The Importance of Knowing Your Yeast


The first type of yeast that I was introduced to was bakers’ yeast, aka saccharomyces cerevisiae.

I would drag my teenage self out of bed every Thursday morning at 6am to head down to the bakehouse and knead 200 2lb loaves. I also used to volunteer on Wednesday evenings to prepare a big vat of yeast and warm water. By morning, the yeast was ready to go. I loved that funky smell and the way it had miraculously frothed up.

Yeast is also one of the buzzwords of natural wine. The debate between ambient vs cultured yeasts is one of the key sticky points between the two camps.

Yet very rarely do we find out exactly which yeasts are being used. For the layman who is curious about natural fermentation, the answer “it’s precipitated by yeasts which are found naturally on the skins and in the air” seems to suffice. The thing is, have we ever actually stopped to ask exactly what is doing the work?

Most natural wine producers are so small they don’t have the means to do extensive lab-testing. If the yeasts do their job and the alcoholic fermentation happens correctly, the winemaker seems content enough.


Open-air Fermentation Tanks

Mezcal, the agave-based spirit that is too often thought of as tequila’s little brother, is “naturally” fermented in large oak vats, in the open air, before distillation. For the basis of this comparison, I’m only refering to small-scale, traditional mezcal where the addition of any kind of “fermentation accelerator” is not permitted.

Despite the elevated temperatures in Mexico, it takes approximately four to ten days for the fermentation in Oaxaca. Very definitely comparable with natural wine-making.


Hipocrates, the President of the CRM (previously known as COMERCAM) gave a fascinating masterclass at the La Perla bar in Paris in April 2014. Four months on and I’m still thinking about it. He shared some pioneering research that he had conducted on the presence of yeasts at the different stages of fermentation in different palenque.

mezcalHe identified sixteen different strains of naturally-occuring, airborne yeasts. The diagram above shows the extent of the presence of these yeasts in different producers within the Yautepec region at three different moments during the fermentation. Take the Palenque ZA for example (top left), at the beginning they have equal amounts of 1, 2, 4 and 11. Half way through, there’s just 2, 3 and 4. Right at the end, there’s a lot of 2. Conversely, Palenque VB (bottom middle) only has two strains (1 and 5) which both appear late in the process and in equal measure.

Why does this matter? Well, we know that the yeasts play a key part in defining the flavour profile of the final liquid. If we know which yeasts are present, we have a scientific explanation for why certain mezcals taste alike and why others don’t.

I do not know of any similar studies for winemaking.* The most recent study I’ve seen in a similar field coming out of Europe was from INRA in Montpellier (here) confirming that wasps are a vector for the natural spread of yeast within a vineyard. But, seriously, did we not know that already?!

I suppose the crux of the matter is to ask why natural winemakers are happy to maintain a veil of mystery? I would be prepared to argue that natural wine has long been defining itself by what it is not. A rather reactionary, anti-establishment approach, if you like. I am certainly not advocating any kind of manipulation in winemaking but wouldn’t it be nice, just sometimes, to know what nature is doing instead?


Gracias to Hipocrates and the CRM and a shout out to a mezcal fan so notorious that he just goes by the name Pancho. 🙂

For further reading, I recommend this article on “yeast communities in a natural tequila fermentation” by Marc-André Lachance at the Herradura distillery… but if you want to get any further than the abstract, it’ll set you back 40€.

* I acknowledge that we test barrels for the presence of “bad yeasts” such as bretts before resell, but this is for a commercial interest rather than furthering our knowledge of natural winemaking.