Lacto-Fermentation
Lacto-fermentation is a preservation method in which lactic acid bacteria, already present on fresh produce, convert sugars into lactic acid in a salty, oxygen-free environment. The acid gives sauerkraut, kimchi, and traditional dill pickles their sour, complex flavour and keeps them safe to eat for months.
How it works
The "lacto" refers to lactic acid bacteria, mainly species in the Lactobacillus, Leuconostoc, and Pediococcus groups, not to milk.
Each ingredient has a job:
- Salt draws water and sugars out of the vegetables by osmosis, creating a brine. It also slows spoilage microbes while salt-tolerant lactic acid bacteria keep going.
- Submersion keeps out oxygen, which mould and many spoilage organisms need.
- Lactic acid bacteria eat the released sugars and produce lactic acid, along with carbon dioxide and flavour compounds.
Different bacteria take over in waves. Gas-producing Leuconostoc species often dominate early, then acid-loving Lactobacillus species finish the job, dropping the pH to around 3.5.
Salt ratios
Always measure salt by weight.
| Ferment | Salt |
|---|---|
| Sauerkraut, shredded vegetables | 2% of vegetable weight (20 g per kg) |
| Mixed vegetables in brine | 2–3% of vegetables + water |
| Kimchi (salting the cabbage) | Brine or dry salt, then rinsed; ~2–3% final |
| Whole cucumber pickles | About 3.5–5% brine for crunch |
Use non-iodized salt without anti-caking agents, such as pickling or kosher salt, for clearer brine. See kosher salt vs table salt.
Temperature and time
The sweet spot is 18–22 °C (64–72 °F). Warmer ferments are fast but often soft and less complex; cooler ones take longer but taste cleaner and stay crunchier.
- Quick vegetables and hot sauce mash: 3–7 days
- Kimchi at room temperature: 1–5 days, then refrigerated
- Sauerkraut: 2–6 weeks
Once it tastes right, refrigerate to slow fermentation almost to a stop.
Chef Fizz says: Weigh down your veggies with a small zip bag full of brine. If it leaks, it just adds more brine.
Is it safe?
Properly made lacto-fermented vegetables have an excellent safety record. The rapid drop in pH, below 4.6 and usually much lower, prevents dangerous bacteria like Clostridium botulinum from growing.
Signs something has gone wrong:
- Discard: fuzzy mould in any colour, pink or slimy brine with a rotten smell, or mushy vegetables that smell putrid.
- Usually fine: cloudy brine, bubbles, a white sediment, or a flat white film (kahm yeast) that you can skim.
Common mistakes
- Too little salt. Vegetables soften and spoilage organisms can win.
- Vegetables poking above the brine. Exposed pieces mould first.
- Sealing tightly without venting. Carbon dioxide builds pressure. Use an airlock lid or loosen ("burp") the jar daily.
Questions
What salt percentage should I use for lacto-fermentation?
For shredded vegetables like sauerkraut, use 2% salt by weight of the vegetables, or 20 g per kilogram. For whole vegetables in brine, use 2–3% of the combined weight of vegetables and water, or about 3.5–5% for crunchy cucumbers in a plain brine.
Is the white film on my ferment mould?
A flat, white, wrinkly film is usually kahm yeast, which is harmless but tastes off. Skim it. Fuzzy, raised spots that are blue, green, black, or pink are mould, and the batch should be discarded.
Does lacto-fermentation use dairy?
No. The 'lacto' refers to lactic acid and the Lactobacillus family of bacteria, not milk. Lacto-fermented vegetables are dairy-free.
How do I know when my ferment is done?
Taste it. It's ready when it's pleasantly sour, which often takes 3–7 days for quick ferments and 2–6 weeks for sauerkraut. A pH of 4.6 or lower is safe; most finish around 3.5.