Vegetables ferment
Kimchi (napa cabbage)
Salted napa cabbage coated in a chilli, garlic, ginger and often fish-sauce paste, fermented briefly then kept cold.
- Temperature
- 1–22 °C
- Short start at cool room temperature, then refrigerate at about 1–4 °C.
- Time
- 1–2 days at room temperature, then weeks in the fridge
- Young kimchi is crisp and fresh; older is sour and best for cooking (stews, fried rice).
- Salt
- Finished kimchi is typically around 2–3% salt
- There is no USDA/NCHFP tested kimchi recipe; follow a trusted recipe's salting and do not cut salt significantly. Check that it sours.
- Acidity (safety control)
- pH 4.6 or below — ideally under 4.0 before cold storage
- Acid made by lactic bacteria is what keeps vegetable ferments safe; 4.6 is the regulatory boundary for acid foods. Check with pH strips (narrow range) or a calibrated meter. Smell and taste are not a safety test.
Timeline
Stage 1: Salt the cabbagestart · about 6 h
Hands-on — Turn now and then
Stage 2: Paste & packfrom 6 h · about 2 h
Hands-on — Press out air
Stage 3: Room-temperature startfrom 8 h · about 36 h
Fermenting / waiting — Cool room, about 1–2 days
Stage 4: Cold fermentfrom 44 h · keeps about 6 weeks
Cold storage — Fridge 1–4 °C; flavour develops
Ingredients
- Napa cabbage
- Coarse salt for brining
- Paste: gochugaru, garlic, ginger, spring onion, fish sauce or salted shrimp (or a vegan alternative), a little sugar or rice paste
- Radish (optional)
Equipment
- Large bowls
- Gloves (chilli)
- Glass jars or a kimchi container
- Kitchen scale
Steps
- Salt or brine the cabbage until it bends without snapping (several hours), turning it.
- Rinse thoroughly and drain well.
- Mix the paste and rub it between the leaves.
- Pack tightly into a clean jar, pressing out air; leave headspace for gas.
- Leave at cool room temperature for about 1–2 days, pressing down daily, until it smells sour and tastes tangy.
- Move to the fridge and let it keep developing.
Is it working?
- Sour, fresh, garlicky smell
- Small bubbles; brine rises
- Cabbage still crisp-tender
Smell & texture: Sharp, sour, pungent with garlic and chilli — strong is normal. Crisp leaves; fizzy tingle as it ages.
Signs tell you it's fermenting, not that it's safe: never rely on smell or appearance alone.
Safety, mould and discard rules
Mould or yeast?
A thin, flat, white or cream film on the brine surface is usually kahm yeast: skim it off promptly, because it feeds on the acid and can raise the pH. Anything fuzzy, raised, or coloured (blue, green, black, pink, orange) is mould: discard the whole batch, including the brine. If you can't tell which it is, discard.
Storage
Refrigerated, tightly packed and pressed under its brine. Open jars carefully: gas builds up.
Shelf life: Refrigerated kimchi keeps developing for weeks to a few months; it gets sourer and softer. Kimchi with raw seafood is best eaten sooner. Not shelf-stable.
The science: what's happening
Brining wilts the cabbage and seeds the right environment for salt-tolerant lactic bacteria (notably Leuconostoc and Weissella in kimchi). A short warm start gets acid production going; long cold storage lets it sour slowly and develop flavour and fizz.
Organisms
- Leuconostoc species
- Weissella species
- Lactobacillus and related species as it sours
Troubleshooting
- Too salty
- The cabbage wasn't rinsed well. Add sliced radish or fresh cabbage; it mellows over time.
- Overflowing jar
- Leave more headspace and press down daily during the warm start.
- Too sour
- Cook with it: kimchi-jjigae, kimchi fried rice, pancakes.
A dish (not a ferment) gone wrong? Try Recipe Rescue.
Cook with it
Learn more
Sources
- General Information on Fermenting — National Center for Home Food Preservation
- Potential Hazards with Fermented Foods — Association of Food and Drug Officials
- 21 CFR Part 114 — Acidified Foods (pH 4.6 boundary) — US Code of Federal Regulations (eCFR)
Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.