It isn’t uncommon to question the complex descriptions of wine flavors and aromas – can one genuinely detect the scent of grass, grapefruit, rose, and pepper in a glass of wine? The answer, surprisingly, is yes. Let us investigate into the science behind this.
The key to understanding this lies in organic chemistry. Grapes, like all fruits and plants, rely on a shared pool of elements. In unfermented grapes, most aroma molecules are tied up with sugar, rendering them undetectable to our noses. However, the process of fermentation, which converts sugar to alcohol, liberates these volatile flavor compounds and makes them perceptible to our olfactory sense.
Some of these aromas directly originate from the grapes and are similar to the compounds found elsewhere in nature, like the terpenes in Riesling and citrus peel. Some aromas, known as esters, are the byproducts of fermentation, while others evolve as the wine ages and its constituents interact. Further complexities are added by oak and other winemaking practices, infusing compounds that hint at vanilla, caramel, or coconut.
Several factors contribute to the intricate labyrinth of aromas we encounter every time we inhale the scent of wine. Depending on our sensitivity and the concentration of the compounds, our brains are capable of decoding many of these aromas.
Here, we delve into some significant compounds found in wine and their associated aromas and flavors that might surprise you.
Terpenes
The presence of rose petals or citrus in your wine’s aroma is attributed to terpenes, predominantly found in grape skins and plentiful in nature – in flowers, fruits, and leaves of various plants.
Terpenes are a category of compounds that make wines like Muscat and Gewürztraminer aromatic and impart characteristic citrus notes to Riesling. Here are some familiar ones.
Linalool: In conjunction with other compounds, this terpene induces the perception of lavender, orange blossom, lily, and even bay leaves.
Geraniol: The compound responsible for the distinctive smell of rose petals.
Nerol and citronellol: These compounds give rise to the floral, citrusy fragrances found in numerous flowers, fruits, and wines.
Limonene and citral: The tangy flavors in wine come from the same compound present in citrus peel.
Hotrienol: The aroma of linden blossom, which also contributes to the intense elderflower smell in Sauvignon Blanc, comes from this compound
1,8-cineole and alpha-pinene: When you whiff the aroma of eucalyptus in red wines from Australia or the distinct scent of garrigue shrubland in red wines from Southern France, it’s due to the presence of 1,8-cineole and alpha-pinene. The former contributes the unique eucalyptus aroma, while the latter is found in fragrant shrubs such as juniper and rosemary. These volatile aroma compounds are airborne and can latch onto the bloom of grape skins.
Rotundone: This sesquiterpene is responsible for the peppery aroma found in Shiraz, Syrah and Grüner Veltliner. In fact, rotundone is the same compound that lends the potent fragrance to peppercorns, especially white pepper.
Aldehydes
Hexanal and hexenal: Freshly cut grass and tomato leaf scents in Sauvignon Blanc originate from these two aldehydes.
Vanillin: This is the principal flavor of vanilla beans and is also found in wines as a result of fermentation or aging in oak barrels. American oak, or Quercus alba, tends to have a higher vanillin content than French oak or Quercus robur. Therefore, it’s no surprise if a California Zinfandel aged in American oak barrels has a distinct vanilla aroma.
Benzaldehyde: The scent of bitter almond or marzipan in matured Pinot Gris or certain Italian white wines can be credited to this compound.
Furfural: This compound, reminiscent of dried wood, caramel, and wheat bran, is commonly found in wines aged in oak barrels.
Pyrazines
Methoxypyrazines: If you have ever sensed the aroma of green bell pepper in Cabernet Sauvignon or a leafy note in Carmenère, you are detecting methoxypyrazines. These enduring compounds are part of the characteristic profile of certain grapes, particularly those in the Sauvignon family.
Methoxypyrazines may also suggest underripeness in some grape varieties, appearing as a sharp herbaceous note.
Esters
Esters are fleeting flavor compounds produced by the reaction between alcohols and acids. They provide the primary fruit flavors in very young wines.
Isoamyl acetate and ethyl acetate: These common esters are responsible for the pear-drop candy, banana, and pear aromas often found in youthful white wines
Octyl acetate: This ester imparts orange and citrus fruit aromas.
Butyl acetate: This ester is responsible for the scent of Red Delicious apples in wines.
Ketones and Diketones
Beta-ionone: This compound imparts the distinct violet aroma in Pinot Noir or Syrah.
Beta-damascenone: This ketone is behind the wine’s floral fragrances with a hint of red fruit.
Diacetyl: As the most noticeable diketone, diacetyl has a melted butter aroma, and may present as creaminess in the wine. Diacetyl is a side product of a process called malolactic fermentation where sharp malic acid in wine is converted into a much milder lactic acid. This is the reason why many Chardonnays have a buttery and creamy aroma. Chardonnay that has undergone malolactic fermentation and is subsequently aged in fresh American oak, which gives it vanilla and nutty scents, can be compared to buttered popcorn.
