This question was asked on General knowledge program.
Question
When idli is baked on steam, it gets softer and pluffy . Get holes in it. Why??
1. Starch changes to fat
2. Protein changes to gluten
3. Production of acid and gases
4. Steaming of water
Answer
We will look into each option
Option 1: Starch changes to fat -
- In idli batter, rice has starch.
- Starch does NOT become fat on steaming.
- Starch becomes soft and sticky on heating - we call it *gelatinization*. It makes idli soft, but it does NOT make holes.
- So this is half-true, but not main reason for holes.
Option 1 ruled out !!!
Option 2: Protein changes to gluten
- Gluten is only in Wheat, Maida, Rava
NOT in Rice and Urad Dal.
- Idli has NO gluten at all.
That's why idli is gluten-free food.
- Urad dal protein makes idli hold shape,
but it never becomes gluten.
Option 2 ruled out !!!
Option 3: Production of acid and gases -
This is the real science. Happens in 2 steps:
*Step 1 - Fermentation (Night before):*
We keep batter overnight.
Good bacteria _Lactobacillus_ and yeast eat sugar in rice/dal.
They produce:
- *Lactic Acid* -> Gives idli its slight sour taste
- *Carbon Dioxide Gas (CO2)* ->
Gas makes tiny bubbles in batter. Batter rises up, becomes fluffy.
*Step 2 - Steaming (Morning):*
When we steam it, heat makes those CO2 bubbles EXPAND like balloon.
Bubble expands -> bursts -> leaves a HOLE behind.
Thousands of tiny holes = Spongy, soft idli.
No gas = No holes
Hard, flat idli like stone. That's why unfermented batter makes hard idli.
Option 4: Steaming of water
- Yes, steam cooks idli. Steam makes it hot.
- But steam alone cannot make holes. If we steam plain rice paste without fermentation, we get hard rice cake, not soft idli !!!!
- Steam is just the cooking method, not the reason for holes.
Option 4 ruled out !!!
> *Final Answer : Option 3*
> *Idli soft + holes = Because fermentation produces acid + CO2 gas, and steam expands that gas.*
