Salt, time and cabbage: how fermented vegetables were invented everywhere

Before refrigeration, the autumn problem was universal in temperate regions: a large quantity of vegetables arriving at once, and several months before anything fresh would grow again.

The solution arrived at across an enormous range of unconnected cultures is the same. Salt the vegetables, keep them under liquid and away from air, and wait.

The mechanism

Lactic acid bacteria are already present on vegetables. Salt draws water out through osmosis, creating a brine, and it suppresses many organisms while the lactic acid bacteria tolerate it comparatively well.

Those bacteria consume sugars in the vegetable and produce lactic acid. The acid drops the pH, which suppresses spoilage organisms further and eventually limits the fermentation itself. Submersion excludes oxygen, which excludes the moulds and yeasts that would otherwise grow on the surface.

The result keeps for months, tastes markedly different from the raw vegetable, and — usefully — retains vitamin C, which mattered enormously in populations with no fresh produce over winter.

No starter culture is needed. The organisms are already there. This is why the technique could be discovered independently: it happens if you salt vegetables and leave them.

The regional versions

Sauerkraut across central and eastern Europe: shredded cabbage, salted, weighted under its own brine, fermented for weeks. Simple to the point of austerity, and the base of an enormous number of dishes.

Kimchi in Korea, which is not one thing but a large family. The best-known version involves brining napa cabbage, then coating it with a paste of chilli, garlic, ginger, salted seafood and other ingredients, and fermenting. Regional and seasonal variants number in the hundreds, and the communal preparation in late autumn is a social institution in its own right.

Suan cai and paocai in China, mustard greens and mixed vegetables in brine, with regional traditions across the country.

Torshi across the Middle East and the Balkans, a broad family of pickled vegetables, some fermented in salt brine and some in vinegar.

Achar in South Asia, where the preserving agents include salt, oil, spice and sun exposure, and the fermentation profile is different again.

Tsukemono in Japan, an enormous category using salt, rice bran, miso, sake lees and other media, with quite different results from each.

Salt concentration is the main variable

Higher salt slows fermentation and favours a narrower range of organisms, giving a sourer, saltier result that keeps longer. Lower salt ferments faster, tastes milder, and is more prone to going wrong.

Traditional recipes generally specify salt by proportion of vegetable weight, and the range across traditions is wide. Regions with hot climates tend toward higher salt for obvious reasons.

Temperature does similar work. Cool fermentation is slow and produces a cleaner, more complex result; warm is fast and can turn soft or off. Most traditions ferment in cool cellars, buried pots or, in Korea, in vessels sunk into the ground.

Fermented is not the same as pickled

A useful distinction that gets blurred in English.

Fermented vegetables become sour because bacteria produce acid inside the jar. Vinegar pickles become sour because acid was added. The processes are different, the microbiology is entirely different, and the flavours are distinguishable — fermented products have a complexity that vinegar pickles do not.

Industrial production largely replaced fermentation with vinegar and pasteurisation, because it is faster, more consistent and shelf-stable without refrigeration. A great many people's experience of sauerkraut is a pasteurised vinegar product that shares a name with the thing and not much else.

What was known before microbiology

None of these traditions knew about bacteria. What they had was extremely precise procedural knowledge: how much salt, which vessel, how to weight the contents down, what the surface should look like, what a bad batch smells like, when to move it somewhere colder.

That knowledge was accurate without being explanatory, which is the normal condition of traditional technique. The explanation arrived in the nineteenth century and changed very little about the practice.

Why the interest has returned

Partly flavour, partly the current attention to gut microbiota, and partly because home fermentation is one of the few food processes that is genuinely cheap, requires no equipment and works reliably.

The health claims run ahead of the evidence in places. That fermented foods contain live organisms is straightforwardly true; what those organisms do once eaten, and how much of the effect is from the bacteria versus the vegetables, is an active research area rather than a settled one.

What is not in doubt is the original point of the exercise. A barrel of cabbage salted in October is food in February, and for most of history that was the whole argument.