Isolation, Identification, and Characterization of Local Wild Yeasts for Use In Fermentation

Abstract

Inspired by spontaneously fermented beers, such as Belgian Lambic beers, American breweries have moved beyond using exclusively domesticated strains of the beer‐making yeast, Saccharomyces cerevisiae, to experimenting with a variety of different yeast species to produce unique flavors and aromas. The so‐called “funky,” “wild,” and “sour,” beers are produced using uncommon microorganisms either during or after the primary ferment. The goal of our research is to isolate, identify, and characterize wild yeasts from the local environment and to make them available to both commercial and craft brewers for making novel beers. The use of locally‐sourced yeasts could also be used by commercial brewers as a marketing angle, as is often done with local hops, grains, or water. As a source of wild yeasts, we obtained various wild and cultivated fruits growing in rural Maryland and a sample of Belgium‐style ale being aged in used oak wine barrels at Evolution Craft Brewing Company (Salisbury, MD). Yeast colonies were isolated using yeast extract/peptone/dextrose (YPD) agar plates containing antibiotics and identified by colony morphology as well as PCR amplification and sequencing of the 5.8S rRNA genes. The identified yeasts belong to Saccharomyces, Pichia, Candida, Fusarium, Torulaspora, and, most interestingly, Brettanomyces genera. The Brettanomyces yeast, which was isolated from the wine barrel ale, is normally considered a wine spoilage yeast but increasingly is being employed to create “funky” and sour flavors in beer. The growth and fermentation abilities of eight different yeast isolates were analyzed for growth in different liquid medias (YPD, hopped barley‐malt extract, and merlot grape juice) using 96‐well plates and spectroscopy. Growth rates were calculated using a modified grofit package in RStudio. Ethanol production will be determined using a colorimetric assay. Thus far, the most compelling discovery is a wild strain of Saccharomyces cerevisiae that grows comparable to a commercially‐available brewing yeast and produces pleasant, fruity aromas when fermenting barley malt extract. The complete characterization of these wild yeasts will be reported in order to identify novel wild yeasts that can be domesticated for local craft brewers.Support or Funding InformationSpecial acknowledgments to the Salisbury University Department of Biological Sciences, the Henson Undergraduate Research Award, Evolution Craft Brewery, and the National Science Foundation for funding and equipment, as well as Dr. Philip D. Anderson, Rachel Keuls, and Brittney Lozzi for their support.