Science
TDN: the petrol note in Riesling
A compound that accumulates as Riesling ages, associated with sunlight and water stress in the vineyard — and divisive rather than faulty.
The short answer
TDN — 1,1,6-trimethyl-1,2-dihydronaphthalene — is a norisoprenoid that develops in bottle from precursors laid down in the grape. It is associated with kerosene and petrol descriptors, it accumulates with age, and it is a normal feature of mature Riesling rather than a fault.
Overview
Few aromas divide drinkers as sharply. Experienced Riesling drinkers frequently treat it as a marker of proper maturity; newcomers often find it alarming.
It is a genuine case where preference varies rather than where one party is mistaken.
How it works
The mechanism, at the scope it has actually been established.
Carotenoid compounds in the grape are broken down into norisoprenoid precursors during ripening. These are stored in the grape in bound form.
Over time in bottle, acid-catalysed hydrolysis releases TDN, so concentration rises with age. Warmer storage accelerates the process.
Precursor levels are associated with higher sunlight exposure on the fruit, water stress and elevated temperature during ripening — so vineyard conditions influence how much potential is there before the wine is even made.
Sensory thresholds reported in the literature are in the low micrograms per litre, and vary with the wine.
Some producers actively manage it, using canopy shading, harvest timing and closure choice — screwcap liners with different oxygen transmission are associated with different rates of accumulation.
What people get wrong
1 widely repeated claim this page corrects.
Compounds named on this page
Where a compound comes from is chemistry; what it smells like is perception. These are kept apart deliberately.
- TDN — 1,1,6-trimethyl-1,2-dihydronaphthalene
- The compound behind the petrol note in aged Riesling. Associated with petrol, kerosene, paraffin. Caution: Not a spoilage compound and not an indicator of a fault. Preference for it genuinely divides drinkers.
Sources
Sources consulted
- The Australian Wine Research Institute — AWRI
- Deutsches Weininstitut (German Wine Institute) — DWI
- The Oxford Companion to Wine — Oxford University Press
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