In my experience, questions about wine aromas are asked in three steps:
Step one: “Can people really smell those aromas or you guys just made them up?”
If I manage to convince the asker the aromas really do exist, then…
Step two: “Are they from the wine itself? Or does the winemaker soak roses or jasmines into the wine to create those aromas?”
“They are from the wine.”
Skeptical but getting curious, the asker digs deeper…
Step three: “Then how do these aromas come about?”
The answer lies in the magic of fermentation and maturation.
Not only does fermentation turns grape sugar into alcohol, it also turns many aroma compounds inherent in grape berries from imperceptible to perceptible. For example, the intense lychee aroma in a Gewürztraminer that gets many wine lovers hooked comes from a compound called rose oxide, which does exist in the grape, but the aroma intensity the compound shows in the grape is way lower than that in the wine when fermentation is done. Compounds 3MHA and 4MMP in the Sauvignon Blanc grape are also made more discernible through the reaction of fermentation, giving the wine aromas of passion fruit and elderflower respectively. The peppery aroma in Syrah and Grüner Veltliner granted by the compound rotundone is also made more detectable than in the grape via fermentation. And the reason why these compounds give off aromas like lychee, passion fruit, elderflower and pepper is exactly because they also exist in the aforementioned fruits, flower and spice.
The wine aromas intrinsic to the grape and enhanced by fermentation are collectively called “primary aromas”. And since there are primary ones, you bet secondary aromas are also around.
Secondary aromas are those created by a couple of winemaking steps other than fermentation, such as malolactic conversion, oak maturation and lees ageing. Malolactic conversion, common in red winemaking and sometimes used in white winemaking, is to convert tart malic acids into smoother lactic acids, rounding a wine’s sharp edges, making it more pleasant to drink. Depending on the conversion method used, in some cases, not only does malolactic conversion create lactic acids, it also produces diacetyl, a compound that gives a buttery aroma, which is usually preferred in a fuller-bodied Chardonnay.
Then comes oak maturation. Not all wines go through this step but for those which do, depending on what oak is used, the wines may gain aromas like vanilla, baking spices or even coconut. In general, French oak barrels tend to give more vanilla (compound: vanillin) and baking spice (compound: eugenol) notes to the wine, as in a Bordeaux, while American oak barrels tend to give the coconut aroma (compound: oak lactone) to the wine, as in a Rioja. Oak type aside, it is the newness and the size of the barrel that determines the intensity of these oak-derived aromas ending up in the wine. The newer and the smaller the barrel in which the wine is matured, the more intense the aroma compound will show in the final wine.
In the case of lees ageing, with the passing of time, lees will break down releasing a bready aroma (compound: aldehydes) into the wine.
If secondary aromas are a thing, the existence of tertiary ones shouldn’t be surprising us here.
Simply put, tertiary aromas is what a wine gains when kept in an oxidised environment for a period of time. This oxidised environment can be inside an oak barrel or inside a bottle. Oak is watertight but breatheable, so oak maturation allows gentle oxidation in the wine. And so does bottle ageing, because small amount of air can still penetrate through the pores of the cork. Gentle oxidation over time can give wine some air-dried, concentrated characters, such as the shiitake mushroom aroma (compound: 1-octen-3-ol) in red wines and the dried apricot aroma (compound: gamma-decalactone) in white wines.
White wines like Riesling and Timorasso after a period of bottle ageing can even develop a petroleum-like aroma, based on a compound named TDN. However, in the case of TDN, natural cork tends to absorb it quite effectively. For winemakers who wish a prolonged petroleum-like aroma in their Riesling or Timorasso, they’d probably prefer the use of screwcaps.
Aromas can be secondary or tertiary, just as oxidation can be gentle or aggressive. For wines subject to aggressive oxidation such as Oloroso (matured under a headspace inside the barrel), with time, walnut and caramel aromas will develop in the wine. While the compound sotolon is resposible for the walnut aroma, it is the compound furaneol that adds a layer of caramelised nuance to the wine.
Now as the task of writing this article comes to an end, I’d like to pour myself a glass of delightful lychee perfume, made 100% from grapes, no lychees involved at all.
Wine is just full of wonder, isn’t it?
And don’t worry, there are no quaternary aromas, yet.
