Glucose
Glucose is one of the two principal fermentable sugars found in grape must, the other being fructose. From a wine perspective, glucose plays a central role in alcoholic fermentation, serving as a primary substrate for yeast metabolism and directly influencing alcohol formation, fermentation kinetics and final wine balance.[1]
Occurrence in grapes
In ripe grapes, glucose and fructose are present in roughly equal proportions, though glucose typically accumulates first during berry development. Both sugars are synthesised through photosynthesis and transported to the berry during ripening, contributing to overall sugar accumulation (grape).[2]
Glucose concentration increases rapidly after veraison and, together with fructose, determines the potential alcohol of the resulting wine. Climatic conditions, yield, canopy management and vine water status all influence final glucose levels at harvest.[3]
Role in fermentation
During alcoholic fermentation, yeast preferentially metabolises glucose before fructose. This preference affects fermentation dynamics, particularly in high-sugar musts, where residual fructose may remain if fermentation becomes sluggish or stuck.[4]
The conversion of glucose to ethanol and carbon dioxide follows well-established biochemical pathways, with glucose uptake rates influencing heat production, fermentation speed and yeast health.[5]
Analytical and technological significance
Glucose concentration is routinely measured in must and wine analysis, either individually or as part of total reducing sugars. Its ratio to fructose can provide insight into grape maturity, fermentation progress and the risk of refermentation in bottled wines.[6]
From a technological standpoint, glucose availability affects yeast strain selection, fermentation temperature management and decisions regarding enrichment or arrest of fermentation.[7]
Glucose in finished wine
In dry wines, glucose is typically fully consumed during fermentation. In sweet wines, including some botrytised wine styles and fortified wines, residual glucose contributes to sweetness, viscosity and microbial stability considerations.[8]
Residual glucose, especially when present alongside fructose, may increase the risk of microbial spoilage if wines are inadequately stabilised.[9]
Regulatory context
International wine regulations define and monitor sugar content, including glucose, as part of standards governing must composition, fermentation and labelling. These frameworks aim to ensure analytical consistency and consumer transparency across wine-producing regions.[10]
See also
References
- ↑ Jancis Robinson, Oxford Companion to Wine, Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.
- ↑ PhD Jackson, Ronald S., Wine Science: Principles and Applications, Academic Press Inc, 14 April 2020. ISBN 9780128161180.
- ↑ Markus Keller, The Science of Grapevines: Anatomy and Physiology, Academic Press Inc, 19 Jan. 2015. ISBN 9780124199873.
- ↑ Pascal Ribéreau-Gayon, Yves Glories, Alain Maujean, Denis Dubourdieu, & 1 more, Handbook of Enology, Volume 2: The Chemistry of Wine - Stabilization and Treatments, Wiley, 31 Mar. 2006. ISBN 9780470010372.
- ↑ Roger B. Boulton, Vernon L. Singleton, Linda F. Bisson, Ralph E. Kunkee, & 1 more, Principles and Practices of Winemaking, Springer, 31 Oct. 1998. ISBN 9780834212701.
- ↑ Amerine & Ough, Methods for Analysis of Musts and Wines, Wiley, 1980, ISBN 9780471036732.
- ↑ Peynaud, Knowing and Making Wine, Wiley, 1984, ISBN 9780471881491.
- ↑ Andrew L. Waterhouse, Understanding Wine Chemistry, Wiley, 19 Aug. 2016. ISBN 9781118627808.
- ↑ Lawless, Wine Faults, Mitchell Beazley, 2013, ISBN 9781845337233.
- ↑ OIV, “Sugars in grape must and wine”.