The discovery of fire was, anthropologists argue, among the single most game-changing discoveries in the history of humankind. Beyond its immediately visible help in warding off predators and its ability to transform metals into better hunting weapons, it is fire’s ability to gelatinise starch and denature proteins that essentially lifted homo sapiens out of the evolutionary battlefield of species a few hundred thousand years ago. It elevated us to higher ground, giving us a permanent advantage over every other living thing (barring the occasional pandemic bacteria and virus) for all foreseeable future.
Cooking makes meat easier to digest and grains edible. In a sense, cooking is digestion that happens outside your body, giving the process a head start and letting your body’s metabolism focus its efforts on more useful things—like the brain. But heat isn’t the only way to cook food. You can also cook food with acids. Peruvian ceviches, for instance, are essentially seafood cooked in an acid-like lime juice. Like heat, acids also denature proteins and keep away microbes, which is why we often take things that bacteria and fungi would love to eat and soak them in an acid-like vinegar, thus preserving them for longer than they would have otherwise lasted at room temperature.
There is, however, a third way to cook food, and that rather counter-intuitively involves the welcoming of the very microbes we work so hard to kill or keep away with heat or acids. The key here is to figure out which microbes you want while keeping the bad guys out. An uncharitable way to describe this is “strategic rotting”—or you could do what everyone does and call it “fermentation”, a word that goes back millennia to a Proto-Indo-European word meaning “to bubble or effervesce”, which is likely how we discovered this process. Wheat flour left with water starts to bubble as wild yeast, already present in the flour, breaks down starch in the wheat and turns it into sugars, and then eats the sugars to generate both carbon dioxide, which, well, effervesces, and humanity’s old friend in times of sadness and loss—alcohol.
Fast forward a few millennia, and we have mastered fermentation to the point where we can pick and choose microbes with precision and generate complex flavours in the bargain. So here is what you need to understand about fermentation to make it an integral part of your daily (and weekly, because some of these reactions take time) cooking routines. There is also significant recent evidence that eating fermented food, and thus the microbes that come with it, is good for gut health and has long-term positive health implications.
There are three kinds of fermentation reactions that are very useful to understand in the context of the Indian kitchen. The first one is fermentation by yeast, something that is pretty well understood in the context of baking bread. So, we will skip straight to the second one—lacto-fermentation. As the name suggests, it is fermentation using a family of bacteria that like to eat sugars (in starches) and turn them into carbon dioxide and lactic acid. The latter, like most acids, has a pleasant sour taste and, rather critically, helps keep other dangerous microbes away by creating an acidic environment.
The most common use of lacto-fermentation is to turn today’s milk into tomorrow’s yogurt using bacteria from yesterday’s yogurt. The key to getting this right is temperature. Milk that has been brought to a boil and then cooled down to 45 degrees Celsius works best for yogurt. In typically hot Indian summer conditions, this will take about four hours. It might take longer if your room temperature is lower.
But did you know that you can lacto-ferment literally anything? Try chopping some carrots into long thick sticks and let them soak in 2% salty water (100g of water with 2g of salt), ensuring that no part of the carrot is exposed to air. In 48-72 hours, lactobacteria will ferment the carrot, lending it a complex sour taste without its original sweetness. This makes for a fantastic condiment and is a more flavourful alternative to “pickling” carrots (or any vegetable) in an acid-like vinegar.
The reason we use salt is another fantastic example of human ingenuity. The varieties of lactobacteria that we are interested in have evolved a certain level of tolerance to salt, something that other dangerous microbes have not, which is why we use salt as a preservative in general. The salt helps keep the bad guys out while letting our friendly lactobacteria do their thing.
The third kind of fermentation is the use of a SCOBY—which stands for “symbiotic culture of bacteria and yeast”. In this method, it’s not just bacteria, but bacteria that have a seat-sharing alliance with certain kinds of yeast (which are fungi) that ferment your food. A good example of this is a ginger bug, a starter culture made by letting pieces of ginger (including the skin, which has the yeast and bacteria on it) sit in sugary water for a week. This starter can then be used to ferment any kind of fruit juice into a naturally carbonated (and mildly alcoholic) drink like ginger beer, watermelon ale or pineapple ale, etc.
The fermentation of rice and urad dal into idli batter uses the same principle described above. The urad dal has bacteria and yeast on its skin, and in the presence of a tiny bit of salt that keeps other microbes away, ferments into a bubbly and sour batter that can, depending on how sour it is, be used for idli, dosa or oothappam.
Without fermentation, there is no bread, and without bread there would have been no ancient Mesopotamia or Egypt. Without fermentation, milk will spoil, and without milk, there would have been no way to feed weaned babies, and without that there would be no civilisation. As American poet John Ciardi put it: “Fermentation and Civilization are inseparable.”
Krish Ashok is the author of Masala Lab: The Science Of Indian Cooking. @KrishAshok