Three vessels, one process, but not the same bacteria
Idli batter, kanji, and curd all ferment, but they are not running the same biological programme. Idli batter is a mixed fermentation: Leuconostoc mesenteroides starts the process in the first few hours, producing carbon dioxide that makes the batter rise, then Lactobacillus species take over and produce lactic acid that drops the pH and sets the sour note. Kanji, the fermented black carrot drink common in northern India, especially around Holi, uses wild bacteria from the carrot skin surface and the mustard seeds added to it, primarily Lactobacillus plantarum. Curd is simpler: a controlled inoculation of Lactobacillus bulgaricus and Streptococcus thermophilus from the spoon of yesterday's curd converts lactose into lactic acid, which causes the milk proteins to coagulate. Same category, three distinct microbial casts.
