Indigenous Fermentations: Yeasts and Beasts

Vine to Wine is a column focused on winemaking and viticulture around the world. Romain Bocchio is a viticulturist and winemaker with the international wine consultancy Derenoncourt Vignerons Consultants, which is  headquartered in Bordeaux. He has degrees in winemaking and literature and collaborates as a consultant for diverse wine estates in Bordeaux, Italy, and throughout the Mediterranean basin.

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Since Louis Pasteur’s pioneering work in 1860, the science of winemaking has driven the steady improvement of wine quality. From early discoveries to revolutions, from understanding the role of yeast in fermentation to mastering stabilization, the science of oenology has displaced the empirical traditions of production.

Among respected winemakers, many seek to honor their terroir’s uniqueness and contrast two distinct approaches to vinification. The greatest wines remain the benchmark. These are wines of place – those that more than not convey with precision the distinctive character of their origin, offering tasters not only superior flavor but also a uniquely emotional dimension.

The most respected winemakers, fiercely determined to honor the individuality and uniqueness of their terroir, usually take one of two approaches to vinification. The first embraces modern scientific control of fermentation, using commercial yeasts that ensure precision but are often criticized for simplifying or standardizing taste. The second relies on faith in nature, allowing fermentations to proceed with the indigenous yeasts living on the grapes themselves. Advocates of the latter believe that nature’s own microbiological wisdom best reveals the true superiority of a spontaneous, less interventionist approach.

Would the purest expression of terroir be better revealed by native microorganisms? The answer seems obvious – yet in practice, commercial yeasts dominate. They offer clean fermentations, limit microbial deviations and reduce the risk of flaws.

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But what is the reality? Beyond the passionate debates dividing these two camps, experience provides a pragmatic analysis of the advantages and limitations of both practices. Rather than opposing one to the other, the subject demands nuance.

Alcoholic fermentation is carried out by yeasts, chiefly Saccharomyces cerevisiae, which is naturally present on grape skins. Like a personal biotope, every harvest carries its own complex population of microorganisms – a microbial identity card unique to each site and season. The quality of this microbiome reflects the grower’s discipline: soil care, pesticide use, and climate all shape the diversity of microbial populations.

Beneficial and harmful yeasts, desirable and dangerous bacteria, coexist in fragile balance, competing for sugars, acids, and other elements transformed during fermentation. These organisms succeed one another in a delicate relay, turning simple juice into subtle nectar.

The success of fermentation is a biochemical feat, both complex and delicate. Yeast survival depends on nutrition, temperature, acidity, oxygen levels and above all, rising alcohol concentration.

Commercial yeasts are identified in laboratories, selected for their varied traits, and sold to winemakers like a catalogue of fragrances: fresh or intense fruit aromas, primary or secondary notes, thiols or esters, higher or lower volatile acidity, resistance to SO₂, tolerance to alcohol, and more. The results speak for themselves. Fermentations are clean and direct; promises kept. Wines emerge precise and reliable – expressive of region, grape and soil, yet safeguarded against off-flavors. Their impact is most evident in simpler wines and is especially strategic in whites, while the finest grapes often transcend the imprint of any selected strain.

Indigenous fermentation, by contrast, is possible – and can succeed brilliantly – but demands rigor and control. Native yeasts are more fragile and less resistant to difficult conditions, yet when musts are balanced and fermentable, they can deliver perfect fermentations. This requires high-quality grapes, neither overripe nor damaged. Slow, natural fermentations offer advantages, allowing more time to adjust extraction and often producing secondary compounds such as volatile acidity—elements that, within limits, may enhance aromatic complexity.

But spontaneous fermentations carry risk. Without careful preparation, poor yeast multiplication can lead to stuck fermentations, exposing wines to spoilage organisms such as Brettanomyces or undesirable bacteria. Grapes with the highest potential alcohol are the hardest to ferment, and winemakers sometimes must introduce stronger commercial strains mid-process to finish the job. The list of hazards is long – making success all the more rewarding, and explaining why many prefer the safety of commercial yeasts.

Still, there is unmatched satisfaction in transforming a year’s vineyard work through a natural process. Vinification becomes not just a physico-chemical act but the completion of a work begun with the first cuts of pruning.

A refined path has emerged: selecting indigenous yeasts from a vineyard or estate, multiplying them in a lab and deploying the most effective strains. Traits such as alcohol tolerance, acidity production and aromatic potential guide this microbiological selection. Today, winemakers can culture their own yeasts to guarantee both authenticity and successful fermentation – though the investment is considerable.

This approach marries scientific control with microbial identity, ensuring technical precision without renouncing the idea that terroir’s purest expression depends on the living organisms it fosters. How could one not support such a quest? It is both scientifically rigorous and philosophically appealing, especially as research increasingly highlights the role of microorganisms in shaping aroma and local specificity.

This principle underlies “natural” and “biodynamic” thought but extends further. Never before have societies studied with such fascination the roles and synergies of living organisms – the microscopic and the infinitesimal, across science, medicine, agronomy and ecology. This pursuit of purity and truth is also a return to a more sincere, intimate, sensory experience.

Paradoxically, though, letting nature act requires even greater technical mastery. Too many flawed wines still hide behind the supposed superiority of “natural” winemaking. What a journey from Pasteur’s time, when science first illuminated these mysteries, to today, when some prefer to deny its progress.

Given the level of scientific and technical mastery available to us today, we have a responsibility to harness this legacy in the service of crafting the great wines of our time.

These wines must be, all at once, distinctive, rooted in identity, natural and precise. Scientific knowledge and its technical applications should not be viewed as a modern affront to nature, but rather as a powerful tool to help us better understand its most authentic expression.

To produce wines that move us – wines that faithfully reflect their terroir while resonating with emotion – the goal must remain the successful mastery of native yeast fermentations. By balancing science and nature, by guiding the living forces of fermentation without suppressing them, wine reveals its purest truth.

– Romain Bocchio