Idli fermentation microbiology: Which organism is present in the initial stages of natural idli batter fermentation (soaked rice and black gram)?

Introduction / Context:
Idli is a traditional South Asian steamed cake made from a fermented batter of rice and dehulled black gram (urad). The microbial succession during soaking and grinding creates leavening, acidification, and flavor. Recognizing early colonizers explains gas formation and pH drop that set the stage for lactic acid bacteria.

Given Data / Assumptions:

• Batter is fermented spontaneously from microorganisms on grains and equipment.
• Initial organisms drive early CO2 formation and slight acidity at ambient temperatures.
• Later stages are dominated by lactic acid bacteria that stabilize acidity and texture.

Concept / Approach:
Leuconostoc mesenteroides (a heterofermentative lactic bacterium) commonly appears early, producing CO2, lactic acid, and flavor compounds. This gas creates aeration in batter. As fermentation proceeds, Lactobacillus species (e.g., L. plantarum) increase acidification and contribute to texture and shelf-life. Molds like Aspergillus niger are not part of desired batter flora, and Bacillus natto pertains to soybean fermentation.

Step-by-Step Solution:
Identify early heterofermentative LAB in cereal-pulse fermentations. Connect CO2 production and mild acidity to Leuconostoc mesenteroides. Exclude molds and unrelated Bacillus fermentations. Select L. mesenteroides as the initial organism.

Verification / Alternative check:
Studies of idli batter show early dominance by Leuconostoc spp., followed by Lactobacillus spp.; gas bubble formation corresponds with heterofermentation.

Why Other Options Are Wrong:

• Aspergillus niger: Environmental mold; not desired in idli batter.
• Bacillus natto: Soybean fermentation organism; not typical in idli.
• Lactobacillus plantarum: Important later but not the earliest dominant.
• None of these: Incorrect because L. mesenteroides is correct.

Common Pitfalls:
Attributing early batter aeration to yeasts alone; in idli, heterofermentative LAB play a key role in gas formation.

Final Answer:
Leuconostoc mesenteroides predominates in the initial stage of idli fermentation.