DipWSET Theory: Aromatic Compounds

1. Aromas from grapes

Grapes come with their own aromatic compounds. Examples include:

• Metoxypyrazines—example: the capsicum-like aroma in Sauvignon Blanc, Cabernet Franc, and Cabernet Sauvignon

 

• Rotundone—example: a white pepper-like aroma, most prominently found in Gruner Veltliner

2. Aromas created by fermentation due to aroma precursors in the grape/grape must

Aroma precursors are non-aromatic compounds found in grapes that become aromatic during the fermentation process. So, for example, non-aromatic guy A bumps up against fermentation-compound dude B and together they create something that smells reminiscent of a wine aroma. Examples include:

• Thiols—ie that “box tree” aroma in Sauvignon Blanc
• Terpenes—ie that super floral perfumey aroma in Muscat

3. Aromas from fermentation process and fermentation by-products

The process of fermentation creates reactions between acids and alcohols; incorporates oxygen; yeast can create their own compounds; and then there are the by-products of the fermentation process—the dead yeast cells, aka lees. Fermentation is a busy process that can, indeed, create aromas we can then sense in the resulting wine. Examples include:

• Esters—created from the reaction of acids and alcohols; you’ll recognize them as the “fresh, fruity aromas” in young white wines, like apple, pineapple, etc.
• Acetaldehyde—created when ethanol (alcohol) comes into contact with oxygen; this actually MASKS fresh fruit aromas, as in Fino Sherry.
• Diacetyl—most commonly created during malolactic fermentation; it’s that buttery smell you may associate with California Chard
• Sulfur compounds—can be created by yeast in a reductive (non-oxygen) environment; creates a broad range of aromas from subtle matchstick of flint to rotten eggs (that’s when you know you’ve gone too far)

4. Aromas from “other sources”

Oak aging—especially new oak can contribute flavors like vanilla; aging in oak also introduces oxygen, which will further affect the wine

Environment—probably the most common example is eucalyptus found in wines from the AU where vineyards are really close to eucalyptus trees. In California, there’s argument that vineyards next to cannabis farms are also picking up on some of that *ahem* scent. And I heard one person say that their Semillon has a distinct “pomelo” aroma. Turns out the vineyard is next to a few pomelo trees. So…it happens.