Fermented foods have become a wellness category, discussed in terms of microbiome benefits and sold at a premium.
Fermentation has been central to South Asian cooking for a very long time, for reasons that were practical rather than nutritional — preservation, digestibility, flavour and leavening without commercial yeast.
The major examples
Idli and dosa batters. Rice and urad dal, soaked, ground and left to ferment. The fermentation is driven by bacteria and wild yeasts present on the ingredients and in the environment.
What it accomplishes: leavening, producing the characteristic texture; acidification, which contributes flavour and inhibits spoilage; and breakdown of antinutrients, improving mineral availability.
The urad dal is not incidental. Its proteins contribute to the batter's ability to hold gas, and the combination with rice provides complementary amino acids.
Dhokla and khaman batters. Similar principle with different ingredients and regional technique.
Dahi. Yoghurt, made daily in a great many households, using a spoonful of the previous batch as starter. A continuous culture maintained across generations in some families.
Pickles. Many traditional preparations are genuinely fermented rather than simply preserved in acid — vegetables in salt, allowed to develop over weeks, with the salt selecting for lactic acid bacteria.
Kanji. A fermented drink from carrots or beetroot with mustard, common in northern winters.
Fermented preparations across the northeast, including fermented bamboo shoot, fermented soybean and fermented fish, which form a distinctive food culture with limited recognition elsewhere.
Toddy and traditional fermented beverages, with long histories in several regions.
Why fermentation developed
Not for the microbiome, which nobody knew about.
Preservation. In warm climates without refrigeration, fermentation extends the life of perishable food by creating an acidic environment hostile to spoilage organisms. This was the primary driver.
Digestibility. Fermentation breaks down complex carbohydrates and reduces compounds that cause digestive discomfort. Fermented pulse preparations are noticeably easier to digest than unfermented ones.
Nutrient availability. Reduction of phytates improves absorption of iron and zinc. Some B vitamins are synthesised by the organisms involved.
Leavening. Before commercial yeast, fermentation was how you made anything rise.
Flavour. The sourness, complexity and umami produced by fermentation are not incidental. They're substantially why these foods taste the way they do.
The health claims, weighed
Fermented foods are having a moment and the evidence is worth stating carefully.
A trial comparing a high-fermented-food diet with a high-fibre diet found that the fermented food arm increased microbial diversity and decreased several inflammatory markers, which is one of the more interesting recent findings in this area.
Observational evidence links fermented dairy consumption with various favourable outcomes, with the usual confounding caveats.
What's less established: that any specific fermented food produces specific health effects, or that the organisms in traditional ferments colonise the gut durably.
An important practical point: many commercially produced versions of traditionally fermented foods are pasteurised, which kills the organisms. If the live cultures are the point, that matters.
Fermenting at home
Practical notes, since conditions affect it enormously.
Temperature is the main variable. Idli batter ferments readily in warm conditions and struggles in cold ones. In cooler climates people use an oven with the light on, a warm cupboard, or extended time.
The starter matters for dahi. A small amount of an active previous batch, into milk cooled to lukewarm. Too hot kills the culture; too cold and it won't set.
Time is judged by state, not clock. Batter is ready when risen and smelling pleasantly sour. Over-fermented batter tastes unpleasantly acidic and loses its rise.
Salt in pickles is doing a job. Traditional quantities look alarming and they're selecting for the right organisms and inhibiting the wrong ones. Reducing salt substantially in a fermented pickle risks spoilage rather than preservation.
Cleanliness, not sterility. Clean equipment matters. Sterile conditions are neither achievable nor desirable, since you want the beneficial organisms to establish.
The point worth making
None of this is new, and framing traditional fermented foods as a wellness discovery gets the history backwards.
What's genuinely new is the explanation — understanding why practices developed empirically over centuries actually work.
That's worth something. It's also worth noticing that the practices existed and functioned perfectly well without it, and that the households making dahi daily were not waiting for validation.
Troubleshooting a batter that will not rise
The most common home fermentation problem and it usually has one of a few causes.
Too cold is the most frequent. The organisms are simply not active enough below a certain temperature, and the answer is a warmer spot and more time rather than more of anything.
Chlorinated water can inhibit the culture. Letting water stand uncovered for an hour before use, or using filtered water, resolves it where this is the issue.
Too much salt added before fermentation rather than after. Salt inhibits the organisms, which is why traditional practice adds it once the batter has risen.
And over-grinding, which heats the batter enough to damage the culture. Grinding in short bursts, with cold water, keeps the temperature down.
If none of those apply, the ingredients themselves may be the problem — very old dal ferments poorly, and some heavily processed rice lacks the surface organisms that traditionally started the process.