Acetic, lactic and butyric acid: where each one comes from at the palenque
There are three acids worth knowing in mezcal: acetic, lactic and butyric. All three are born in fermentation, when native yeasts and bacteria share the vat. In small amounts the first two add freshness and complexity; butyric acid, on the other hand, is almost always a sign of a flaw.
The three acids at a glance
| Acid | Produced by | Smells like | Flaw? |
|---|---|---|---|
| Acetic | Acetic and heterofermentative lactic bacteria; also agave roasting | Vinegar | Only in excess |
| Lactic | Lactic acid bacteria (Lactiplantibacillus, Leuconostoc) | Yogurt, cream, fresh cheese | Only in excess |
| Butyric | Clostridium bacteria, without oxygen | Rancid butter, vomit | Almost always |
Acetic acid
Mezcal's main acid. Part of it forms during roasting and part during fermentation. Artisanal mezcals from Oaxaca have shown 75 to 409 mg per 100 mL of anhydrous alcohol (Sánchez-Fernández et al., 2025). During distillation it concentrates in the tails (Vera Guzmán et al., 2009).
Lactic acid
Made by lactic acid bacteria living alongside yeasts in the vats. A study of four Oaxacan palenques found genera such as Lactiplantibacillus, Leuconostoc and Levilactobacillus. By producing acids, they lower the pH and stabilize fermentation (López-Sánchez et al., 2026).
In balance it adds creaminess and soft dairy notes. In excess, the mezcal smells like sour cream.
Butyric acid
It shows up when Clostridium bacteria grow without oxygen, for example when mash or water sits in the vat too long. It smells like rancid butter. The trade publication Mezcalistas lists it, along with caproic acid (goaty) and acetone (nail polish remover), as a sanitation or handling fault, not "character" (Spear, 2025).
How to spot them when tasting
- Pour the mezcal into a copita or veladora and let it breathe for a minute.
- Smell with your mouth slightly open, without diving in.
- Citrus freshness and fruit: acids in balance.
- Obvious vinegar or nail polish: too much acetic acid or a poor cut.
- Rancid butter or goat: a fermentation fault.
How it applies to ZUNTE
ZUNTE ferments for 12 to 15 days in wooden vats with crystal-clear water and is double-distilled in a copper still over 35 hours. Master distiller (maestro mezcalero) Juventino Cruz aims for citrus, herbal and light-smoke notes: acids should add freshness without taking over.
FAQ
Which acid is a flaw in mezcal?
Butyric acid almost always is: it smells of rancid butter and comes from bacteria that grow without oxygen.
Is a slight dairy note normal?
Yes, at low intensity. It comes from lactic acid bacteria in fermentation.
Where does a vinegar smell come from?
From excess acetic acid, due to long fermentations or a poor tails cut.
