Impact of dried, creamed and cake supply formats on the genetic variation and ethanol tolerance of three saccharomyces cerevisiae distilling strains

Abstract

Scotch whisky fermentations typically employ high-gravity fermentation practices to maximize product formation and tominimize both energy and water inputs. This approach increases ethanol concentrations at the end of fermentation, creatingstressful conditions for the yeast. In this work we examined the relative tolerance of four Saccharomyces cerevisiae distillingyeast strains, supplied in dried, creamed, cake or slurry format, to ethanol under CO2-induced naerobic conditions. The cellswere assessed for their capacity to recover and grow on inhibition spot plates and to maintain cell viability in ethanol-dosedsuspensions. Variations in ethnol tolerance were observed between strains and between the same strain supplied indifferent formats. The creamed yeast format typically exhibited a higher tolerance to ethan. One possble explanationfor this observation is that cells surviving the dehydration and rehydration pocess might incur sub-lethal genome damage. Thus the genetic integrity of the most ethanol-tolerant strain was assessed as a function of supply format (two dried and onecreamed). The mitochondrial DNA was examined using mitochondrial restriction fragment length polymorphism and thechromosomal DNA using pulsed field gel electrophoresis and polymerase chain reaction with both ITS and delta-specificprimers. In one dried yeast sample, genetic integrity was compromised, highlighting the requirement for yeast intake qualityassurance programmes. © 2012 The Institute of Brewing & Distilling.