Guest Post by Nicolas Quillé MW: Why do some white wines smell of petrol? - WineUncorked: Wine Reviews and Tips

Petrol notes are often found in aged wines made from grape varieties that are rich in a group of chemicals called terpenes. Muscat, Riesling, Gewurztraminer and Torrontes all have high concentrations of the terpenes nerol, linalool and geraniol. Terpenes can add other intense aromatic fragrances to the grapes and these can smell pleasantly of roses and citrus fruits.

Terpene concentration in grapes is increased by a high level of ultra violet (UV) light exposure on the grape berries. So some grape growers use wine growing techniques to increase the amount sunlight on their fruit.

The increase in UV light promotes the formation of terpenes along with other molecules such as carotenoids (which also causes the orange pigment in carrots). Carotenoids and terpenes share a similar chemical starting point, which during the wine aging process form a compound named 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN). TDN is the compound responsible for the petrol smell.

It is the initial concentration of these starting chemicals which determines the wine’s potential to develop TDN and petrol notes over time.

Factors that are likely to increase TDN in grapes are:

High light exposure

Ripe grapes (accentuated by low yields and/or late harvest)

Water stress (which is most likely in regions that don’t practice irrigation)

Warm soils (grape vines growing in gravel for example)

This primarily occurs in dry vineyard sites during warm and low-rain years.

These factors are usually also considered to contribute to high-quality grapes which is why many high quality terpene rich wines are also rich in petrol notes.

Nicolas Quillé is a Master of Wine and so uses the accredited term 'MW' after his name. He is also Chief Winemaking and Operations Officer for the Crimson Wine Group. 

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