A ferment that is not bubbling

Bubbles are not the test

Carbon dioxide is a by-product of some of what is going on in a vegetable ferment, not the point of it. The point is acid, and acid is silent.

Several things can leave a perfectly healthy ferment looking still. Gas escapes as fast as it is produced if the lid is loose. A tightly packed jar holds bubbles in the mass where you cannot see them until you disturb it. Some vegetables — cucumber, carrot, beans — produce much less visible gas than shredded cabbage does. And the vigorous phase is short: a jar that bubbled hard on day three may be quiet on day seven and still working.

The reliable test is taste and smell. A working ferment gets steadily more sour. If it is more sour today than it was three days ago, it is fermenting, whatever the surface is doing.

Why it might genuinely have stalled

In rough order of how often each is the answer.

• The room is too cold. By far the commonest cause. Lactic acid bacteria slow dramatically in a cold kitchen, and a jar that would take five days in a warm room can take three weeks in an unheated one. It has not failed; it is going slowly.
• Too much salt. Salt slows the bacteria as well as their competitors. A heavy hand, or salt measured by spoon rather than weighed, can push a ferment into a crawl.
• Not enough time. The first day or two is often quiet while the population builds. Do not judge a jar before day three.
• Chlorinated water in the brine, in some cases. Leaving tap water to stand, or using filtered water, removes the question.
• The vegetables were not fresh. Long-stored or waxed produce carries fewer of the bacteria you are relying on. This matters most for a plain vegetable ferment with no starter.
• Everything was scrupulously sterilised. A vegetable ferment relies on the organisms already on the vegetable. Sterilising the produce itself removes the culture — clean jars, unsterilised vegetables.

What to do about it

1. Taste it. Sour and getting more so means it is working and needs no intervention.
2. Move it somewhere warmer — a normal warm room rather than a cold larder — and give it several more days.
3. Check the food is still fully under the brine, and top up with brine of the same strength if the level has dropped.
4. Give the jar a gentle tap or a small stir with a clean utensil, which often releases a mass of trapped gas and answers the question immediately.
5. If after a week in a warm room it has not become any more sour, and especially if it smells yeasty, sweet or of nothing, start again with weighed salt and fresh vegetables.
6. Throw it out rather than persevering if it smells putrid, has grown anything fuzzy, or has gone slimy and ropy.

What the jar is telling you

Getting sour

Working. The only sign that actually matters.

Cloudy brine

Working. This is what a population of bacteria looks like.

Bubbles, or fizz on opening

Working, and in the vigorous phase.

No bubbles but increasingly sour

Working. Either the gas is escaping or the phase has passed.

No bubbles and no change in taste after a week somewhere warm

Stalled. Start again.

Slimy, ropy brine or a putrid smell

Not a stall — a failure. Discard it.

Common questions