First, a word on this dish
On paper, idli looks easy: a rice and lentil batter, steamed. In practice it is one of the dishes that humbles new cooks, because the result is decided overnight while the batter sits in a corner of your kitchen and you cannot step in once it has started. When it goes right, idli is soft, a little tangy, faintly sweet and springy under your finger. When it goes wrong, you get dense, pale pucks. So if your first batch turns out heavy, do not blame the steamer. Look back at the batter, because that is where almost every result is settled, and this recipe spends as many words there as it does on the steaming.
The story behind the dish
Tiffin is the South Indian word for light morning and afternoon dishes, and idli sits at the heart of it, most closely tied to Tamil Nadu and Karnataka. Historians do not agree on its beginnings. One camp points to a steamed fermented rice and lentil cake that existed in the South over a thousand years back. Another, which includes K.T. Achaya, raises the possibility of Indonesian influence, because early writing about a similar dish appears in the setting of trade between South India and Southeast Asia. This library leaves the question open instead of backing one answer. The safe statement is that for many centuries idli has been ordinary home food and temple food in the South, however the technique first reached the kitchen.
The method, in order
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Prep
Soak the rice and the dal apart
Wash the rice and leave it covered in water for 4 to 6 hours. In another bowl wash the urad dal together with the fenugreek seeds and soak those for the same time. Keep the two apart: the dal needs a long grind to become airy, while the rice does best with a coarser texture.
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Prep
Grind the dal until it is airy
Drain the dal and fenugreek and start the grinder with a small splash of cold water, adding more only when the blades struggle. Scrape the sides down every few minutes. Keep going until the batter is smooth, pale and clearly fluffier, about double the volume of the dry dal. That is 15 to 20 minutes in a wet grinder and a bit less in a strong blender. If it seems like too long, remember that the air you whip in now is what makes the idli soft later.
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Prep
Grind the rice to a rougher paste
Drain the rice and grind it on its own until it feels slightly sandy between your fingers rather than perfectly smooth. A bit of grain in the rice portion is welcome. Only the dal needs to be as fine and fluffy as you can get it.
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Prep
Mix and leave to ferment
Use your clean hand to blend the rice and dal batters in a roomy container; a machine would beat out the air you worked to add, and the batter will swell, sometimes to double its size or more. Rest a loose lid on top and put it somewhere that stays around 25 to 30°C (77 to 86°F) for 8 to 12 hours, which usually means overnight. In a chilly kitchen, set it in an oven with just the bulb on, or use the yogurt function of an Instant Pot.
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Prep
Judge the fermentation
Fermented batter looks higher than when you left it, has a slight dome and is dotted with bubbles, and it smells gently sour and yeasty without anything sharp about it. Now add the salt and fold it through softly. Stirring vigorously here deflates the batter.
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Cook
Steam the idli
Oil the idli moulds lightly and spoon batter into each cup until it is about three-quarters full. Place them over water that is boiling hard and steam for 10 to 12 minutes. Push a toothpick in; if it comes out clean and the surface bounces back under a light press, they are cooked.
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Serve
Pause, then release them
Do not unmould straight away. Give the idli 2 to 3 minutes to rest, because they tighten up as they cool, and then they come away neatly with a spoon dipped in water. Eat hot, with coconut chutney and sambar.
Ingredient stand-ins
The usual ratio is 3 parts rice to 1 part urad dal, and it works reliably; a few families push it to 4 to 1 for a denser result. If fermentation worries you, idli rava, a coarse grit of parboiled rice, can replace whole rice, and it is more forgiving because it is already processed. Fenugreek is optional, yet it helps taste and fermentation, so include it when you can.
Making it milder or fiercer
Idli carries no spice of its own. What it offers is texture and a light sourness, and all the heat comes from the chutney and sambar on the side, which you can make as mild or as hot as you like without changing the idli at all.
The slip most cooks make
Batter that refuses to rise usually comes down to a cold kitchen, dal that was not ground until airy, or salt added too early, since salt can slow fermentation down; that is why it goes in at the end here. If the batter did rise but your idli are still flat and heavy, suspect a dal grind that stayed too coarse, or stirring the fermented batter too hard so the air escaped. And if the idli cling to the moulds, either the moulds were not greased well or you took them out before they had rested.
Storing what is left
Fridge or counter: Refrigerate the fermented batter for 4 to 5 days. Souring does not stop in the cold, only slows, so what you cook on day four will be tangier and looser than what you cook on day one. Leftover idli stay good for 2 to 3 days in a lidded container in the fridge.
Bringing it back to life: A few minutes in the steamer, 3 to 4, makes cold idli tender again. Alternatively, cover them with a damp paper towel and microwave for a short time so they do not dry out. Idli that has already gone hard will not come back well without extra moisture.
Handle with care
Well-fermented batter is not the same thing as spoiled batter, and your nose is the best guide. A pleasant sour, slightly yeasty smell with even bubbles means fermentation is working. A rotten or alcohol-like smell, a change in colour, or any mould means the batter has gone bad and you should throw it out instead of steaming it. Leave the container loosely covered, not airtight, because trapped gas can build up, and keep it away from anything that could contaminate it. Move it to the fridge once it has fermented as far as you want it to.
Sources worth opening
- K.T. Achaya, "Indian Food: A Historical Companion" (Oxford University Press) — on the debated early history and possible Southeast Asian influence on fermented rice-and-lentil cakes.