Question

Fermentation of idli and dosa batter involves:

• A. Alcoholic fermentation only
• B. Lactic acid fermentation only
• C. Mixed lactic acid and alcoholic fermentation
• D. Acetic acid fermentation only

Hint:

Idli/dosa batter = LAB + Yeast. LAB gives sourness, yeast gives fluffiness (CO$_2$).

Answer 1

The Correct Option is C

Concept: Fermentation of idli and dosa batter is a complex biochemical process involving a mixed population of microorganisms, mainly lactic acid bacteria (LAB) and yeasts. These microorganisms work together (symbiotically) to produce both lactic acid and small amounts of alcohol, contributing to the characteristic taste, texture, and leavening of the batter.

Step 1: Understanding the microbial composition.
The batter typically contains:
• Lactic acid bacteria (e.g., Lactobacillus)
• Yeasts (e.g., Saccharomyces) These microorganisms originate naturally from raw ingredients like rice and urad dal.

Step 2: Role of lactic acid bacteria.
Lactic acid bacteria perform:
• Conversion of sugars into lactic acid
• Reduction in pH of the batter
• Development of sour taste

Step 3: Role of yeast.
Yeasts carry out:
• Alcoholic fermentation
• Production of carbon dioxide (CO$_2$) The CO$_2$ gas causes the batter to rise and become fluffy.

Step 4: Understanding the combined effect.
Since both:
• Lactic acid fermentation (by bacteria)
• Alcoholic fermentation (by yeast) occur simultaneously, the process is classified as mixed fermentation.

Step 5: Evaluating options.
• Option (A): Alcoholic fermentation only — Incomplete, ignores lactic acid production.
• Option (B): Lactic acid fermentation only — Incomplete, ignores yeast activity.
• Option (C): Mixed lactic acid and alcoholic fermentation — Correct.
• Option (D): Acetic acid fermentation only — Not involved in idli/dosa fermentation. Final Conclusion:
Fermentation of idli and dosa batter involves both lactic acid bacteria and yeast, resulting in mixed fermentation. Hence, the correct answer is option (3).