Wild australian yeast: to beer and beyond

Kerr ED1, Howes M2 and Schulz BL1

  1. School of Chemistry and Molecular Biosciences, The University of Queensland.
  2. Newstead Brewing Co.

Yeast is essential for making beer, as it produces ethanol and contributes heavily to its flavour and sensory properties. Commercial breweries typically use Saccharomyces cerevisiae for production of ales, and Saccharomyces pastorianus for lagers. The most notable exceptions to this are sour, lambic, and American coolship ales, where wort is exposed to a mix of environmental yeast and bacteria, rather than commercially cultivated Saccharomyces strains. Spontaneous environmental inoculation for beer fermentation is becoming more common and rather trendy. However, such wild ferments have unpredictable rates, efficiencies, and end products. We propose instead to isolate clonal strains of wild yeast, to allow efficient and predictable production of beers with interesting and diverse flavour profiles. Here, we describe a method for isolating and characterising wild yeast for brewing unique and interesting beers. Yeast is collected from the wild and grown on solid selective media to isolate clonal strains. These clones are identified by internal transcribed region (ITS) PCR and Sanger sequencing. Each clone is grown in liquid wort to measure growth on oligomaltose, and to identify fermentation end products. Gas chromatography mass spectrometry (Headspace-GCMS) is then used to quantify ethanol and other fermentation end products from fermentation. Strains that efficiently grow and produce ethanol are then fermented, and flavour profiles are measured using Headspace-GCMS. Intermediate upscaling of strains with efficient growth, ethanol production, and pleasant or interesting smelling ferments is then performed in a food grade brewery to allow sensory evaluation. This workflow provides the tools needed go from environmental yeast isolation to producing brewery-quality beer. This workflow also has uses beyond brewing, allowing quick and robust identification of wild yeasts and identification of compounds related to flavours in diverse beverages or industrial applications.