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P-42. The analysis of green-beer off-flavors using liquid-liquid extraction and GC-MS

Presenter: Acacia Baldner, Standing Stone Brewing Company, Ashland, OR. Coauthor(s): Larry Chase, Standing Stone Brewing Company, Ashland, OR; Steven Petrovic, Southern Oregon University, Ashland, OR.

There are many techniques for maturing beer in cylindroconical fermenters prior to transferring the beer to serving vessels or bottling it. At Standing Stone Brewing Company a common method of maturing ale-style beers is to allow the beer to age in the fermenters at a lower temperature than the active fermentation temperature for a period of a few days. The method analyzed here is conducted by lowering the fermenter temperature to 50°F from the active fermentation temperature of 68°F and holding that temperature for 5 days after an identical specific gravity is measured 2 days in a row. This allows yeast the opportunity to metabolize unwanted flavor by-products produced during the initial fermentation period. The objective of this research is to measure the concentration changes in these green-beer off-flavors over the 5-day 50°F maturation period. Analyses of these concentration changes would allow brewers to identify whether there is a significant flavor change throughout the entire maturation period or if a shorter maturation period would also adequately improve beer flavor quality. A shorter maturation period would allow the brewer a faster turnover rate of moving beer out of fermenters into serving vessels or bottles, freeing up space for additional beers to be fermented. The beer analyzed for this research was a brown, session-style ale taken from Standing Stone Brewing Company. Liquid-liquid extraction into a 2:1 pentane/dichloromethane solution was used to isolate the green-beer volatiles from samples collected throughout the maturation period. These extracts were then concentrated using a stream of nitrogen, and the resulting concentrates were analyzed via gas chromatography–mass spectrometry (GC-MS). The predominant off-flavor compounds detected by GC-MS were identified as isopentanol (also known as isoamyl alcohol, with a banana/solvent flavor), ethyl acetate (also known as acetic ester with a fingernail polish/fruit flavor), and phenylethanol (roses, estery, spicy flavor). Triangle taste tests were performed as a sensory evaluation technique to distinguish between mature and immature beer. From the taste tests it was determined that an average of 75% of the samples were identified correctly.

Acacia Baldner studied chemistry and biology at Southern Oregon University and in 2011 earned a bachelor’s degree in biochemistry. During her time at SOU she was an avid homeb rewer, which sparked her passion for brewing and was the impetus in her decision to become a professional brewer. This passion has led Acacia to begin entering her beers in local home-brewing contests, and in September 2010, she was awarded 2nd place for her blackberry lambic at the Jackson County Harvest Fair. To achieve her dream of becoming a professional brewer, Acacia will attend the Master Brewer Program at UC Davis in January 2012.