The purpose of each of the charts below is to link the chemical causes of distinctive wine aromas to the potential descriptions we can use to describe these elements. Each class of aromatic compound is explained in more detail in our Science of Tasting Expanded Guide.

Special thanks to Madeline Puckette from Winefolly.com for working with us on these graphics.

Fruit, flower, and herb:

• Many fruity aromas and lightly floral tones are the result of esters. Esters are created by the interaction of acids and alcohol. They are often formed during fermentation and the specific yeasts and fermentation temperature may influence their character. Be careful not to confuse the lightly floral and fruity character of esters with the more distinctively aromatic terpenes.
• Terpenes—specifically monoterpenes—are a diverse category of highly aromatic organic compounds that are produced by the grapevines themselves. Muscat, Gewürztraminer, Torrontes, and Viognier are known to be particularly high in terpenes while Riesling and Albariño contain moderate levels.
• Pyrazines are responsible for many of the herbal aromas that we find in the Bordeaux varieties such as Sauvignon Blanc, Cabernet Sauvignon, Cabernet Franc, Carmenere, and Merlot. (Pyrazines in Malbec tend to be below the threshold of perception.) Be careful not to confuse their smell for that of stem inclusion. 
• Thiols are technically synonymous with Mercaptans—they easily capture mercury atoms—but we usually use the latter term to describe an onion or garlic faulty character, while we use thiol in reference to the grapefruit or passionfruit notes you are likely to find in a Sauvignon Blanc or Grüner Veltliner.

Earth:

Earthy aromas are perhaps the most complex to define in origin. They can be the result of microbial activity (often described as organic earth) as well as complex reduced sulfur compounds (often described as inorganic or mineral).  It was once assumed that earthy flavors made their way from the soil through the grapevine into the grape but modern science gives us a different—yet admittedly complex—picture.

• Geosmin is an organic compound with a notedly earthy smell. It is produced by bacteria and is a major component in the smell of wet rocks after a rain when these organic compounds are volatilized into the air. The transmission of geosmin into wine is likely the result of compounds being directly deposited on the skins of grapes rather than being transmitted through the vine. 
• Brettanomyces is a yeast that is naturally occurring and frequently found in a winery environment. An individual’s tolerance and taste for brett is highly subjective. It can be a defining character in many "old world" style wines as the result of a winery’s stylistic tolerance and not of any inherent terroir. 
• Volatile Acidity is a byproduct of microbial metabolism. Acetic acid bacteria (used to create vinegar) creates acetic acid, the most common form of VA. As it requires oxygen to grow, reductive environments and SO2 usage limit its presence. It can be a stylistically positive note in many classic oxidative wines such as Barolo or Rioja.
• When we think of sulfur and wine we are often assuming the elemental form of S02 that is added as an antimicrobial and anti-oxidant. However, many reduced sulfur compounds are created as the result of fermentation and other complex chemical interactions. Low nutrient musts and low pH environments (high acid) may encourage some forms of reduced sulfur that are often described as chalky or flinty and can be an important component of cool climate wines such as Chablis, Sancerre, German Riesling, and Champagne.

Spice:

The spice of wine can come from both varietal fruit character as well as the influence of winemaking and oak aging. Distinguishing between the two can be an important factor in blind tasting.

• While lactone esters can be present in grapes, their major impact in wine comes from oak aging. Vanilla, hazelnut, and coconut are common descriptors.
• Rotundone is an aromatic sesquiterpene (for you geeks, they have three isoprene units while our floral monoterpenes have two). It is most associated with the essential oils of peppercorns and culinary herbs like basil and thyme. Syrah and Grüner are the two most iconic grapes which are high in these compounds but other lesser-known varieties such as Mourvèdre may showcase this aroma. Winemaking techniques such as filtration can have a major effect on reducing their levels.
• Botrytis cinerea is a fungus that affects fruit following damp conditions. While most famous in sweet wines, they can also affect dry wines. Ginger, chamomile, honey, and saffron are telltale aromas and it is a common feature in the wines of Alsace, Austria, Germany, and the Loire Valley.
• While we have previously mentioned the effect of thiols in fruit driven aromas like grapefruit, these compounds can also be responsible for some meaty or coffee like aromas expressed in red wines. Research is currently limited here, but we expect to see more links between thiol levels and certain spice character.

The charts and subsequent notes presented here do not represent an endpoint, but rather an ongoing dialogue. They are by no means exhaustive and we can imagine more charts in the future linking other classes of compounds to potential descriptions. This dialogue and our understanding thereof will continue to improve, and sommeliers can become better professionals if we expanded upon both the poetry and prose of wine-tasting.