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  • 29 September 2021
  • Wine 101 Guides

Natural Yeast Fermentation in Wine

Fermentation: Yeast + glucose (sugar “food”) = ethanol (alcohol) and CO2 

Seems like a simple enough equation, right? 

Not quite. It wasn’t until the mid 1800s that human beings discovered this process. Even today, now that we know the scientific process behind the production of alcohol, there remains a mystical air about it. When winemakers choose to let their wine ferment naturally, as opposed to adding lab-cultured yeasts, this mystical air is heightened. No two natural fermentations are ever the same, and the flavours that arise from the yeasts are perhaps just as significant as the grape variety or the soil on which the vines are grown. 

But what does it all mean?

Illustration by Samme Snow

The History — Sacred yet Dangerous

In ancient times, wine was seen as a mystical, sacred liquid — perhaps because fermentation was not yet understood. Dionysus was the Ancient Greek God of fruitfulness, vegetation, wine and ecstasy. Although they drank wine diluted with water, the Ancient Greeks heralded wine. They held drinking symposiums where they would perform poetry, not entirely unlike an ancient alternative to today’s music festivals. 

The somewhat barbaric Scythians—nomads—drank their wine ‘unadulterated’ (i.e. not mixed with water), from the skulls of the conquered. They considered the liquid of such importance that they swore their oaths by drinking human blood mixed with wine. The prize for people who had slain their enemies was wine. However, it was also feared; the Romans had complex relationships with wine, both celebrating it, but also banning it from time to time. Under Romulus, women were prohibited from drinking wine in order to prevent adultery (Roman society was extremely patriarchal). While it was considered to have health benefits, it was also considered to have the potential to drive one to madness. Alas: a complicated relationship. 

Throughout the Middle Ages, the importance of wine spread throughout Europe, largely due to the power of the Church, which needed wine for sacramental purposes. It was also considered the most luxurious beverage, and thus was present throughout the royal and noble circles. 

Yet still, nobody could explain how grape juice became wine.

Natural fermentation at Jaimee Motley. Photo by Leigh-Ann Beverley

The Discovery of Fermentation

Between the 1600s and the 1800s, many scientists worked on microbiology, trying to comprehend the relationships between yeast and chemical reactions. Antonie Philips van Leeuwenhoek, a Dutch scientist, noted yeast under an advanced self-made microscope for the first time. However, he did not identify their role, and he didn’t identify them as fungi. French physicist Cagniard de La Tour noticed the growth of these globules in beer, and so was able to conclude that during fermentation, yeast multiplied. Both scientists had noticed gas bubbles being produced, but neither identified the gas as carbon dioxide. Next, three other scientists, Schwann, Kutzing and Erxleben, independently concluded that yeast were living organisms. This discovery changed how fermentation was understood, and soon after, the famous Louis Pasteur finally came to a conclusion in 1857. 

Louis Pasteur’s breakthrough

Louis Pasteur was the first to show that these living organisms were responsible for the transformation of glucose into ethanol, hence concluding that yeast are responsible for alcoholic fermentation. He also noted that this takes place in the absence of oxygen, which he named ‘respiration without air.’ He also discovered that lactic acid fermentation takes place due to bacteria, not yeast. So, Louis hit the jackpot, and fermentation was understood for the first time in millennia. 

Yeasts: Wild or Cultured?

Once upon a time, we didn’t have the laboratories that exist today for the purpose of isolating or breeding yeast strains for fermentation. It wasn’t until almost a century after Pasteur’s breakthrough that people began to isolate yeasts in laboratories. Before this, all wine was produced via natural fermentation, thanks to wild yeasts. These wild yeasts are found in vineyards, as well as in the winery environment (even in your house and neighbourhood).  Yeasts are everywhere. 

“Commercial” or “cultured” yeasts first appeared in the 1950s and became very popular in the decades to follow. Scientists took existing yeast species from nature and propagated them in laboratories, isolating those that had desirable characteristics. This could be anything from carrying out fast fermentations, to having a good tolerance to high alcohol levels, and even to producing specific flavours in wine, such as citrus, floral or earthy aromas. 

Almost all of them are from the Saccharomyces cerevisiae species (the same species that is used in bread making, and inoculated beer and cider making).

