Techniques · 3 min read ·
How to Ferment Dosa and Idli Batter (Even in Cold Weather)
Why dosa and idli batter won't rise, and how to fix it: the right rice and dal ratio, grinding tips, the ideal temperature, how to ferment in winter or a cold climate, and how to tell when the batter is ready.
The most common question from anyone trying dosa or idli at home is: why didn’t my batter rise? Fermentation sounds mysterious, but it follows a few simple rules. Get them right and you’ll have light idli and crisp dosa every time.
What fermentation does
contains no yeast. Natural microbes, already present on the rice, dal and your hands, feed on the starches overnight and produce gas and a little acid. The gas makes the batter rise and turn bubbly; the acid gives the pleasant sourness. Urad dal is the key ingredient: when ground well, it becomes sticky and traps the gas, a bit like gluten does in bread.
The basic ratio
- For idli: 3 parts rice to 1 part whole skinless urad dal.
- For dosa: 4 parts rice to 1 part urad dal, plus a teaspoon of fenugreek seeds.
Parboiled (sela) rice gives the softest idli; ordinary rice works for dosa. Fenugreek seeds help fermentation and give dosa its golden colour.
Grinding
- Soak rice and dal separately for 5–6 hours.
- Grind the urad dal with ice-cold water, a little at a time, until it’s light, fluffy and almost doubled. This is the most important step.
- Grind the rice slightly coarser, like fine semolina, for idli; smoother for dosa.
- Mix by hand. Many cooks swear the warmth and natural microbes of your hand help fermentation.
- Add salt before fermenting in warm weather; in cold weather, some add it after, as salt slows fermentation slightly.
Temperature is everything
Batter ferments best at 25–35°C. In South India’s heat it rises in 6–8 hours. In a cold kitchen, below about 20°C, it may barely move even after 24 hours. Here’s how to keep it warm:
- Oven with the light on: the most reliable method. Put the batter in a switched-off oven with only the light on. The bulb keeps it at about 30°C.
- Near a warm appliance: on top of the fridge, near a radiator or water heater.
- Wrapped: put the bowl in a box, wrap it in a blanket or towel.
- Instant Pot: use the yogurt setting on low for 8–10 hours.
How to tell it’s ready
A well-fermented batter:
- has risen to nearly double,
- is full of small bubbles on top and inside,
- smells pleasantly sour, not unpleasant or alcoholic,
- feels light and airy when stirred.
Stir gently once before using; don’t beat out all the air.
Troubleshooting
- Didn’t rise: too cold, or the urad dal wasn’t ground fluffy enough. Move somewhere warmer and wait.
- Too sour: over-fermented in hot weather. Use it for uttapam, or mix in a little fresh rice flour.
- Flat, hard idli: under-fermented or batter too thin.
- Dosa sticks: the pan isn’t seasoned or hot enough; the batter itself is usually fine.
Storing
Fermented batter keeps for 3–4 days in the fridge and gets a little more sour each day. Take out what you need and let it come to room temperature before cooking.
Once you’ve got the hang of it, one batch gives you a week of breakfasts: masala dosa, idli, uttapam and more. See our South Indian breakfast guide for a weekend plan.
