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Genotypic diversity of Saccharomyces cerevisiae spoilers in a community of craft microbreweries - YEAST-SPECIAL
M. Latorre, M. Hutzler, M. Michel, M. Zarnkow, F. Jacob and D. Libkind

In brewing, the yeast chosen to conduct the fermentation is one of the key factors that influences the flavor profile. Yeasts that are deliberately not under the control of the brewer are referred to as wild yeasts. The growth of wild yeasts at any stage of beer production process can cause defects that negatively impact beer quality. Wild yeasts belonging to the Saccharomyces genus present the greatest risk, given their physiological and morphological similarity to the inoculated yeast. The production of craft beer in Andean Patagonia of Argentina has grown considerably and a large community of microbreweries co-exist. Most of these have strong interactions and share many raw material suppliers. They have not yet installed proper microbial quality control strategies and wild yeast contamination is challenging. The aim of this article was to genetically characterize for the first time a high number of S. cerevisiae wild yeasts isolated from craft beer that originated from Andean Patagonia, and to study the incidence of S. cerevisiae var. diastaticus contamination. The genetic distinctiveness of 32 wild Saccharomyces was determined using multiple real-time PCR systems and PCR-amplicon capillary electrophoresis of IGS2 region. All isolates were positive for Saccharomyces cerevisiae, and 66 % were var. diastaticus (STA1 positive). Intriguingly, a single STA1 positive isolate was also positive for Saccharomyces bayanus/pastorianus/uvarum and deserves further investigation. Strain level typification showed a large diversity even in isolates from the same brewery and also permitted the detection of well-established strains within single breweries. It also evidenced possible cross contaminations among breweries. This study provides the first insight into the genetic diversity and distribution of a large set of S. cerevisiae var. diastaticus in a community of microbreweries and provides important information on how to tackle this problem in the most efficient way and thereby help improve the quality of craft beer.

Descriptors: craft beer, Patagonia, spoiler yeast, Saccharomyces cerevisiae var. diastaticus

BrewingScience, 73 (March/April 2020), pp. 51-57