They provided stability and reliability, and therefore they boomed in popularity. Winemakers who had experienced stuck fermentations (and subsequent bacterial issues) suddenly had a solution. In the space of just two decades, natural fermentation went from being the norm, to something far less common.

Saccharomyces cerevisiae

However, although they provide a reliable fermentation environment, using cultured yeasts takes some of the mystery out of the winemaking process. Wild yeast fermentation chemistry is immensely complex, and there are several genera of yeast at play. In commercial yeast fermentation (using cultivated yeasts that come in packets), however, you know exactly which yeasts will take over the fermentation (usually one species of saccharomyces cerevisiae), and other yeasts get 'less say' in the matter. The natural yeasts present in the fruit and in the cellar are not really given the opportunity to express themselves if you add one certain strain straightaway.

Imagine a great bar or festival where people are partying together. This is kind of like a wild yeast party. Then, imagine a futuristic bar where you find the same person cloned thousands of times. That is a commercial yeast fermentation: the other people might have been lining up at the door, but they weren’t allowed into the party. Only the clone is.

Which yeast?

This is where it gets a bit complicated. In natural fermentation, it’s also saccharomyces cerevisiae that will be the yeast to finish the fermentation, as it multiplies at a much faster rate than other yeasts, and it’s found almost everywhere.

Other yeast genera also tend to be less tolerant of alcohol, hence eventually slowing down and no longer reproducing, letting saccharomyces cerevisiae take the win (saccharomyces cerevisiae is the Usain Bolt in this scenario). However, the other yeasts are still very much active in the early stages, each contributing their own elements to the final race. 

The yeasts other than saccharomyces cerevisiae which also appear most commonly in vineyards, and in wild fermentations, are Kloeckera, Candida, Pichia, Brettanomyces, Torulaspora delbrucecki, Cryptococcus, Rhodotorula and Zygosaccharomyces… a mouthful, we know. 

East yeast ‘family’ is different, and each has the capacity to contribute different aromas and personality traits to wine. 

Cryptococcus: one 'natural yeast'

Candida: another

The Philosophy of Natural Fermentation

Angiolino Maule of the winery La Biancara in Gambellara, and founder of natural wine research group VinNatur, says, 

“Local yeasts are part of the biodiversity and are a unique heritage that should be nurtured. Natural fermentation allows us to arrive at the objective — that is, to transmit typicity and authenticity in the wine.”

Jean-Pierre Frick, from Alsace, has always been cynical of adding yeasts, or any additive, for that matter. He explains his reasoning:

“Oenologists are known as Wein-Artz in Alsace, which translates as wine doctors. Let’s compare it to this. If you have a small niggle, and you go to a doctor and they write a prescription, and there’s nothing on the prescription, people will say they are a bad doctor…” 

Angiolino Maule

Jean-Pierre Frick

Sylvain Dittière

A Matter of Taste & Natural Yeasts as terroir translators 

Some wineries may add ten or more lab-cultured yeast strains specifically to achieve a certain taste profile. By doing so, however, the wine becomes more influenced by human decisions, and thus perhaps expresses its ‘sense of place’ less. Sylvain Dittière, in Saumur, says,

“Natural yeasts give the wines their taste. If you add yeast, then the wines end up tasting the same. It’s the diversity of the yeast and bacteria population that gives the wine its character.”

Guy Breton, winemaker in Beaujolais, works with only one grape variety — Gamay — and the same winemaking protocol across all of his Cru wines. The soil types vary greatly from parcel to parcel, and the taste of the resulting wines vary greatly, also. He is convinced that it is the natural yeasts found in each plot that express these differences, as opposed to the soils directly imparting flavours. He says, 

"By working with natural yeasts, your vineyards - even if they're just 500m away from each other - will create wines with totally different tastes."

He learnt this from Jules Chauvet, wine merchant and biochemist. Jules explained that in order to show true terroir, fermentation should happen spontaneously from natural yeasts, as the expression of terroir should also reflect the living side of the soil; the symbiotic relationship between the soil and its microflora.  To achieve a healthy natural fermentation, he emphasised that these aforementioned sprays must not be used. Instead, one must return to the age-old practice of ploughing the vineyards. He was also against judicious use of sulfites, as the use of too much would inhibit the work of the natural yeasts present on the berries and in the winery, thus stopping them from reflecting the details of the terroir.

