How to ferment vegetables in brine

Read this first

FoodHQ explains how fermenting works and what to do at the worktop. It does not publish the numbers.

Salt concentration, acidity and keeping times are the things that decide whether a ferment is safe, they vary by vegetable and by method, and they are set by food safety authorities rather than by cookery writers. FoodHQ does not publish salt percentages, pH figures or keeping times for home preserving. Those are safety numbers, they are set by a food safety authority rather than by a cookery writer, and the right ones depend on what you are fermenting and where you are. In the UK the Food Standards Agency is the authority — use a recipe from them or from another body with the same standing, and treat this page as the explanation of why that recipe is shaped the way it is.

So: get your salt figure and your timings from an FSA recipe or one of equivalent standing, and use this page to understand what those numbers are doing and how to tell whether your jar is behaving.

The method, and what each step is for

1. Choose fresh, firm vegetables. Freshness governs the final texture more than anything you do later, and the bacteria you are relying on live on the surface of the vegetable itself.
2. Wash them, do not sterilise them. Rinse off soil. Do not scrub with anything antibacterial and do not blanch them — you would be removing the culture that does the work. The jar and the weight should be clean; the vegetables should not be sterile.
3. Trim where it matters. Cut the blossom end off cucumbers, a few millimetres. That end carries the enzymes that soften a ferment.
4. Pack the jar, leaving headspace. Firm but not crushed, with a few centimetres of room at the top. A jar filled to the rim will push brine out as it works.
5. Add the salt. Either dissolved in water as a brine, or rubbed through shredded vegetables so they make their own liquid. Weigh it. Salt measured by spoon varies by up to half depending on the crystal, and this is the number that matters most.
6. Add aromatics if you want them. Dill, garlic, peppercorns, mustard seed, bay, horseradish. Tannin-bearing leaves — blackcurrant, oak, grape, horseradish — also help keep things crisp.
7. Submerge everything and weight it down. Nothing may float. This is the step people skip and it is the one that causes most failures.
8. Cover so gas can leave and air cannot enter. An airlock lid, or an ordinary lid loosened once a day. Never fully sealed and forgotten.
9. Leave it somewhere cool and out of direct sun, on a plate to catch overflow.
10. Taste it every few days with a clean utensil and refrigerate when it tastes the way you want. Cold does not stop it but slows it to a crawl.

What you will see, and what it means

• Cloudy brine. Normal, and a good sign. It is bacteria.
• Bubbles, fizz, a hiss on opening. Normal. Carbon dioxide.
• A sour smell that gets stronger. Normal, and the thing you are actually waiting for.
• Brine overflowing. Normal in the first days. Stand it on a plate.
• Colour fading or shifting. Normal — cucumbers go from bright to olive, red cabbage bleeds pink into the brine.
• A flat white film on top. Kahm yeast. Harmless, tastes bad, skim it and re-submerge everything.
• Fuzzy, raised, coloured growth. Mould. Discard the batch — see mould on a ferment.
• Slimy, ropy brine, or a putrid rather than sour smell. Discard.

Vegetables, and how they behave

Cabbage

The most forgiving, and the usual place to start. Dry-salted rather than brined — it makes its own liquid.

Cucumber

Classic and the most texture-sensitive. Small, fresh, firm cucumbers, blossom end trimmed, tannin leaves in the jar.

Carrot, radish, turnip, beetroot

Sturdy, reliable, slow. Cut into batons or leave small ones whole.

Green beans, cauliflower, courgette

Work well. Courgette softens faster than the others.

Garlic, chilli, onion

Ferment readily and are excellent as a seasoning ingredient afterwards.

Anything already soft or over-ripe

Will not improve. Fermenting preserves texture, it does not restore it.

Common questions