Indigenous Yeasts: When Fermentation Tells the Story of Terroir

Imagine a painting painted identically by two different painters, on the same canvas, with the same colors—but each with their own gestures, their own rhythm, their own sensitivity. The result would inevitably be different. This is exactly what happens with yeasts in wine.

When a natural winegrower harvests their grapes, they add nothing to trigger fermentation. The sugars in the grapes will ferment into alcohol naturally, thanks to indigenous yeasts—the millions of single-celled microorganisms that naturally colonize the skins of the berries, the surfaces of the winery, and the ambient air. Each plot, each cellar, each vintage has its own unique yeast population. And this uniqueness is reflected in the glass.

What is an indigenous yeast?

Yeasts are microscopic fungi capable of converting the glucose and fructose in grapes into ethyl alcohol and CO2. This process—alcoholic fermentation—has been known since antiquity, long before its biochemistry was understood.

Indigenous yeasts, also called "wild yeasts" or "natural yeasts," are those found naturally in the vineyard and winery environment. Their diversity is staggering: dozens of different species can be found in a vineyard, including Saccharomyces cerevisiae (the most efficient yeast for completing fermentation), Hanseniaspora, Lachancea, Metschnikowia, and many others.

Each species brings its own aromas, its own fermentation speed, its own needs. Spontaneous fermentation is therefore a complex ballet where these species succeed each other, inhibit each other, and then give way to Saccharomyces to finish the work.

Indigenous yeasts vs. active dry yeasts: two philosophies

In industrial viticulture, the use of active dry yeasts (ADY) has been the norm since the 1970s. These laboratory-selected yeasts are chosen for their efficiency, resistance to alcohol and SO2, and above all, their aromatic consistency. An ADY of the "fruity Bordeaux" type will produce similar aromas in Montpellier, Bordeaux, or Melbourne. It tends to reduce the expression of local microbial diversity in favor of a more predictable fermentation profile.

For a volume producer seeking to maintain a consistent profile from year to year, it's a valuable tool. For a natural winegrower who instead aims to capture the specificity of a plot and vintage, it's exactly what they don't want.

The natural wines of Roussillon precisely claim this refusal: no added yeasts, spontaneous fermentation with indigenous yeasts. This choice involves more risks (a stuck fermentation, a slow start) but opens the door to deeply individual wines.

The winery microbiome: a unique signature

The fascinating particularity of indigenous yeasts is their geographic anchoring. The yeast populations of a winery in Maury are different from those of a winery in Collioure or Vinça. The wood of the vats, the door seals, the schist walls—the entire structure of the winery harbors its own microbial community, built over years or decades of winemaking activity.

This winery microbiome is in a way the biological memory of the place. It explains why a winemaker who takes over old cellars often observes their first spontaneous fermentations as more complex and richer than those of subsequent years: the yeasts from the previous cellar are still present, mixing with the new ones.

Recent metagenomics studies have begun to map these yeast populations across several vineyards and have confirmed what winemakers empirically observed: the composition of indigenous yeasts varies significantly from one estate to another within a radius of a few kilometers.

Roussillon, a particularly rich microbiome

The climatic conditions of Roussillon—hot, dry summers, low humidity, intense sunshine—create a particular microbial environment, different from cooler, humid regions. The low pressure of fungal diseases (botrytis, downy mildew) limits the presence of unwanted yeasts and bacteria that thrive in wet years.

The local grape varieties—Grenache Noir, Carignan, Grenache Gris, Macabeu—have co-evolved with local yeast populations for centuries. This co-evolution may contribute to the consistency of spontaneous fermentations that Roussillon winemakers observe on their traditional varieties, even without the addition of selected yeasts.

What indigenous yeasts bring to the glass

The central question remains that of taste. What do indigenous yeasts concretely bring compared to selected yeasts?

The answer is not simple, because the influence of yeasts on aromas depends on their specific composition. Non-Saccharomyces species—those that work at the beginning of fermentation—often produce atypical aromatic compounds: glycerol that adds roundness, complex esters with floral or spicy notes, fatty acids that contribute to texture.

Spontaneous fermentations generally last longer than fermentations with selected yeasts. This slow fermentation, often at low temperatures, favors the development of complex aromas—floral, spicy—that rapid high-temperature fermentations do not produce in the same way.

Wines fermented with indigenous yeasts are often described as more "alive," more "expressive of place," less predictable but more individual. Some natural wine enthusiasts describe a slight initial roughness on the palate that disappears with aeration and then reveals the wine in all its dimension.

To experience these differences concretely, the winemaker workshop at Mas Llossanes offers an introduction to comparative tasting.

FAQ

Can a fermentation with indigenous yeasts fail? Yes, it is a real risk. Fermentation can stop prematurely (stuck fermentation) if the indigenous yeasts present are not sufficiently Saccharomyces, or if temperature or hygiene conditions are not optimal. Risk management is an integral part of natural winemaking.

Can natural wines fermented with indigenous yeasts have defects? Certain compounds produced by some species of indigenous yeasts can give undesirable aromas (mousy, Brettanomyces). Grape quality and winery hygiene are key factors in minimizing these risks.

Is sulfur compatible with indigenous yeasts? A moderate dose of SO2 (sulfur) is often added to the must to inhibit less desirable bacteria and yeasts while allowing indigenous Saccharomyces to work. Natural winemakers seek to minimize or even eliminate these additions.

Can you see yeasts with the naked eye during fermentation? No, yeasts are microscopic. But you can see the effects of their work: the CO2 that makes the must bubble, the heat that rises in the vat, the foam on the surface. These visible signs are what the winemaker monitors to manage their fermentation.

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Sources: Les Vins Naturels, Wikipedia — Yeast, Journal of Applied Microbiology — wine microbiology