Diversity of yeasts and yeast fermentation systems
Yeasts have been exploited, albeit unwittingly, in spontaneous fermentations for millennia. However, it was not until the pioneering research of Pasteur (France) and Hansen (Denmark) over 100 years ago that the involvement of yeast cells in alcoholic fermentation and their use as pure cultures was realised. Traditionally, yeasts have been synonymous with food and beverage fermentations and the history of baking, brewing and winemaking is inextricably linked with the history of human civilisation. “Yeast” used for traditional fermentations is Saccharomyces cerevisiae, the most exploited microbe on this planet. However, S. cerevisiae is only one of around 1500 yeast species so far characterised – and this represents a small fraction of natural yeast biodiversity. Although S. cerevisiae (natural isolates and recombinant variants) remains the premier industrial microbe, there is a vast, and untapped, gene pool of yeasts awaiting further biotechnological exploitation. Several non-Saccharomyces yeasts have exceptional properties and are already being used in food, pharmaceutical and chemical fermentations. This presentation will review current and emerging exploitation of yeast biodiversity and will additionally seek to answer the question: S. cerevisiae may be the world’s oldest domesticated fermenting microbe, but is it the ideal yeast for industrial fermentations? In addition to exploiting wide yeast biodiversity, fermentation technologists have also exploited a diverse array of yeast fermentations systems. The theory and practice of batch, fed-batch, continuous, semi-continuous, synchronous, and immobilised fermentations with yeasts will be discussed together with a forecast of what is next on the industrial horizon for this fascinating group of organisms.