Yeast
Yeast (/jiːst/) are unicellular fungi of great importance in winemaking, responsible for the alcoholic fermentation that transforms grape must into wine. The term derives from Old English gist and Proto-Germanic roots meaning "foam" or "boil", reflecting the frothing effect of fermentation. The most significant species in oenology is Saccharomyces cerevisiae, though other genera also contribute to fermentation under certain conditions.[1]
Background
The role of yeast in wine was long unknown; fermentations were thought to occur spontaneously without a living agent. The scientific identification of yeast as the driver of fermentation was established in the 19th century, with Saccharomyces cerevisiae recognised as the principal fermentative organism in wine production.[2] Traditionally, fermentations relied on naturally occurring yeasts present on grape skins and in the cellar environment. Today, both spontaneous and inoculated fermentations are employed, depending on stylistic aims.
Characteristics
Yeasts are single-celled microorganisms that reproduce mainly by budding. In the context of wine, their defining trait is the conversion of sugars into ethanol and carbon dioxide, with numerous secondary metabolites that shape aroma and flavour.[3] While Saccharomyces cerevisiae dominates alcoholic fermentation due to its alcohol tolerance and efficiency, other species such as Brettanomyces and non-Saccharomyces yeasts may play secondary roles. These can add complexity but also risk spoilage if uncontrolled.
Use in winemaking
Winemakers may choose between spontaneous fermentations, relying on wild yeast populations, and inoculation with cultured strains for predictability and control. Commercial strains of Saccharomyces cerevisiae are selected for attributes such as fermentation vigour, temperature tolerance, and flavour enhancement.[4] Non-Saccharomyces yeasts are sometimes encouraged in early stages of fermentation to contribute aromatic diversity before Saccharomyces takes over.
Modern biotechnology has enabled the tailoring of yeast strains for specific outcomes, including enhanced aroma production, reduced volatile acidity, or adaptation to climate-related shifts in grape composition.[5] Yeast health and nutrient availability remain critical factors in avoiding sluggish or stuck fermentations.
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.
- ↑ Fleet (ed.), Wine Microbiology and Biotechnology, Harwood Academic Publishers, 1993, ISBN 978-3718653983.
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020, ISBN 978-0128161180.
- ↑ Boulton, Singleton, Bisson & Kunkee, Principles and Practices of Winemaking, Springer, 1999, ISBN 978-0834217011.
- ↑ Pretorius, “Tailoring wine yeast for the new millennium: Novel approaches to the ancient art of winemaking”, Yeast, Vol. 16, No. 8, 2000, pp. 675–729.