Yeast metabolism
Yeast metabolism refers to the biochemical processes by which yeast converts substrates in grape must into ethanol, carbon dioxide and a wide range of secondary metabolites during alcoholic fermentation. In winemaking, yeast metabolism is central to fermentation kinetics, alcohol production, aroma formation and overall wine balance.[1]
Role in winemaking
During fermentation, yeasts—most commonly strains of Saccharomyces cerevisiae—metabolise sugar primarily in the form of glucose and fructose. Through glycolysis and subsequent metabolic pathways, sugars are converted into ethanol and carbon dioxide, while energy is generated to sustain yeast growth and reproduction.[2]
Beyond alcohol production, yeast metabolism is responsible for the formation of numerous compounds that shape wine aroma, flavour and texture, making yeast selection and fermentation management critical oenological decisions.
Primary metabolic pathways
The core of yeast metabolism in wine fermentation is the glycolytic pathway, followed by alcoholic fermentation under anaerobic conditions. Key stages include:
- Uptake and phosphorylation of sugars
- Conversion of hexoses to pyruvate
- Reduction of pyruvate to ethanol
These processes are influenced by temperature, oxygen availability and nutrient status of the must, particularly nitrogen content.[3]
Secondary metabolites
In addition to ethanol, yeast metabolism produces a range of secondary metabolites that contribute to wine character. These include:
Many of these compounds arise from amino acid metabolism and lipid synthesis pathways. Their concentrations and sensory impact depend on yeast strain, fermentation temperature and nutrient availability.[4]
Esters formed during yeast metabolism are particularly important contributors to fruity aromas in young wines.
Nitrogen and yeast health
Assimilable nitrogen is a key factor regulating yeast metabolism. Insufficient nitrogen can lead to sluggish or stuck fermentation, while excess nitrogen may increase the formation of undesirable by-products. Winemakers often manage nitrogen levels through vineyard practices or controlled additions in the cellar.[5]
Oxygen and metabolism
Although alcoholic fermentation is largely anaerobic, limited oxygen exposure early in fermentation supports yeast sterol and fatty acid synthesis, improving cell membrane integrity and fermentation reliability. Excess oxygen later in fermentation, however, can alter metabolic pathways and affect wine stability.[6]
Yeast selection and control
Modern winemaking increasingly relies on selected yeast strains with defined metabolic profiles. These strains may be chosen to enhance specific aroma compounds, improve fermentation robustness or reduce the risk of off-flavours. Advances in yeast research and biotechnology have expanded the range of metabolic behaviours available to winemakers.[7]
See also
References
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020, ISBN 9780128161180.
- ↑ Boulton et al., Principles and Practices of Winemaking, Springer, 1999, ISBN 9780834217011.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 1, Wiley, 2006, ISBN 9780470010372.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Waterhouse, Sacks & Jeffery, Understanding Wine Chemistry, Wiley, 2016, ISBN 9781118627808.
- ↑ Peynaud, Knowing and Making Wine, Wiley, 1984, ISBN 9780471881491.
- ↑ Pretorius, “Tailoring wine yeast”, Yeast, ISSN 0749-503X.