Genotypic diversity of Saccharomyces cerevisiae spoilers in a community of craft microbreweries

Abstract

In brewing, the yeast chosen to conduct the fermentation is one of the key factors that influences theflavor 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 impactbeer quality. Wild yeasts belonging to the Saccharomyces genus present the greatest risk, given theirphysiological and morphological similarity to the inoculated yeast. The production of craft beer in AndeanPatagonia of Argentina has grown considerably and a large community of microbreweries co-exist. Most ofthese have strong interactions and share many raw material suppliers. They have not yet installed propermicrobial quality control strategies and wild yeast contamination is challenging. The aim of this article wasto genetically characterize for the first time a high number of S. cerevisiae wild yeasts isolated from craftbeer that originated from Andean Patagonia, and to study the incidence of S. cerevisiae var. diastaticuscontamination. The genetic distinctiveness of 32 wild Saccharomyces was determined using multiple real-timePCR systems and PCR-amplicon capillary electrophoresis of IGS2 region. All isolates were positive forSaccharomyces cerevisiae, and 66 % were var. diastaticus (STA1 positive). Intriguingly, a single STA1 positiveisolate 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 thedetection of well-established strains within single breweries. It also evidenced possible cross contaminationsamong breweries. This study provides the first insight into the genetic diversity and distribution of a large setof S. cerevisiae var. diastaticus in a community of microbreweries and provides important information on howto tackle this problem in the most efficient way and thereby help improve the quality of craft beer.