Wooden-vat fermentation: temperature, native yeasts and timing
Fermentation is the stage where roasted agave juice becomes alcohol, and in artisanal mezcal it happens naturally: no commercial yeast, in open wooden vats. It takes several days and builds much of the aroma. That's why two palenques using the same agave can make very different mezcals.
What happens inside the vat?
After the roasted agave is crushed, the fibers and juice (the mash) go into vats with water. Yeasts and bacteria living in the air, the wood and the agave itself start eating the sugars. Yeasts make alcohol and aromas; lactic acid bacteria make acids that lower the pH and protect the ferment.
Data from real fermentations in Oaxaca
A 2023 study followed fermentation at four palenques in Oaxaca (Vázquez-López et al., Beverages):
| Variable | Observed value |
|---|---|
| Vessel | Wooden vats of 2,000–2,500 L (three palenques); plastic tanks at one |
| Duration | 5 to 7 days, depending on weather |
| Temperature | 26–28 °C (79–82 °F) |
| pH | Drops from 4.8 to 4.3 |
| Yeasts | 8 genera: Saccharomyces, Pichia, Torulaspora, Candida, Clavispora, Meyerozyma, Yarrowia and Metarhizium |
The same study found that palenques using an earthen oven and a traditional tahona had more yeast diversity than the one using mechanical equipment. The whole process, not just the vat, shapes the flavor.
Why wood?
- It harbors microorganisms in its pores, which help kick-start the next fermentation naturally.
- It insulates, softening temperature swings during the day.
- It's tradition in Oaxaca's Central Valleys, alongside stone and rawhide in other regions.
How long should it take?
It depends on the weather, the agave and the palenque. In hot weather fermentation runs faster; in cold weather, slower. What matters is distilling when fermentation is done: if the mash sits too long, bacteria that cause vinegar notes or flaws take over.
How it applies to ZUNTE
At ZUNTE's palenque in San Luis del Río, espadín agave, roasted for 4 days and crushed with a tahona, ferments for 12 to 15 days in wooden vats with crystal-clear water and the site's native yeasts. It's a traditional way of working, today led by master distiller (maestro mezcalero) Juventino Cruz, and one reason for its citrus, herbal profile.
FAQ
Does artisanal mezcal use commercial yeast?
Not usually. It ferments with native yeasts and bacteria from the air, the wood and the agave.
How long does mezcal take to ferment?
In a study of four Oaxacan palenques, 5 to 7 days depending on the weather.
At what temperature does it ferment?
In that study, 26–28 °C (79–82 °F).
Why wooden vats?
They harbor helpful microorganisms, soften temperature swings and are the tradition in the Central Valleys.
