How to lacto-ferment chillies in brine or as a salted mash for hot sauce: salt percentages by weight, temperatures, how long to wait, and how to tell harmless yeast from mould.
How it works¶
Lacto-fermentation relies on lactic acid bacteria that live naturally on the skins of vegetables. In a salty, airless environment they thrive while most spoilage organisms are held back. They convert sugars into lactic acid, which lowers the pH, sours and deepens the flavour, and preserves the chillies. The same process underlies sauerkraut and kimchi, and many commercial hot sauces, including some versions of sriracha-style sauces and the mash behind Tabasco, which is aged for years.
Fermentation mellows raw chilli heat into something rounder and more complex. It does not reduce capsaicin meaningfully.
Salt: always by weight¶
Salt percentages are the part that matters for safety and consistency, so weigh everything in grams. Use non-iodised salt (sea salt, kosher salt, pure fine salt); iodine and anti-caking agents can inhibit the bacteria or cloud the brine. Use unchlorinated water: filtered, bottled, or tap water that has stood uncovered overnight.
Brine method (3–5%)¶
Chillies are submerged in salt water. The percentage is usually calculated on the water, or on water plus chillies for a gentler brine.
Salt (g) = weight of water (g) × 0.035 for a 3.5% brine, a good middle value.
| Water | 3% | 3.5% | 5% |
|---|---|---|---|
| 500 g (500 ml) | 15 g | 17.5 g | 25 g |
| 1 kg (1 litre) | 30 g | 35 g | 50 g |
Lower percentages ferment faster and taste less salty but give less protection; higher percentages are slower and safer in warm weather.
Mash method (2–3%)¶
Chillies (and garlic, onion or fruit) are blended or chopped, then mixed with salt, and ferment in their own juice.
Salt (g) = weight of prepared chillies and other ingredients (g) × 0.025
For 500 g of chilli mash, 12.5 g salt gives 2.5%.
Method (brine)¶
- Wear gloves when cutting hot varieties (see handling-chillies-safely).
- Prepare the chillies. Remove stems. Leave small chillies whole with a slit in each, or slice larger ones. Add aromatics if you like: garlic, ginger, onion, carrot.
- Pack a clean jar, leaving at least 3–5 cm headspace.
- Dissolve the salt in the water and pour over until everything is covered.
- Weigh the chillies down under the brine with a glass fermentation weight or a small water-filled bag. Anything poking above the surface can grow mould.
- Cover with an airlock lid, or a lid screwed on loosely. A tight lid can build dangerous pressure; if you use one, "burp" it daily.
- Ferment at 18–24°C, out of direct sun, on a tray to catch overflow.
- Watch it. Bubbles usually appear within 1–3 days, and the brine turns cloudy. Activity peaks in the first week, then slows.
- Taste after a week. Most chilli ferments are ready in 1–4 weeks: pleasantly sour, softened, with no raw bite.
- Make sauce. Drain (keep the brine), blend the chillies with enough brine to reach the texture you want, and optionally add vinegar, fruit or sugar. Strain for a smooth sauce.
Safety and acidity¶
A successful ferment reaches a pH of roughly 3.5–4.0. Food-safety guidance treats a pH of 4.6 or below as the threshold that prevents Clostridium botulinum from growing. Inexpensive pH strips or a meter take the guesswork out; adding vinegar to the finished sauce is an easy way to push the pH lower. Store the finished sauce in the fridge, where it keeps for months.
🛟 White film on the surface
A flat, white, wrinkly film is usually kahm yeast: harmless, though it can taste musty. Skim it off and make sure everything is submerged. Mould is fuzzy and raised, often blue, green, black or pink. If you see fuzzy mould, particularly anything other than a small spot on an exposed piece, discard the whole batch; mould can send roots and toxins through soft food. When in doubt, throw it out.
🛟 Slimy brine or rotten smell
A ferment should smell sour, sometimes funky, never putrid. Slimy, rotten-smelling or strangely coloured ferments have gone wrong, usually from too little salt, too much heat or exposed produce. Discard and start again with correct salt by weight.
Varieties to try¶
Jalapeños and serranos for green sauce; habanero or scotch-bonnet with mango or pineapple; red cayenne-type chillies for a Louisiana-style sauce; aji-amarillo for fruity yellow sauce. For Korean fermented chilli paste, which uses a different, grain-based process, see gochujang.