Science
Terpenes and floral aromatics
Grape-derived compounds behind the rose, lychee and citrus-blossom character of Muscat, Gewürztraminer and Riesling.
The short answer
Terpenes are grape-derived aroma compounds responsible for much of the floral and citrus character in aromatic white varieties. Unlike fermentation esters they come from the fruit, and much of the total is present as odourless bound precursors that release slowly.
Overview
Terpenes are what people usually mean by an "aromatic" variety, and they are among the best-characterised aroma compounds in wine.
The same compound family occurs throughout the plant world — linalool in lavender and coriander, geraniol in roses and geraniums — which is why the descriptors are so recognisable.
How it works
The mechanism, at the scope it has actually been established.
Monoterpenes accumulate in the grape during ripening, concentrated in and just beneath the skin. Skin contact before pressing is therefore associated with higher extraction, which is one reason a short pre-fermentation maceration is common for aromatic whites.
A substantial fraction exists as glycosides — terpenes bound to sugar molecules, which are odourless. These hydrolyse slowly under acidic conditions and can be released enzymatically, so aroma continues to develop after fermentation.
The principal compounds are linalool, geraniol, nerol, citronellol and α-terpineol, associated respectively with characters ranging from citrus blossom and rose through to lime.
Concentration is generally higher in Muscat varieties, Gewürztraminer, Riesling, Torrontés and Moscato, which is what groups them together as a category.
Excessive heat and prolonged skin contact can shift the balance towards compounds associated with less attractive characters, which is one reason aromatic whites are handled cool and pressed gently.
Compounds named on this page
Where a compound comes from is chemistry; what it smells like is perception. These are kept apart deliberately.
- Terpenes
- Grape-derived compounds behind floral and citrus character in aromatic varieties. Associated with rose, lychee, citrus blossom, lime, geranium.
Sources
Sources consulted
- The Australian Wine Research Institute — AWRI
- UC Davis Department of Viticulture and Enology — University of California, Davis
- The Oxford Companion to Wine — Oxford University Press
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