Tamil Nadu and Karnataka — the idli is believed to have evolved from the Indonesian kedli-concept brought through trade routes; its mention in 10th century Kannada literature pre-dates the modern form
Idli is the paradigmatic South Indian steamed fermented cake — rice and urad dal batter fermented overnight, then poured into dimpled moulds and steamed until firm and springy. The science of idli involves the specific activity of two fermentation agents: Leuconostoc mesenteroides (the primary lactic acid bacterium in the rice) and Enterococcus faecalis (in the urad dal), which work together to produce the CO₂ that makes idli spongy. The idli must steam without interruption for 10–12 minutes — opening the steamer prematurely collapses the structure. A properly made idli is white, soft, slightly spongy, and pulls away cleanly from the mould without sticking.
With sambar and coconut chutney, served hot from the steamer. The contrast of the hot soft idli against the room-temperature coconut chutney is structural.
{"Urad dal must be ground to an extremely smooth, aerated paste — the aeration traps CO₂ during fermentation","Rice (idli rice, a parboiled short-grain variety) ground to a coarser, slightly grainy paste — the grain of the rice provides the idli's characteristic texture","Ferment at 28–32°C for 12–16 hours until the batter has risen and smells pleasantly sour","Do not stir the fermented batter — stirring deflates the air bubbles responsible for spongy texture","Steam without interruption and do not open the steamer — temperature drop collapses the rising structure"}
The Tirunelveli tradition uses a 4:1 idli rice to urad dal ratio (more dal than normal) for an extremely soft idli. The Chettinad tradition uses a different variety of parboiled rice entirely (kar rice) which produces an off-white idli with a firmer, more pronounced texture. The test of a perfect idli: it should hold its dimple shape but yield when pressed, returning slowly.
{"Stirring fermented batter — deflates it and produces flat, dense idli","Under-fermented batter — flat, hard, no sponge structure","Opening steamer during cooking — the partial pressure release causes the idli to collapse in the mould"}