Terpenes
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.[1]
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
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.[2]
In grapes and wines, terpenes may exist in two principal forms:
- 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.[3]
Origin and biosynthesis
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.[4]
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
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.[5]
In less aromatic varieties, terpenes may still be present at sub-threshold levels, contributing subtly to complexity rather than overt aroma.
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.[6]
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
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.[7]
At low concentrations, terpenes enhance freshness and finesse; at excessive levels, they may appear perfumed or overpowering, depending on stylistic context.[8]
Stability and evolution
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.[9]
Proper oxygen management and temperature control are therefore critical to preserving terpene-driven aromas.
Terminology and analysis
Terpenes are a recognised category within international oenological terminology and aroma classification systems.[10]
They are routinely measured and studied in wine aroma research, with practical guidance provided by academic and industry institutions.[11][12][13]
Cultural and stylistic context
Aromatic intensity derived from terpenes plays a significant role in shaping consumer expectations and stylistic identity, particularly in wines marketed for freshness and expressiveness. The global dissemination of aromatic styles has reinforced the prominence of terpene-driven wines in international markets.[14]
The perception and language of aroma, including terpene-associated descriptors, are also shaped by cultural context and tasting conventions.[15]
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 9780198705383.
- ↑ Jackson, Wine Science: Principles and Applications, Academic Press, 2020, ISBN 9780128161180.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Volume 2, Wiley, 2006, ISBN 9780470010396.
- ↑ Keller, The Science of Grapevines, Academic Press, 2015, ISBN 9780124199873.
- ↑ Robinson, Harding & Vouillamoz, Wine Grapes, HarperCollins, 2012, ISBN 9780062206367.
- ↑ Waterhouse, Sacks & Jeffery, Understanding Wine Chemistry, Wiley, 2016, ISBN 9781118627808.
- ↑ Stevenson, The Sotheby’s Wine Encyclopedia, DK, 2011, ISBN 9780756686840.
- ↑ MacNeil, The Wine Bible, Workman, 2022.
- ↑ Ribéreau-Gayon et al., “Aroma compounds of grapes and wines”, American Journal of Enology and Viticulture, ISSN 0002-9254.
- ↑ OIV, “Aromatic compounds in wine”, https://www.oiv.int
- ↑ UC Davis, “Terpenes and wine aroma”, https://wineserver.ucdavis.edu
- ↑ AWRI, “Aroma chemistry”, https://www.awri.com.au
- ↑ FAO, “Grape aroma compounds”, https://www.fao.org
- ↑ Anderson & Pinilla, Wine Globalization, Cambridge University Press, 2018, ISBN 9781108445687.
- ↑ Charters, Wine and Society, Elsevier, 2006, ISBN 9780750669788.