Wine 101: Native Yeast Fermentation

An important topic of discussion regarding natural wine is “native”, “spontaneous”, or “indigenous” yeast fermentation. Perhaps you’ve heard these terms mentioned at your local wine shop, or seen them in marketing materials from a winery you like. Like most topics wine-related, it’s subject to lots of opinions and debate.

Yeasts are what ferment the sugar in grape juice into alcohol, transforming it into wine. Yeasts exist everywhere in our environment, and certain strains are indigenous to certain places. This is why San Francisco sourdough is so unique – we have our own strain of wild yeast that lives in the foggy San Francisco air, giving our bread it’s own unique flavor.

Many wineries use commercially-sold yeasts to ferment their wines. These yeasts are selectively bred or genetically altered by laboratories to enhance “favorable” flavor profiles in a wine (such as spiciness or fruit flavor), to tolerate heat extremes (cold and hot), to limit malodor in fermentations, and to produce wines with consistent flavor profiles year after year. These yeasts are also resistant to SO2, the chemical additive used in wine to prevent unfavorable microbal growth and oxidation. There are many labs out there making hundreds of yeast strains available in freeze-dried or liquid form for wineries, and each strain comes with it’s own name and marketing materials explaining it’s virtues. These commercially-sold yeasts are strong and hearty; pitch some into your grape must and they will quickly overpower any wild yeasts living in it.

Commercial yeast strains are a relatively new development in the business of winemaking. People have been making wine for thousands of years, where commercial yeasts have only existed in modern times. Grapes don’t always need help from commercial labs to turn into wine – the vineyard is full of flora that will happily do the job for free.

“Native” or “indigenous” yeast fermentations are started by wild yeasts occurring naturally on the grapes, in the winery, and in the vineyard. Pick the grapes, crush or press them, and the fermentation should just start on it’s own. These wild yeasts are usually capable of fully fermenting the wine, but at times the fermentation may seem to slow down or get “stuck”, requiring the winemaker to wait it out and see if it restarts later in the season, or to pitch a strong commercial yeast to finish the job quickly. The other issues with indigenous yeasts are that the wines may taste different from year to year, and they are more prone to producing malodor during fermentation. It’s a risk for any winemaker to choose a spontaneous fermentation over inoculating with commercial yeasts, but those who know how to do it well create (in my opinion) MUCH more interesting, complex, and soulful wines.

Some winemakers believe that there’s no such thing as a truly “native” or “indigenous” yeast fermentation, since many wineries have been using commercial yeasts for years. Those commercial yeasts get into the air and equipment in the winemaking facility, and can take up permanent residence. It’s possible that any future “spontaneous” yeast fermentation happening in that facility would be because of the commercial yeasts used in the past.

Who’s to say which yeast fermented a wine? You would have to be a scientist to figure it out. My belief is that “less is more”, and I would rather sell a wine fermented spontaneously, even if that means the fermentation started with a commercial yeast that just happens to be part of the landscape. So many new winemakers are making wine in shared “custom crush” facilities and co-ops, it’s hard to say anymore. Unless your wine came from a centuries-old chateau in France that has never seen a commercial yeast, it’s hard to say for sure whether or not your wine is truly “indigenous” or “native” yeast fermented.

It would be naïve for us to be dogmatic about this topic, insisting that we only sell “native yeast” wine, so instead we only offer wines that are fermented “spontaneously”, and never through direct inoculation with commercial yeasts. We simply feel that these wines are better – they are more interesting, delicious, and unique.