I spent much of the summer writing about people who produce some of the world's greatest wines, but the other day I realized something—I haven't written anything about the true winemakers. I'm talking about the ones who get dirty, turning grape juice into the complex beverage we all love. They're even ready to sacrifice their lives. I'm talking about yeast.
Yeasts get no respect (they really need a new publicist). Wine lovers like to credit their favorite bottle's complexity to the gravel soils of Bordeaux's Left Bank or the brilliant consulting enologist who focuses relentlessly on quality. Some even like to credit a cow horn buried in the dirt for a few months. But how often do you give a shout-out to the yeast? You think it's easy to turn sugar into alcohol? Have you ever tried to do it?
Fermentation has been mankind's favorite science experiment since the dawn of time—giving us beer, wine, bread and a lot of other delicious inventions. Until the 18th century, we didn't even know who was responsible. In 1785, Italian chemist Adamo Fabroni demonstrated that yeast initiate fermentation. But he had no idea how they did it. Only in 1857 did Louis Pasteur prove fermentation wasn't some spontaneous chemical reaction—it was a biological process. Yeast were consuming sugar, producing alcohol and reproducing—quite the wine party.
These tiny single-cell fungi—yes, a fungus made your Fontodi—are more than generators of alcohol and carbon dioxide (giving Champagne its bubbles when trapped inside the bottle during a secondary fermentation). While they're chomping on sugar, the little sweet-tooths are also breaking down other chemicals in the grapes, producing many of the aromas, flavors and textures that make wine so much more complex than spiked grape juice.
When you do hear about yeast these days, it's usually the debate between winemakers over which is better: cultured or ambient (also referred to as "native," "wild" or "indigenous") yeast. Cultured means the yeast strain was isolated in a vineyard or winery, then cultivated in a lab before being sold to winemakers, who add it to their tanks of must—they're valued because they're reliable. Ambient yeasts are already there to start the job; they cling to the skins of the grapes and hang out in the winery from past harvests. They can be more erratic, but fans of ambient yeasts believe they express terroir because they're found in a specific winery or vineyard. A New Zealand study in 2009 found 100 distinct yeast varieties at one Kumeu wine region estate and a completely different set five miles up the road in Matua.
But the great yeast spat is less clear-cut than it looks. Yeasts are opportunistic creatures. They come into wineries on people's clothes and equipment and can hang out for years, waiting for some grapes to get crushed. Fruit flies carry them from vat to vat. Most wineries are using a variety of yeasts from several sources.
The king of wine yeast is the species Saccharomyces cerevisiae, but there are others. The black sheep is dekkera (aka brettanomyces), known for chemicals that, in large quantities, can make a wine taste like the floor of a stable. Klöckera, candida, metschnikowia and hansenula are minor players.
Saccharomyces was born to be a winemaker: A Swedish team analyzing its genome has theorized that, beginning about 150 million years ago, when many of the fruits we like to eat first appeared, saccharomyces evolved the ability to keep fermenting fruit sugars at higher alcohol levels than other yeasts. Saccharomyces actually loves to produce alcohol because it gets competing yeasts dead drunk.
One of my favorite theories about yeast is that they were mankind's first domesticated microorganism. But who domesticated who? Saccharomyces evolved to feast on sugar-laden fruit; today we cultivate vines all over the world, spending endless hours caring for the grapes they'll munch on. We build beautiful wineries that are giant buffets for hungry yeast. The fungi have us right where they want us.
Considering how wonderful they are at winemaking, I'm not complaining.
Harvey Steiman — San Francisco — September 25, 2013 11:51am ET
Ned Osborn — Phillydelpia — September 25, 2013 9:27pm ET
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