Alcoholic fermentation
Alcoholic fermentation is the central biochemical process in winemaking by which grape sugars are converted into ethanol, carbon dioxide and a wide range of secondary compounds through the metabolic activity of yeast. This process transforms grape must into wine and plays a decisive role in determining alcohol level, aroma profile, texture and overall wine style.[1]
Definition and biochemical basis
Alcoholic fermentation is driven primarily by yeasts of the genus Saccharomyces, most notably Saccharomyces cerevisiae. Under anaerobic or low-oxygen conditions, these yeasts metabolise fermentable sugars, mainly glucose and fructose, producing ethanol and carbon dioxide as principal end products.[2]
In addition to alcohol, fermentation generates heat and a complex array of secondary metabolites including higher alcohols, esters, volatile acids and glycerol, all of which contribute to wine aroma, flavour and mouthfeel.
Role in winemaking
Alcoholic fermentation marks the transition from grape juice to wine. Its duration, temperature and kinetics influence extraction of colour and tannins in red wines, aromatic expression in white wines and structural balance across all styles.[3]
Fermentation may occur spontaneously using indigenous yeasts present on grape skins and in the winery environment, or be initiated with selected commercial yeast strains to achieve predictable outcomes.
Fermentation conditions
Key factors affecting alcoholic fermentation include sugar concentration, temperature, nutrient availability, oxygen exposure and yeast strain selection. Excessive temperatures can inhibit yeast activity or lead to undesirable aroma development, while low temperatures may slow or halt fermentation.[4]
Nitrogen availability is particularly critical, as insufficient yeast-assimilable nitrogen can result in sluggish or stuck fermentations.
Fermentation management
Winemakers actively manage alcoholic fermentation through temperature control, nutrient additions, oxygen management and vessel selection. In red winemaking, fermentation management is closely linked to cap management techniques that regulate extraction from skins and seeds.[5]
Monitoring sugar depletion, temperature and fermentation rate allows timely intervention to maintain wine quality and microbial stability.
Completion and outcomes
Alcoholic fermentation is considered complete when fermentable sugars are exhausted or intentionally arrested. Residual sugar levels influence final wine style, ranging from dry to sweet wines. Following fermentation, wines are typically clarified and stabilised before undergoing further processes such as malolactic fermentation or ageing.[6]
Regulation and standards
The OIV provides internationally recognised definitions and guidelines for alcoholic fermentation in winemaking, including acceptable practices and limits related to additives and processing aids.[7]
National regulations may further define permitted techniques, particularly within protected designation systems.
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.
- ↑ Jackson, Wine Science, Academic Press, 2020, ISBN 978-0128161180.
- ↑ Boulton et al., Principles and Practices of Winemaking, Springer, 1999, ISBN 978-0834217011.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 1, Wiley, 2006, ISBN 978-0470010372.
- ↑ Peynaud, Knowing and Making Wine, Wiley, 1984, ISBN 978-0471881491.
- ↑ Amerine & Ough, Methods for Analysis of Musts and Wines, Wiley, 1980, ISBN 978-0471036732.
- ↑ OIV, “Alcoholic fermentation in winemaking”.