How accelerated aging can help to assess the physiological state of yeast in bottle-refermentation beers

Sensory Session
Caroline Scholtes, Université catholique de Louvain, Earth and Life Institute (ELIM), Louvain-la-Neuve,Belgium
Co-author(s): Etienne Bodart, Florence Peeters, Laurent Melotte, and Sonia Collin, Université Catholique de Louvain, Earth and Life Institute (ELIM), Louvain-la-Neuve, Belgium

ABSTRACT: The evolution of short chain fatty acids, esters, and fusel alcohols was investigated using various aging procedures. In unrefermented beers, a 5 day treatment at 40°C or 3 days at 60°C led to an evolution similar to what 1 year at 20°C would have induced. These assays also were representative of two refermented beers in which the yeast was in particularly good shape, as shown by the relative stability of its esters. Yet, for global sensorial analyses, both accelerated aging procedures were unable to mimic other defects, like Madeira and phenolic off-flavors. In refermented beers where yeast was autolyzed (decrease in fruity esters), accelerated aging strongly overestimated the C5, C6, C8, and C10 carboxylic acids, as well as beta-phenylethanol. In that case, released yeast glucosidases were suspected to hydrolyze glucosyl esters and glycosides available in the medium. When Brettanomyces strains were present in the bottle, heat also strongly promoted the levels of isovaleric, hexanoic, and octanoic acids. In these Belgian-style beers, accelerated aging could help to assess the physiological state of yeast in the bottle.

Graduating in 2007 as a bio-engineer from Catholic University of Louvain (Belgium), Caroline Scholtes completed her education in 2008 with a master’s degree in brewing science. In 2010, she started a Ph.D. program at the same university. Her research focuses on aging of Belgian special beers with regard to raw materials, brewing process, and storage conditions and correlates this to modification of organoleptic profile, especially Madeira off-flavor and volatile phenols. She is also a teaching assistant in beer chemistry at the same university.