Science
Rotundone and peppery Syrah
A single compound that accounts for black-pepper aroma — and which around a fifth of people cannot smell at all.
The short answer
Rotundone is a sesquiterpene identified as the compound responsible for black-pepper aroma in wine. It is unusual in being a rare case where one compound accounts for one descriptor, and equally unusual in that a substantial proportion of people are specifically unable to smell it.
Overview
Rotundone was identified in Australian Shiraz in the 2000s, and it is the same compound that makes black peppercorns smell of pepper.
It is the best documented case of specific anosmia in wine, which makes it a useful reminder that tasting notes describe an interaction rather than a property.
How it works
The mechanism, at the scope it has actually been established.
Rotundone accumulates in grape skins late in ripening. Cooler conditions during the ripening period are associated with higher concentrations, which is the mechanism usually cited for peppery character being more prominent in cooler-climate Syrah.
It is present in some other varieties, including Grüner Veltliner, Duras, Mourvèdre and Vespolina, and in peppercorns, marjoram and rosemary.
It is extracted from skins during maceration, so extraction decisions influence how much reaches the wine.
Published sensory thresholds are around 16 nanograms per litre in red wine, though the figure varies with matrix.
Around a fifth of tasters in published studies could not detect it even at high concentrations. For those people the wine genuinely does not smell peppery, and neither party is mistaken.
Why it matters in the glass
It gives a real, checkable answer to a real question — why Northern Rhône Syrah so often reads peppery and Barossa Shiraz so often does not — without resorting to vague appeals to terroir.
Compounds named on this page
Where a compound comes from is chemistry; what it smells like is perception. These are kept apart deliberately.
- Rotundone
- The compound responsible for black-pepper aroma — and one many people cannot smell. Associated with black pepper. Around 16 nanograms per litre in red wine in published studies, with the figure varying by matrix. Around a fifth of tasters in those studies could not detect it at any concentration tested. Caution: The best-documented specific anosmia in wine. Two people can disagree about whether a Syrah is peppery and both be reporting accurately.
The relationship with temperature is well supported but not simple. Site, vintage, ripeness and clone all bear on concentration, and a warm-climate Syrah is not incapable of showing pepper.
Sources
Sources consulted
- Research on rotundone, the peppery aroma compound in Syrah — Peer-reviewed oenological literature
- The Australian Wine Research Institute — AWRI
- Wine Australia — regions, GIs and market information — Wine Australia
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