Grape composition: Difference between revisions
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'''Grape composition''' refers to the physical, chemical and biochemical constituents of the grape berry that determine the potential quality, style and stability of [[wine]]. The relative proportions of [[sugars]], [[acids]], [[phenolic compounds]], aroma precursors and nutrients formed during grape development provide the fundamental [[raw material]] upon which all subsequent [[winemaking]] processes act.<ref>Robinson | '''Grape composition''' refers to the physical, chemical and biochemical constituents of the grape berry that determine the potential quality, style and stability of [[wine]]. The relative proportions of [[sugars]], [[acids]], [[phenolic compounds]], aroma precursors and nutrients formed during grape development provide the fundamental [[raw material]] upon which all subsequent [[winemaking]] processes act.<ref>Jancis Robinson, ''Oxford Companion to Wine'', Oxford University Press, 17 Sept. 2015. ISBN 9780198705383.</ref> | ||
== Berry structure == | == Berry structure == | ||
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== Sugars == | == Sugars == | ||
Sugars in grapes are produced through [[photosynthesis]] and accumulate primarily as glucose and fructose during ripening. Sugar concentration is a key determinant of potential [[alcohol]] content, as these sugars serve as substrates for [[yeast]] during [[fermentation]].<ref>Jackson, ''Wine Science: Principles and Applications'' | Sugars in grapes are produced through [[photosynthesis]] and accumulate primarily as glucose and fructose during ripening. [[Sugar]] concentration is a key determinant of potential [[alcohol]] content, as these sugars serve as substrates for [[yeast]] during [[fermentation]].<ref>PhD Jackson, Ronald S., ''Wine Science: Principles and Applications'', Academic Press Inc, 14 April 2020. ISBN 9780128161180.</ref> | ||
Rates of sugar accumulation are influenced by climate, [[canopy]] function, crop load and harvest timing. Excessive sugar levels may lead to high alcohol wines, while insufficient accumulation can result in under-ripe styles. | Rates of sugar accumulation are influenced by climate, [[canopy]] function, crop load and harvest timing. Excessive sugar levels may lead to high alcohol wines, while insufficient accumulation can result in under-ripe styles. | ||
== Organic acids == | == Organic acids == | ||
The principal organic acids in grapes are [[tartaric acid]] and [[malic acid]]. Tartaric acid is largely stable throughout ripening, while malic acid declines as berries respire, particularly in warm conditions.<ref>Boulton | The principal organic acids in grapes are [[tartaric acid]] and [[malic acid]]. [[[[Tartaric]] acid]] is largely stable throughout ripening, while malic acid declines as berries respire, particularly in warm conditions.<ref>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.</ref> | ||
The balance between these acids defines grape and wine acidity, affecting freshness, microbial stability and [[ageing potential]]. | The balance between these acids defines grape and wine acidity, affecting freshness, microbial stability and [[ageing potential]]. | ||
== Phenolic compounds == | == Phenolic compounds == | ||
Phenolics include tannins, anthocyanins and flavonols, located mainly in the skins and seeds. These compounds influence colour, bitterness, astringency and antioxidant capacity in wine.<ref>Waterhouse | Phenolics include tannins, anthocyanins and flavonols, located mainly in the skins and seeds. These compounds influence colour, bitterness, astringency and antioxidant capacity in wine.<ref>Andrew L. Waterhouse, ''Understanding Wine Chemistry'', Wiley, 19 Aug. 2016. ISBN 9781118627808.</ref> | ||
Phenolic maturity does not always coincide with sugar ripeness, making harvest decisions critical for [[red wine]] styles where extraction is significant. | [[Phenolic maturity]] does not always coincide with sugar ripeness, making harvest decisions critical for [[red wine]] styles where extraction is significant. | ||
== Aroma and flavour precursors == | == Aroma and flavour precursors == | ||
Many grape-derived aromas exist as non-volatile precursors that are transformed during fermentation and ageing. These include terpene glycosides, norisoprenoids and thiol precursors, which are particularly important in aromatic varieties.<ref>Jackson, ''Wine Science: Principles and Applications'' | Many grape-derived aromas exist as non-volatile precursors that are transformed during fermentation and ageing. These include terpene glycosides, norisoprenoids and thiol precursors, which are particularly important in aromatic varieties.<ref>PhD Jackson, Ronald S., ''Wine Science: Principles and Applications'', Academic Press Inc, 14 April 2020. ISBN 9780128161180.</ref> | ||
The expression of varietal character depends on both grape composition at harvest and winemaking choices that preserve or enhance these compounds. | The expression of varietal character depends on both grape composition at harvest and winemaking choices that preserve or enhance these compounds. | ||
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== Factors influencing composition == | == Factors influencing composition == | ||
Grape composition is shaped by a combination of genetic and environmental factors, including grape variety, [[climate]], [[soil]], [[vine vigour]], crop load and harvest timing.<ref> | Grape composition is shaped by a combination of genetic and environmental factors, including grape variety, [[climate]], [[soil]], [[vine vigour]], crop load and harvest timing.<ref>Glen Creasy, Leroy Creasy, ''Grapes'', CABI Publishing, November 1, 2025. ISBN 9781800627048.</ref> [[Vineyard]] practices such as [[irrigation]], [[canopy management]] and yield control further influence berry development and final composition.<ref>UC Davis, “Berry development and composition”.</ref> | ||
Understanding these interactions is central to managing quality and achieving stylistic objectives in winemaking. | Understanding these interactions is central to managing quality and achieving stylistic objectives in winemaking. | ||