Feral Yeast or Wild Yeast? And Why?

Wild yeast is a constant subject of debate in the wine business, even though wine's origins started with indigenous yeasts finding their way to grapes and fermenting them. We didn't even begin to identify or understand yeast until the late 1800s. In the California wine business, wild yeast fermentation seems to have gone out of style somewhere between the late 1970s and mid-1980s.

The debate often is: wild or feral? And does it matter?

We've never inoculated at Foursight's Boonville winery, just trusting past experience that our fermentations are vigorous and complete, and using yeast that are present in our vineyard and winery. But two years ago our curiosity finally became too much and we sent our first sample of an active fermentation off to ETS Labs -- one of the wine industry's largest laboratories. (A second sample from a different variety, at a different stage of fermentation, was submitted the next year.)

The test is called DNA Yeast Fingerprinting. The process, simplified greatly, is: they plate the wine sample, select a random number of colonies, then extract DNA and try to identify the dominant strain.

In our sample, they found that none of the strains were in their database of commercial yeasts. Focusing on the most populous and therefore vigorous strain, the report says: "..If it is a native strain, it is well suited for the conditions found in this fermentation, providing a competitive advantage over the other strains present in the fermentation." And the same strains found during active fermentation of our Pinot Noir were also found pre-fermentation in the next year's Sauvignon Blanc.

Several articles have been published in the past few years, debating whether or not you can have a true "wild" yeast fermentation, pointing out what those of us in the business see as obvious: if you make wine in a facility where you've ever inoculated before, or if you're next door to a facility that does, you'll simply get their commercial yeast in your vats. (In one of these studies, they added 40 ppm of sulfur at the crushpad, which by itself will kill a ton of native yeasts and bacteria, thereby kind of assuring the results.)

Studies have also indicated that different yeast combinations are often found in fermentations with grapes from different vineyards, showing that there is diversity by site. (A few articles follow at the bottom, in case you want to read further.)

This is what we know about our fermentations at Foursight:
  • One of the wine industry's largest laboratories can't match our yeast strains to anything in their commercial catalog
  • One of the DNA tests was conducted pre-fermentation, right after we pressed our Sauvignon Blanc, indicating that a number of the strains present should have come in on the grapes, from the vineyard
  • We have never inoculated for primary OR malolactic fermentations (yes, all our wines go through completely native ML fermentations, even the whites)
  • We use only estate-grown fruit, grown on the same site as our winery (no outside fruit has been on our property)
  • We started making wine in a brand new building (no prior winemaking or, well, anything) 
  • Every used piece of equipment or barrel that entered this building was sterilized via ozone machine before entering
All this would indicate that nature found its own way to provide us with the yeasts and bacterias from our site to complete our fermentations. And the beautiful thing: the makeup of those yeasts and bacterias will be slightly different every year, due to variations in the vineyard and winery (weather, etc.), making our wines truly represent our site each and vintage -- without intervention or addition.

There's a reason the French have the phrase goût de terroir.

Not-too-geeky articles to read:

Excellent, more geeky read:


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