Cara Morrison, Chardonnay winemaker at Sonoma-Cutrer in California’s Russian River Valley, believes in the power of yeast.
“I consider yeast as winemakers, since yeast converts the sugar of grape juice into alcohol,” says Morrison. “Without yeast, we only have really yummy grape juice.”
For winemakers, yeast functions like a key that unlocks a different dimension of the grape juice. During the fermentation process, yeast releases aroma and flavor compounds bound to the sugars in the juice. Those sugars, along with other chemical elements like acid and nutrient levels, plus fermentation process, aging, variety and regional characteristics, all shape the end product: the wine you’ll drink at a dinner table somewhere.
Like wines, yeasts vary and satisfy different needs. Cultivated yeast is grown for specific grape juices, and there are many to choose from. Often, cultivated yeasts are wild yeasts that are collected in the vineyard, multiplied and then packaged, says Nicholas Ducos, owner and winemaker at Mural City Cellars in Philadelphia.
“For example, for our Carbonic Chambourcin, we chose yeast sourced and cultivated in the Beaujolais region of France,” says Ducos. “They do this by collecting yeast samples off the plants and bringing them back to the lab to create a yeast culture, allowing them to reproduce. They are then freeze-dried and sent to us in Philadelphia.”
Cultivated yeasts tend to be more neutral, says Morrison, which is useful when you want the natural terroir to come through. “Some yeasts are more varietal-specific, such as yeast that can enhance aroma precursors in Sauvignon Blanc,” she says.
Cultivated yeasts also increase odds that the fermentation will successfully complete and the appropriate amounts of sugar will convert into alcohol.
“Cultivated yeast brings winemakers peace of mind,” Morrison says. “All in all, cultivated yeast is predictable, which is very important for a winery like Sonoma-Cutrer, which ferments Chardonnay in barrels, and each barrel can be described as its own individual fermentation vessel. [We] can have thousands of little fermentations going on during the month of September.”
On the other hand, wild yeast is less predictable. Morrison compares it to wild versus domesticated animals.
“In the right circumstances, they can be very interesting and unique,” says Morrison. “Wild yeast needs a lot of attention and possibly winemaker intervention to ensure sugar completion.”
Wild yeast may ferment too fast or slow or stop fermenting with too much or little sugar still in the wine. They can create funky aromas or flavors, like vinegar or burnt rubber, in finished wines. Because of these potentially volatile variables, heeding the call of the wild is usually more suited for small-batch winemaking.
“The real difference between wild and cultivated yeast in winemaking is the ability to control the point that the fermentation process begins,” says Ducos. “If you, as a winemaker, are pitching yeast, you have the ability to choose a strain and control fermentation, creating certain flavors and aromatics. With wild yeast, it’s a gamble because you don’t know which of thousands could take over the fermentation.”