Interestingly, Angiolino Maule adds that he thinks the ‘other’ species of yeasts (the ones with the other complicated names above, not saccharomyces cerevisiae) are the ones that play a role in expressing vintage variation. He says,

“Apiculate yeasts [apiculate refers to the shape, which is leaf-like, whereas saccharomyces cerevisiae yeasts are ovoid in shape] change a lot depending on the vintage, based on humidity and summer temperatures, and depending on the vineyard. They are responsible for the aromatic expression of the single vintage, and the single vineyard. They carry out the first part of the fermentation, then at about five degrees of alcohol they are replaced by saccharomyces yeasts, which are more resistant to alcohol. The saccharomyces yeasts are usually not very present in the skin of the grapes, but are rather considered "cellar yeasts", therefore more constant over the years.”

Anne-Sophie Dubois

Natural, but Scientific

While learning with Jules Chauvet in the Beaujolais, Guy Breton and the other members of the ‘gang of four’ (the group of organic and naturally-focused Beaujolais pioneers) learnt how to study wine under a microscope, and how to identify yeasts. This means they were able to err on the side of caution and avoid any unwanted yeasts or bacteria taking over. Today, this knowledge has also been passed down to many others, and young natural winemakers are also working with microscopes. 

Anne-Sophie Dubois, of Fleurie, explains, 

“When you work with natural yeasts, you need to smell the wine often - to make sure it smells healthy. Then, I also look at the juice under a microscope to see what’s happening on a microbial level – the different populations of bacteria and yeast. We owe a lot to Jules Chauvet, Jacques Néauport and Marcel Lapierre. They’ve left so much knowledge for us… a “connaissance.” 

Anne-Sophie's Gamay juice under a microscope: the round ones are probably saccharomyces whereas the long ones are another species of native yeast: Schizosaccharomyces

This works as a form of reassurance, and winemakers are able to detect if something looks to be going awry, and react accordingly. Anne-Sophie says, 

“It’s not just about organic grapes; it’s about avoiding additions, and listening to your grapes. You have to have a passion for viticulture and vinification. Yes, you’re a farmer, but you also need to pay attention to the wine you are making. I don’t accept faults. This way of making wine - it’s not about doing nothing…

Pied de Cuves

One way to ferment naturally, while also being careful, is to use a pied de cuve. This is very similar to using a sourdough starter. Before harvest, winemakers will collect some grapes from their vineyard and start a micro-fermentation. This means they can check that the fermentation is going well, and that any unwanted yeast or bacteria haven’t taken over. They then use this to pour into the newly harvested juice/grapes to kick-start that fermentation. Some winemakers use just one starter for all tanks. However, some winemakers argue that if you do this, you diminish individual vineyard expressions. Another option is to do the pied de cuve vineyard-by-vineyard — this approach allows winemakers to hone in on the individual microbiology of each site.

Tara Gomez, an Indigenous Californian, member of the Santa Ynez Band of the Chumash Tribe, and Mireia Taribó, from Catalunya in northeastern Spain, founded their winery Camins 2 Dreams in Santa Barbara. They are both scientists by training, but have decided to pursue the natural winemaking route. They create pied de cuves for each of their vineyards to explore the unique terroir differentiation across the plots they work with. Tara says, 

“Our goal is to showcase each of the vineyard sites through the natural yeasts that live there. So, we start a pied de cuve from each vineyard.”

Mireia & Tara

Mireia adds,

“Because we both have a background in chemistry, it means that we really understand the chemistry of winemaking. That means we can make natural wine with the knowledge of what might happen, and therefore what you can and can’t do. We make all of our decisions – from when to pick and what to do in the cellar – with those facts in our minds. It’s not just a case of just I’m gonna make natural wine – you have to understand the wine and the process. It makes it a little bit easier for us to have that knowledge, and perhaps a little less risky, although you do always have a risk with natural wine.”

As we talk, the smiles in their eyes tell us that the risk is worth it. Each yeast found in a natural fermentation exists for a reason: it has found an area in which it thrives. As such, you’ll find different yeast strains living in different areas according to which environment suits them best—not all that dissimilar from animals living in different habitats. And for these winemakers, capturing the essence of the places with which they work—naturally—is part of their raison d’être.

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