Sugar
Sugar in wine refers primarily to the natural glucose and fructose found in grapes, which provide the fundamental substrate for fermentation. The balance of sugar at harvest strongly influences both the potential alcohol level and the style of the finished wine.[1]
Formation in grapes
Sugars in grapes originate from photosynthesis in the vine’s leaves, where sucrose is produced and then transported to the berries. As grapes ripen, sucrose is enzymatically converted into glucose and fructose, which accumulate in the pulp.[2] The process of ripening involves a steady rise in sugar concentration, counterbalanced by a decline in organic acids, shaping the eventual flavour and balance of the wine.
Composition and variation
Glucose and fructose are the two dominant sugars in grapes, present in roughly equal proportions at maturity. However, their relative concentrations can vary with grape variety, vineyard climate, and ripening conditions.[3] Warmer climates typically encourage higher sugar accumulation, resulting in wines with greater alcohol potential, whereas cooler sites tend to produce lower-sugar musts with higher acidity.
Winemakers measure sugar concentration in the vineyard and winery using scales such as Brix, Baumé, or Oechsle, each offering an estimate of the likely alcohol content once fermentation is complete.[4]
Transformation in fermentation
During fermentation, yeast metabolises glucose and fructose into ethanol, carbon dioxide, and secondary flavour compounds. The efficiency of this process depends on temperature, yeast strain, and nutrient availability.[5] Musts with unusually high sugar levels can create osmotic stress, slowing or arresting fermentation. In such cases, specialised yeast strains or careful nutrient management may be required.
Contribution to wine style
The level of residual sugar after fermentation defines whether a wine is classified as dry, off-dry, or sweet. Even trace amounts can soften perceived acidity and alter the texture of the palate.[6]
Sweet wines often result from natural processes that concentrate sugars, such as noble rot, late harvest, or ice wine production. Alternatively, sugar can be preserved through winemaking interventions, including arresting fermentation, fortification, or the addition of unfermented grape must. Chaptalisation, the addition of sugar before fermentation, is another technique used in some cooler regions to raise potential alcohol, though it is regulated under many appellation systems.[7]
See also
References
- ↑ 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.
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.
- ↑ Zoecklein, Fugelsang, Gump & Nury, Wine Analysis and Production, Springer, 1999, ISBN 978-0834217011.
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020, ISBN 978-0128161180.
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.
- ↑ Zoecklein, Fugelsang, Gump & Nury, Wine Analysis and Production, Springer, 1999, ISBN 978-0834217011.