Matthew McCarroll (1), Kelly Bender (1), Marika Josephson (2), Katherin Strain (1), Lucas A. Rose (1); (1) Southern Illinois University, Carbondale, IL, U.S.A.; (2) Scratch Brewing Company, Ava, IL, U.S.A.

Yeast, Fermentation, and Microbiology

Recently there has been a reemergence of the use of local wild yeast and bacteria in beer fermentations. While some groups have begun to examine the identity and evolution of micro-flora in the fermentation of traditional sour lambic and American coolship ale styles of beer, less work has been done to examine the use of mixed wild cultures in beers that are not traditional, slow-fermented sour beers. Following a working observation that wort formulation and brewing conditions affect the expression of yeast and bacterial characteristics in the finished beer, we set out to systematically determine the effect of IBU level on the evolution of micro-flora during primary fermentation. Mixed yeast and bacteria cultures were obtained from three breweries in three distinct regions of the United States. Beer for this study was produced on a pilot system at the Fermentation Science Institute using standard brewing methods and materials. Each of the three mixed cultures was used to ferment a replicate of the same wort at three different IBU values (0, 10 and 25) under identical conditions, in addition to a control beer using a pure yeast strain. The finished beers were then evaluated by instrumental and organoleptic analysis to identify differences in yeast expression, especially with regard to ester formation and sour character. Samples of the cultures were collected prior to and after completion of primary fermentation for each of the three brewery cultures and were submitted to genetic analysis. Results of the genetic analysis will be used to examine and quantify the micro-flora population variations through fermentation and will be examined for correlation with IBU level and identified expressions of yeast character in the finished beers.

Matthew E. McCarroll received his B.A. and B.S. degrees in chemistry and interdisciplinary studies from Appalachian State University in 1994. He then pursued graduate studies at the University of Idaho, where he received his Ph.D. degree in 1998. He then spent two years as a postdoctoral associate at Louisiana State University. In 2000 he joined the faculty at Southern Illinois University as an assistant professor and was promoted through the ranks to professor. Since 2013 Matthew has served as director of the Fermentation Science Institute at Southern Illinois University.