If wine is made of grapes, how can we sense "hints" of other fruits and aromas?

Traditional wine is made from grapes and only from grapes. When the grapes ferment into wine, something magical happens, and chemical compounds are created that are identical to chemical compounds found in other fruits and foods. So on one level, when a reviewer is picking up a hint of berry, they might actually be identifying a berry compound. There are hundreds of these compounds, called esters. Differences in grapes, in fermentation yeasts, in barrel choices and in many other winemaking decisions can all affect the way these flavors and aromas present themselves.

Basically, esters are chemical reactions made from the grape's alcohol (sugar) and acid. The range of odors that then can release is quite phenomenal, according to the type of ester: 

• Orange
• Apple
• Plum
• Cherry
• Blackberry
• Strawberry
• Raspberry
• And so many more!

So a Chardonnay will give an apple hint, when a Grenache will leave a raspberry flavour for example.

But there are more chemical reactions going on than just the ester: 

Terpenes: Rose & Lavender

The smell of Christmas trees and desert sage are two classic examples of terpenes. In wine, they can smell anywhere from sweet and floral to resinous and herbaceous. By the way, terpenes are a highly desired trait of hops and beer making.

Lychee:GewürztraminerRose:Muscat BlancLavender:Grenache & Côtes du RhôneEucalyptus:Australian Shiraz

Thiols: Bittersweet Fruit

A thiol is an organosulfur compound that smells fruity in tiny amounts, but in larger amounts it smells like garlic and is considered a wine fault. Thiols are also a building block of earthiness.

Grapefruit:Vermentino, Sauvignon Blanc, ColombardBlack Currant:Red Bordeaux and other Cabernet Sauvignon & Merlot

Earthy Flavors

Sulphur Compounds: Rocks

Sulphur compounds may be the secret to minerality in wine. Some sulfur compounds smell fantastic, such as the chalk-like aroma in fine Chablis. Some sulphur compounds are bad, like the smell of wet wool, which is a wine fault caused by UV damage.

Chalk:Chablis & ChampagneMetallic:Young Freshly Opened Red Wine

Volatile Acidity: Balsamic & Pickle

Volatile acidity (a.k.a. acetic acid) is caused by bacteria that are present in wine making. In high doses, volatile acidity smells like acetone, but in low doses it can add great complexity and is a feature of many very fine wines.

Balsamic:Chianti & Amarone della ValpolicellaPickles:Red Burgundy

Brettanomyces: Clove & Bacon

Phenols are a group of chemical compounds that are similar to alcohols. Phenols are naturally occurring in many things including sesame seeds, peppers and even cannabis. In wine, one type of phenol is when a wild yeast called Brettanomyces can add either a lovely (clove and bacon) aroma or a very detestable (horse) aroma to wine.

Clove:Châteauneuf-du-Pape & Côtes du RhôneBacon:Paso Robles/Central Coast Syrah, Barossa Valley Shiraz

Geosmin: Earth & Mushroom

Geosmin is an organic compound from a type of bacteria. It might just be the most earthy-smelling compound out there. If you love beets, mushrooms and the smell of potting soil then Geosmin is your friend.

Soil & Mushroom:Common in Old World Wines and some new world wines Get More Wine Smarts

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Spicy Flavors

Rotundone: Peppercorn

Rotundone is a kind of terpene that is found in the essential oils of black pepper, marjoram, oregano, rosemary, thyme and basil. It gives that classic peppery aroma that you’ve probably tasted on great red wines.

Peppercorn:Syrah, Grüner Veltliner, & Cabernet SauvignonBasil:Dry RieslingPink Peppercorn:Viognier, Gewürztraminer

Lactones: Vanilla & Coconut

Lactones, and particularly gamma-Lactones are esters found in sweet and creamy smelling foods such as honey wheat bread, peaches, coconut, roasted hazelnut, butter and even cooked pork!

Vanilla & Coconut:Oak-aged red & white wineHazelnut:Aged Sparkling Wine

Thiols: Smoke & Chocolate

Thiols can taste like grapefruit pith and passion fruit, but in higher doses will smell and taste like smoky, skunk, tar and chocolate.

Coffee:Sonoma Pinot NoirChocolate:Argentine Malbec

Botrytis: Honey & Ginger

Botrytis Cinerea or ‘Noble Rot’ is a type of fungus that eats ripe fruits and vegetables. You’ve probably seen it before on a box of rotten strawberries! Despite its negative connotation with fresh fruits,it adds richness and a milieu of amazing aromas to dessert wines. There are a few compounds associated with Botrytis that you may have tasted:

• Sotolon: Honey, Fenugreek, Curry
• Furaneol: Caramel, Pineapple, Strawberry
• Phenylacetaldehyde: Rose, Cinnamon, Ginger

Marmalade:Sauternes, Tokaji
Ginger:Spätlese Riesling

It gets even more complicated than that, because in trying to describe wine, each reviewer is going to use their own language (and thus their own experiences) to paint a picture of what they taste and smell. I grew up with a sassafras tree in my backyard, so sometimes I pick up a note of sassafras, but my “sassafras” might be someone else’s “root beer” or “cola” note. I’m not going to pretend that I’m actually picking up every single chemical compound when a wine reminds me of a smell or flavor, but it certainly explains why there is some consensus about how wines taste and smell.

Do winemakers know what nuances they’re going for in production? I think yes, some winemakers are trying to coax certain specific notes out of a wine, while others may just be trying to evoke as much complexity as possible, without focusing on particular elements to emphasize.

I know that sometimes all this wine-speak can seem a bit pretentious, but I just bought a pound of coffee today that was described as having notes of “toffee and chocolate-covered pretzels,” which I picked over the one that was “crisp, with tangerine notes.” And even if you might not like talking about wine in these terms, I like to point out that not only can most people taste a difference between Coke and Pepsi, most have a preference between the two, and can even explain why.