Everyday Olfactics: The Wine Edition
Posted 27th Apr 2017You’ve smelt it so many times before and it seems so familiar, but what is it? In this ‘Everyday Olfactics’ we delve into those familiar smells to unearth their sometimes less familiar origins.
As enthusiastic sommeliers all over the world will know, putting emphasis on how you smell your wine is not to be ‘sniffed’ at (sorry)! While our nose is hovering over the glass, short quick sniffs are much more preferable to long large sniffs just as when we are smelling fragrances. This is because the alcohol content of a scent can fatigue the nose easily, which in turn renders it ineffective more quickly during those large inhalations.
From the grape vine to the wine glass, a number of prominent aromas develop at varying stages. One of which is the interesting, spicy and certainly noteworthy, sesquiterpene molecule Rotundone (C15H22O). This molecule holds a distinctive aroma for many grape species, it is found only in the skin of the grape and referred to as a primary aroma as it is present even before the production of wine has commenced. Rotundone is also present in black pepper, marjoram, oregano, rosemary, basil, thyme, and geranium, which is why we can pick out those all too acquainted notes.
Our good old friend Rotundone packs quite a punch in even the smallest of quantities, being detectable at 16ng/L or 0.000000016g per litre or… 0.04g in an Olympic swimming pool full of wine. Its strong old stuff, it’s presence is even more detectable in water requiring only 0.02g in the same pool full of H2O, I think I’ll take the pool full of wine thanks! Of all the wines Rotundone is most prominent in the darker reds as the molecule alongside the pigmentation diffuses from the skin during fermentation. Hence, Whites and Rosés that have had their skins removed early on in the manufacture process have a lessened opportunity for this diffusion to take place (think red Rioja compared to white Rioja).
If you fancy appraising a bottle for yourself, we can recommend Shiraz as the wine highest in Rotundone. The molecule naturally occurs at higher concentrations in Shiraz grapes than any other varieties, contributing to the characteristic spiciness. Don’t mind if we do.
-The aromatic molecular makeup of a grape before being picked is often vastly different to that of the subsequent wine that has fermented and been aged.
Moving through the production process, terpenes such as Geraniol, Linalol and Nerol come forth. The scents from these molecules are known as secondary aromas because they exist at below quantifiable levels in the natural grape but at more easily detectable levels during and after fermentation. In wines these three wonderful molecules present themselves (as expected) as floral notes such as Lavender, Neroli, Rose, Geranium and so on. For a more comprehensive look into the floral notes of specific wines I recommend the illustration here: http://winefolly.com/tutorial/common-flower-aromas-in-wine/ .
Further changes can be noted when aroma compounds are transformed for a third time during the aging process, when the molecules once bound to sugars are separated. This allows the aroma to be released, allowing the wines to really develop their individual personalities (complex chemical reactions can improve the mouth feel, flavour and aroma of the wine in many cases). The organic compound Vanillin is produced through the degradation of lignin during oak barrel aging; this is a great example of how aging can make wine more pleasing for the taster, creating a smooth mouthfeel and creamy aroma. Chemical compounds known as Raspberry ketone and Damascenone are further examples of these tertiary aromas and are the scents involved in the wine’s bouquet; which specifically refers to smells which arise from the chemical reactions of fermentation and aging of the wine. By definition a wines ‘bouquet’ is also inclusive of the subsequent results of oxidation and the final changes that take place while the wine rests in its bottle.
The final stages of aging aren’t all good and unfortunately in some cases if a wine is left to rest for too long the process can lead to the formation of Dimethyl sulphide, a molecule also found after fermentation in ale and lager. The longer a wine is aged the greater the aroma molecules potential prominence and with an undiluted odour of cabbage, too much Dimethyl sulphide and the wine will smell off.
Whilst we are on the topic of smelling off … corked wine lets off a chemical compound known as 2,4,6-trichloroanisole (TCA). Compared by Mary Orlin (the award winning WineFashionista) to “wet newspaper, dank basement, wet shaggy dog and musty”. TCA is a fungal metabolite used as a fungicide in cork (that’s how it sneaks into your glass of Pinot), it’s detectable at 25ng/L which is 0.063g in our Olympic swimming pool, that’s still tremendously strong and although it may not harm your health, the potency is a good enough reason to put your Pinot down.
Aside from wine itself, familiar wine aromas are prevalent elsewhere. Take your pick from Shiraz scented candles with added Bergamot and Orange notes, fine fragrances consisting of wine itself and Prosecco scented soap. We’ll say cheers to that!
References
https://winesociety.stanford.edu/why-wine-smells-way-it-does
http://www.huffingtonpost.com/mary-orlin/bad-wine-aromas-_b_873803.html
https://en.wikipedia.org/wiki/2,4,6-Trichloroanisole