Investigation of Beer Flavor by Gas Chromatography-Olfactometry

Gas chromatography-olfactometry (GCO) is an analytical technique for evaluating the aroma characteristics of volatile constituents separated by gas chromatography (GC). This article presents three case studies employing the GCO technique in brewing, including investigation of kettle hop aroma, an off-aroma in beer, and aged-beer aroma. The kettle hop aroma was studied using a GCO technique called CharmAnalysis (DATU, Inc., Geneva, NY) and beer strongly hopped with Oregon Cascade hop pellets at 45 min before end of kettle boil. CharmAnalysis can quantitate the intensity of an aroma detected at a sniff port. It revealed that linalool was an important aroma compound in hopped beer and that phenylethyl alcohol and two coeluting, tentatively identified constituents were important aroma compounds in hopped and unhopped beers. In a second study, GCO was employed for investigating an objectionable aroma described as medicinal/phenolic/Band-Aid in a production beer. GCO was able to reveal the eluting off-odor that matched the off-aroma character in the beer. In a third case study, a quantitative GCO technique called AromaTrax (Microanalytics, Round Rock, TX) was employed to determine aged-beer aroma. This technique revealed that quantitative changes of many minor components possessing unpleasant aroma notes, particularly the carboxylic acids, were involved in aged-beer aroma.