Terpenes: Difference between revisions
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''' | '''Terpenes''' are a class of volatile aromatic compounds that play a central role in the sensory profile of many wines, particularly those produced from so-called aromatic grape varieties. They are primarily responsible for floral, citrus, and herbal notes perceived in grape-derived aromas and are therefore considered part of a wine’s primary aroma spectrum.<ref>Robinson (ed.), ''The Oxford Companion to Wine'', Oxford University Press, 2015, ISBN 9780198705383.</ref> | ||
In wine chemistry, terpenes are of particular interest because they originate largely in the grape itself rather than being formed during | In wine chemistry, terpenes are of particular interest because they originate largely in the grape itself rather than being formed during fermentation or ageing. | ||
== Chemical nature and classification == | == Chemical nature and classification == | ||
Terpenes are hydrocarbons constructed from isoprene units and occur in wine mainly as monoterpenes. Common wine-relevant terpenes include linalool, geraniol, nerol, citronellol, and α-terpineol, each contributing distinct aromatic impressions.<ref>Jackson, ''Wine Science: Principles and Applications'', Academic Press, 2020, ISBN 9780128161180.</ref> | Terpenes are hydrocarbons constructed from isoprene units and occur in wine mainly as monoterpenes. Common wine-relevant terpenes include linalool, geraniol, nerol, citronellol, and α-terpineol, each contributing distinct aromatic impressions.<ref>Jackson, ''Wine Science: Principles and Applications'', Academic Press, 2020, ISBN 9780128161180.</ref> | ||
In | In grapes and wines, terpenes may exist in two principal forms: | ||
* '''Free terpenes''', which are directly aromatic and perceptible. | * '''Free terpenes''', which are directly aromatic and perceptible. | ||
* '''Glycosidically bound terpenes''', which are non-volatile and odourless until hydrolysed during fermentation, ageing, or enzymatic activity.<ref>Ribéreau-Gayon et al., ''Handbook of Enology, Volume 2'', Wiley, 2006, ISBN 9780470010396.</ref> | * '''Glycosidically bound terpenes''', which are non-volatile and odourless until hydrolysed during fermentation, ageing, or enzymatic activity.<ref>Ribéreau-Gayon et al., ''Handbook of Enology, Volume 2'', Wiley, 2006, ISBN 9780470010396.</ref> | ||
== Origin and biosynthesis == | == Origin and biosynthesis == | ||
Terpenes are synthesised in the grape berry via metabolic pathways active in the skins, with concentrations influenced by | Terpenes are synthesised in the grape berry via metabolic pathways active in the skins, with concentrations influenced by variety, vineyard site, climate, and viticultural practices.<ref>Keller, ''The Science of Grapevines'', Academic Press, 2015, ISBN 9780124199873.</ref> | ||
Sun exposure, | Sun exposure, temperature, and berry maturity all affect terpene accumulation. Moderate sunlight generally promotes terpene synthesis, while excessive heat may reduce aromatic retention. | ||
== Role in grape varieties == | == Role in grape varieties == | ||
Terpenes are especially prominent in aromatic grape varieties, where they define varietal | Terpenes are especially prominent in aromatic grape varieties, where they define varietal typicity. Muscat varieties are the most terpene-rich, but significant terpene expression is also found in grapes such as Riesling and Gewürztraminer.<ref>Robinson, Harding & Vouillamoz, ''Wine Grapes'', HarperCollins, 2012, ISBN 9780062206367.</ref> | ||
In less aromatic varieties, terpenes may still be present at sub-threshold levels, contributing subtly to | In less aromatic varieties, terpenes may still be present at sub-threshold levels, contributing subtly to complexity rather than overt aroma. | ||
== Winemaking influences == | == Winemaking influences == | ||
Winemaking choices strongly influence terpene expression in the finished wine. Factors such as skin contact, fermentation temperature, yeast selection, and enzyme use can enhance or suppress terpene release from bound precursors.<ref>Waterhouse, Sacks & Jeffery, ''Understanding Wine Chemistry'', Wiley, 2016, ISBN 9781118627808.</ref> | |||
Cool fermentation temperatures generally preserve terpene volatility, while oxidative handling can lead to aroma loss. Certain yeast strains exhibit greater glycosidase activity, promoting terpene liberation during fermentation. | Cool fermentation temperatures generally preserve terpene volatility, while oxidative handling can lead to aroma loss. Certain yeast strains exhibit greater glycosidase activity, promoting terpene liberation during fermentation. | ||
== Sensory contribution == | == Sensory contribution == | ||
Terpenes are typically associated with floral (rose, | Terpenes are typically associated with floral (rose, orange blossom), citrus (lemon peel), and herbal notes. Their sensory impact depends on concentration, matrix effects, and interaction with other aroma compounds.<ref>Stevenson, ''The Sotheby’s Wine Encyclopedia'', DK, 2011, ISBN 9780756686840.</ref> | ||
At low concentrations, terpenes enhance freshness and finesse; at excessive levels, they may appear perfumed or overpowering, depending on stylistic context.<ref>MacNeil, ''The Wine Bible'', Workman, 2022.</ref> | At low concentrations, terpenes enhance freshness and finesse; at excessive levels, they may appear perfumed or overpowering, depending on stylistic context.<ref>MacNeil, ''The Wine Bible'', Workman, 2022.</ref> | ||
== Stability and evolution == | == Stability and evolution == | ||
Terpenes are relatively sensitive to | Terpenes are relatively sensitive to oxidation and ageing. Over time, free terpenes may degrade or transform into less aromatic compounds, contributing to the gradual loss of primary fruit character in aged wines.<ref>Ribéreau-Gayon et al., “Aroma compounds of grapes and wines”, ''American Journal of Enology and Viticulture'', ISSN 0002-9254.</ref> | ||
Proper | Proper oxygen management and temperature control are therefore critical to preserving terpene-driven aromas. | ||
== Terminology and analysis == | == Terminology and analysis == | ||