Grain & dough ferment

Dosa batter

Beginner

Soaked rice and urad dal ground smooth and fermented overnight until bubbly and sour.

Temperature: 25–32 °C; Cold kitchens may need 24 hours or an oven with the light on.
Time: 8–14 hours in a warm kitchen (up to about 24 h when cool); Ready when roughly doubled, bubbly and pleasantly sour.

Timeline

Stage 1: Soakstart · about 5 h
Fermenting / waiting — 4–6 hours
Stage 2: Grind & mixfrom 5 h · about 1 h
Hands-on — Cold water keeps it from overheating
Stage 3: Fermentfrom 6 h · about 12 h
Fermenting / waiting — 25–32 °C
Stage 4: Refrigeratefrom 18 h · keeps about 4 days
Cold storage — 3–5 days

Ingredients

Rice (raw or a mix with parboiled) and whole/split urad dal, about 3:1 to 4:1
A few fenugreek (methi) seeds
Salt
Water

Equipment

Wet grinder or strong blender
Large bowl with room to double

Steps

Soak rice and dal (with methi) separately 4–6 hours.
Grind dal to a fluffy paste with cold water; grind rice slightly grainy.
Mix by hand with salt into a thick pouring batter.
Cover loosely and ferment in a warm place until risen and bubbly.
Stir down; thin with water for dosa.
Refrigerate leftovers.

Is it working?

Risen (often doubled) with a domed, bubbly top
Pleasantly sour smell
Light, aerated texture when stirred

Smell & texture: Clean, tangy, yeasty. Gets sourer each day in the fridge.

Signs tell you it's fermenting, not that it's safe: never rely on smell or appearance alone.

Safety, mould and discard rules

Mould or yeast?

A dry crust on top is just dried batter — scrape it off. Coloured spots or fuzz are mould: discard the whole batch.

Storage

Refrigerate after fermenting.

Shelf life: About 3–5 days in the fridge.

The science: what's happening

Lactic bacteria (from the dal, rice and your hands) acidify the batter while yeasts and heterofermentative bacteria make gas, so it rises and turns pleasantly sour. Urad dal's mucilage traps the bubbles.

Organisms

Leuconostoc mesenteroides
Lactic acid bacteria (Enterococcus, Lactiplantibacillus)
Wild yeasts

Troubleshooting

Didn't rise: Too cold or batter too thin. Put it somewhere warm (an oven with the light on) and give it more time.
Too sour: Shorter ferment or fridge sooner; thin with a little fresh ground rice.

A dish (not a ferment) gone wrong? Try Recipe Rescue.

Cook with it

Masala dosa

Learn more

Sources

Potential Hazards with Fermented Foods — Association of Food and Drug Officials

Guidance changes: check the source for current wording. Original text; figures quoted from the sources where stated.