Brewing yeasts: An overview

Yeasts are a diverse and disparate group of unicellular fungi. Amongst these, the yeast species Saccharomyces cerevisiae has arguably had the greatest impact on humankind. The species naturally possesses a number of traits that are indispensable for brewing. These include strong fermentative capacity, stress tolerance and production of volatile aroma compounds. Within the species, a number of genetically distinct groups exist, each adapted to a particular type of fermentation (bread, wine, beer, etc.). Brewing yeasts typically possess a number of additional traits, including the ability to use wort sugars efficiently, absence of off-flavour production and timely flocculation. This group can be further subdivided into the ale and lager brewing yeasts, which specialise in warm and cold-temperature fermentations, respectively. In the latter case, the low-temperature tolerance is enabled by the unique genetic makeup of the yeast (an interspecies hybrid of S. cerevisiae and S. eubayanus). Current challenges in the brewing industry, including a need for greater product diversity, are encouraging experimentation with new brewing yeasts and are inspiring a rethink of what exactly is a ‘brewing yeast’.