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Sniffing Out the Secrets of White Wine Aroma

©Richard Gawel

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A quick glance through some of the popular wine articles in magazines and newspapers would leave most people perplexed. Descriptions of wines in terms of things such as grandmothers drawers, cobblers tar, drenched dogs, cats wee and the like leave many people with the distinct impression that either wine tasting is difficult, or that the people using such terms are very imaginative.

Notwithstanding the fact that wine journos need to be entertainers as well as being informative, there are good reasons that so many terms have been used to describe wines. Wine in its least romantic sense is a complex cocktail of naturally occurring chemical substances or compounds. Early estimates put the number of compounds in wine at around 800, but there is undoubtedly many more numbering in the thousands or perhaps even the tens of thousands. Many of these compounds contribute to the aroma and flavour of wine.

When you sniff a wine and savior its aromas you are in fact sampling from the 'invisible soup' of substances that float around in the headspace of the wineglass. Some of the compounds in this soup are very odour active and are known as wine character impact compounds. When you smell these compounds in their pure form they immediately conjure up distinct impressions of a particular flower or other type of fruit. Examples are, the lemony linalool (in Riesling), and the capsicum like 2-methoxy-3-isobutylpyrazine (in Sauvignon Blanc). Other compounds are subtler in their contribution. These are known in the other great aroma domain of perfumery as congeners and diversifiers. Congeners enhance other aromas and 'fuse' them into new complex and seamless scents. Diversifyers add 'notes' and nuances to existing aromas making them complex and interesting. In the wine world, candidates for such compounds are damascanone and alpha ionone (both found in Chardonnay). Damascanone has an almost narcotic scent of exotic flowers with a heavy fruity undertone while alpha ionone has an alluring violet like aroma. Whilst being single compounds they often display multiple aromas that fade in and out with your passing attention. For this reason these substances probably play a large role in the fruit complexity of great Chardonnay wines.

All the compounds and associated wine aromas mentioned above come from the grape, and as such are known as varietal characters. There are too many others to mention here, but one is rather fascinating. Cats urine does exist in wine! Well its smell anyway. Caused by the Dr Jekyll and Mr Hyde compound p-mentha-8-thiol-3-one, this sulfur containing compound smells exactly like cat's urine when in a particular concentration range. When weaker, it exudes the herbal scent of lantana bush, whilst when strong, it has an aroma that can be likened to blackcurrants. And where do you find it? That's right, in the variety where wine tasters see it the most, Sauvignon Blanc and Cabernet Sauvignon (and of course in cat's urine).

Other wine aromas and flavours derive from the chemical by-products of yeast fermentation. These aromas are often distinctly in the fruity part of the aroma spectrum and include banana, pineapple, passionfruit and apple. They derive from a class of compounds called esters, which incidentally give most fruits their characteristic aromas and flavours.

When a wine ages, typically both its varietal and fermentation characters will fade and will be replaced by a raft of other substances that develop in the wine over time. While less is known about these compounds, a few have been identified. The most important substance associated with aged Riesling is the impressively named 1,6 trimethyl-1,2-dihydronaphalene (or TDN). If you have tasted an aged keroseney Riesling lately then you would have tasted TDN first hand. Another compound that scientists are beginning to get a handle on is the mouth-watering compound called sotolon. Sotolon reeks of toffee apples and maple syrup and contributes to the aged character of some white wines and surprisingly is always found in the great flor Sherries.

Lists of wine characters by variety and winemaking practice can be found elsewhere on this site (free of course). Click here.

But don't forget that wine is there to be enjoyed. Somehow though, the more you learn about wine the more you tend to enjoy it. But why not keep a list of wine descriptors handy at your next wine tasting. You never know, you may get a whiff of your grandmothers drawers in some obscure Jerezian amontillado. But sometimes it is better keeping some things to yourself!