The three workshops behind the smell of your wine

Read a wine shop's note on a Cabernet: bell pepper, blackcurrant, vanilla, forest floor. Yet nobody slipped a bell pepper into the tank or a vanilla pod into the barrel. Wine is nothing but fermented grapes, and it makes these smells all by itself: first at the winery, in three workshops that follow one another (the vineyard, the fermentation tank and maturation), then at your place, in your cellar, with time. Knowing who did the work helps you understand what you're smelling, and why a wine changes as it ages.

Professionals talk about primary, secondary and tertiary aromas, depending on the stage at which they appear. Apart from two nuances we'll get to along the way, it's the same breakdown.

First workshop: the vineyard

Some smells are already in the grape when it's picked. They come from the variety and from the way it ripened. The green bell pepper of some Cabernets is a good example: it comes from a molecule present in the berry, which decreases as the grape ripens. Picked too early, a Cabernet keeps more of it.

Another example: the black pepper of some Syrahs. In Adelaide, Claudia Wood and her colleagues at the Australian Wine Research Institute identified the molecule responsible and found it already in the grape: Syrah's pepper is made in the vineyard. Their study held a surprise. About one taster in five on their panel couldn't smell the molecule at all, even at the highest dose tested. So when five friends around a peppery Syrah rave about the pepper, one of them may be faking it.

Second workshop: the fermentation tank

Crush a Cabernet grape: part of the blackcurrant you'll find in its wine can't be smelled yet. It's there, but locked away, attached to another molecule that makes it odorless. This mechanism was uncovered in Bordeaux, by Denis Dubourdieu's team, first in Sauvignon Blanc, whose grapefruit hides the same way. During fermentation, the yeast cuts the link and releases the smell. The molecule comes from the grape; fermentation wakes it up. That's the first nuance: blackcurrant remains a vineyard smell that the yeast merely unlocks, and professionals class it among primary aromas.

Fermentation also makes smells of its own that were never in the grape, and these turn up in every wine, Cabernet included. As they turn sugar into alcohol, yeasts produce notes of brioche and fresh bread, and sometimes banana or fruity candy, very pronounced in young "primeur" wines like Beaujolais Nouveau. One famous strain, identified by a mere serial number, 71B, is known for exactly that. The banana and candy notes are fragile and often fade within the first year in bottle.

After the yeasts, bacteria can take over, during a second fermentation that makes the wine less acidic. They're mostly responsible for the buttery smell of some wines.

Third workshop: maturation

Between the end of fermentation and bottling, the winemaker lets the wine mature, in tank or in barrel. The French call this stage élevage, literally "raising." Back to our Cabernet: if it matures in oak barrels, it picks up vanilla and coconut, and the toasting of the wood by the cooper adds toasty, smoky notes. A new barrel marks the wine more: the wood wears out with each use, and after a few years the barrel is little more than a container.

Then, your cellar

Once the wine is bottled, the workshops close, but the wine keeps changing, sometimes for decades. No more intervention, no more yeast, no more wood: the wine's molecules slowly react with one another. The fermentation smells fade, and others appear that a young wine doesn't show yet: leather, forest floor, truffle.

In Bordeaux, researchers at the Institute of Vine and Wine Science count forest floor and truffle among the markers of the bouquet of aged red Bordeaux, where Cabernet is one of the grapes. That's the second nuance: professionals group together, as tertiary aromas, what maturation brings at the winery and what the years bring in your cellar.

Smell your glass and sort what you find. Blackcurrant, bell pepper and black pepper come from the grape, even when fermentation woke them up. Brioche, banana, candy and butter were born during fermentation, from the work of yeasts and bacteria. Vanilla and toast come from barrel maturation. Leather, forest floor and truffle: that's the years. The sorting isn't always clean: everyone is working on the same wine.