taste threshold of the average human being. Gas chromatography was used for the separation and quantitation of these compounds. Over the 9 generations, the results showed that as the generation of the yeast increase, they become more efficient at decreasing some of the flavor compounds, diacetyl and acetaldehyde, where as some increased, isoamyl alcohol, 2-methyl-1-propanol, and 2-methyl-1-butanol, while others remained constant, DMS, ethyl acetate, and 2,3-hexanedione. Future research will involve more method development for more quantitative accuracy at lower concentrations in order to more accurately measure the flavor active alcohols.

Quantitative determination of fusel alcohols, esters, di-methyl sulfide, and vicinal diketones in craft beer during a nine generation serial re-pitching experiment

2019 Spring National Meeting

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