Biomass production optimization and quality assessment of Saccharomyces eubayanus starter cultures for their application in the craft brewing industry

Abstract

The wild yeast Saccharomyces eubayanus (parental of the lager brewing hybrid yeast) has been intensively studied for brewing applications since its discovery in Patagonia (Argentina), and then in other parts of the world. In this work, cultures of this non-conventional yeast in different physiological conditions were tested in terms of viability and vitality, to understand its behavior and provide tools for biomass quality assessment for brewing. Four dyes were analyzed, and alkaline methylene violet turned out to be the most accurate for S. eubayanus viability measurements. Regarding vitality, cultures in exponential and stationary phases presented shorter lag phase and greater acidification power, indicating a better metabolic state; contrary to what was observed in cultures under starvation and refrigerated for 30 days (stressed); however, these presented the highest subsequent fermentation rate. In addition, culture medium for propagation was optimized from malt extract. Plackett–Burman design allowed identifying the most influential factors for biomass production: yeast extract and acid casein peptone, which were optimized by applying a CCD-RSM. Finally, scaling-up (20 L) allowed the obtention of S. eubayanus starter cultures with an adequate biomass quantity and quality for being transferred to the brewing industry.