MBAA TQ http://dx.doi.org/10.1094/TQ-50-1-0319-01 | 
VIEW ARTICLE
Acacia Baldner Cooper (1), Steven Petrovic (2), and Larry Chase (3). 1. Anderson Valley Brewing Company, 17700 Hwy 253, Boonville, CA 95415. 2. Southern Oregon University, Siskiyou Blvd., Ashland, OR 97520. 3. Standing Stone Brewing Company, 101 Oak St., Ashland, OR 97520.
Abstract
Beer flavor arises from many sources and each step in the brewing process specifically influences the flavor development of a particular beer. Simultaneously, during fermentation, desired and undesired flavors are produced. Some undesirable compounds, or “green-beer flavors,” are removed via yeast metabolism during beer maturation. The maturation method analyzed here was conducted by lowering and holding the fermenter temperature at 50 ° F (10 ° C) for 5 days, after identical specific gravities were measured sequentially for 2 days. The objective of this research was to measure the concentration changes in these green-beer flavors over the maturation period to determine if a shorter maturation would sufficiently mature the beer. Shorter maturation periods could allow the brewer a faster turnover rate of mature beers. The green-beer flavor compounds were obtained via liquid-liquid extraction and identified using GC-MS. Isopentanol (banana), phenylethanol (rose), and ethyl acetate (solvent, fruity) flavor compounds predominated. Compound concentrations decreased to 59.2, 57.7, and 58.2% of initial concentrations by day 3 of maturation, respectively, obtaining minimum concentrations of 21.21, 62.11, and 12.61 ppm. These concentrations increased by 59.5, 58.9, and 57.6%, respectively, from day 3 to day 5, nearly equaling the original concentrations at day 0. Triangle taste tests were performed on each sample to ascertain the human ability to detect off-flavor presence. Tasters with greater beer familiarity scored higher on the tests than did tasters with less experience.
Keywords: GC-MS, green-beer flavors, liquid-liquid extraction, maturation
Synthesis
The flavor and aroma of beer arises from different sources and each step of the brewing process has a specific influence on the development of these characteristics in a particular beer. During fermentation, both desired and unwanted flavors and aromas are formed. Some unwanted compounds, "green beer" flavors, are removed by yeast metabolism during maturation. In the type of maturation analyzed in this article, the temperature of the fermenter was lowered to 50ºF (10ºC) (after keeping the Ea constant for two days) and it was kept at that temperature for five days. The objective of this study was to determine if this maturation time could be long enough to consider the beer as fully matured; To this end, the change in the concentration of the "green" flavors was measured throughout the five days. The reduction in maturation time would allow the tanks to be used more efficiently. The compounds causing the "green beer" flavor were obtained by means of a liquid-liquid extraction and identified by GC-MS. Isopentanol (banana / banana), phenylethanol (pink) and ethyl acetate (solvent, fruit) were the predominant components. The concentrations of these compounds fell on the third day to 59.2, 57.7 and 58.2%, respectively, of their initial concentration, obtaining minimum concentrations of 21.21, 62.11 and 12.61 ppm. These concentrations increased from day 3 to day 5 by 59.5, 58.9 and 57.6%, practically reaching their initial concentration on day 0. Triangular tests were performed on each sample to determine the human ability to detect the presence of these off-flavors. The more experienced tasters were more successful than the less experienced tasters. Statistically significant differences were noted between green beer and beer matured by this method in almost all samples taken during the five-day maturation period.
Keywords: liquid-liquid extraction, GC-MS, maturation, "green beer" flavor
