Vegan Fermentation Basics: Yeast, Lacto, and Mycelium

Fermentation is metabolism in a jar. Microbes eat sugars and excrete acids, alcohols, gases, and flavours that transform food entirely. For plant-based cooks, it is a quiet superpower — the difference between plants that taste of themselves and plants that taste of something else.

The Three Variables That Govern Every Ferment

Every ferment is a controlled fight between wanted and unwanted microbes.

• The microbe. Yeast, lactic acid bacteria, mould, or acetic acid bacteria. Each produces different byproducts.

• The substrate. The food being fermented. Sugars, starches, and proteins all behave differently.

• The environment. Temperature, salt concentration, oxygen availability, time. Shift any one and the dominant microbe changes.

Most home fermentations do not require a starter culture. Wild microbes already live on vegetable skins, flour, and grains. The cook's job is not to introduce microbes — it is to shape conditions so the wanted ones win.

The chef doesn't ferment. The chef creates the conditions where fermentation happens right.

The Four Types Worth Knowing

Four categories cover almost every plant-based ferment.

1. Yeast fermentation. Sourdough, pizza dough, ginger bug, tepache. Saccharomyces cerevisiae and wild yeasts convert sugars into ethanol and CO₂. Best at 24–28°C. The CO₂ leavens bread; alcohol is a byproduct.

2. Lacto-fermentation. Kimchi, sauerkraut, lacto-pickled vegetables, vegan yogurt. Lactic acid bacteria (Lactobacillus, Leuconostoc, Lactococcus) ferment anaerobically, converting sugars into lactic acid, which lowers the pH and preserves the food. Two levers: salt at 2–3% by weight, and keeping the food submerged below the brine.

3. Mycelium fermentation. Tempeh and aged vegan cheeses. Moulds grow root-like threads (hyphae) that weave through the substrate. Rhizopus oligosporus at 30–32°C for 24–48 hours binds soybeans into tempeh. Penicillium species produce vegan blue and rind cheeses.

4. Acetic acid fermentation. Kombucha, apple cider vinegar, coconut vinegar. Two stages: yeast converts sugar to alcohol, then Acetobacter (needs oxygen) converts alcohol to acetic acid. Kombucha's SCOBY is a symbiotic mat of both. Best at 22–28°C; 7–14 days for kombucha.

Four types. One principle: shape the environment, let the microbes do the work.

Two Common Mistakes

Almost every home-fermentation failure comes from one of two errors.

• Too little salt in lacto ferments. Below 2% and spoilage organisms win before LAB establish. Above 4%, and the LAB themselves are inhibited. 2–3% by weight is the safe band.

• Too much heat for tempeh or kombucha. Rushing above 35°C stresses the microbe and invites contamination. Warmth speeds ferments; heat kills them.

Fermentation rewards patience. It punishes hurry.

Is Fermented Food Better for You?

Three real benefits of a plant-based diet:

• Predigested anti-nutrients. Phytic acid in legumes, oxalates in some greens, and lectins in raw beans are reduced during fermentation. Minerals become more bioavailable.

• Added B vitamins and bioactive compounds. Levels vary — tempeh is not a reliable B12 source, contrary to older claims — but many other B vitamins increase.

• Live cultures for the gut. Unpasteurised ferments carry beneficial bacteria. Stanford research suggests regular consumption may support gut microbial diversity.

One useful layer in a plant-based diet. Not a substitute for one.

Frequently Asked Questions

What are the four main types of fermentation?

Yeast (alcoholic) fermentation, lactic acid fermentation, mycelium (mould) fermentation, and acetic acid fermentation. Each uses a different microbe and produces a different byproduct — alcohol and CO₂, lactic acid, mycelium networks, or acetic acid, respectively.

Is fermentation safe at home?

Properly executed fermentation is one of the safest food preservation methods. The acidic or alcoholic environment inhibits harmful bacteria. Trust the pH, the salt, and the smell — a ferment that smells rotten rather than tangy has failed and should be discarded.

What is the difference between lacto-fermentation and yeast fermentation?

Lacto-fermentation is anaerobic and produces lactic acid via bacteria — the source of sourness in sauerkraut, kimchi, and vegan yogurt. Yeast fermentation is often aerobic (at first) and produces alcohol and CO₂ — the source of bread rise and drink fizz.

Can plant milks be fermented like dairy?

Yes. Plant milks ferment readily with the same lactic acid bacteria used for dairy yogurt. Texture differs — soy sets firmest; oat and coconut are looser — but the microbiology is identical. Cashew milk fermented with rejuvelac produces a soft, aged vegan cheese.

Is tempeh fermented?

Tempeh is a fermented soybean cake made by inoculating cooked beans with Rhizopus oligosporus, a mould whose mycelium binds the beans into a firm block. Fermentation also breaks down some soy proteins, making them easier to digest.

Where Fermentation Goes Next

Reading about fermentation is one thing. Watching a tempeh block knit itself together overnight, or a jar of kimchi turn from sharp raw cabbage into something ancient — that is where the technique becomes intuitive.

At The Vegan School, the fermentation module runs sourdough, tempeh, kimchi, kombucha, and cultured vegan cheeses as hands-on practice. The principles above transfer directly. Once the four types are clear, every specific ferment is a small variation on one of them.