Tiny bit off-topic but please allay my curiousity since orthodoxy is so strong in south. Is bread not taboo? For orthodox Bengali brahmans, all "khambira-yukta" food, i.e. yeast-leavened food is taboo. All "sukta", a term applied to things that were sweet and have turned sour due to fermentation, is forbidden, except cow's milk yoghurt! Buffalo milk yoghurt is "sukta", and non.veg., cannot be used for rituals, and nor can that milk or its products! Goat milk ghee, aajya ghrta, is ok for ayurvedic formulations, not for food in general cases.
Idli fermentation is bacterial fermentation, Leuconostoc spp. in the first 8-10 hours, and less of wild yeasts, unless one keeps dosai batter for utthapams.
In Bengal, all bread was either baked by Portuguese, then Eurasian and later, Muslim bakers, all of whom were experts with yeasted dough. Hence, this type of raised bread, rusk or any yeasted product was a strict NO-NO, even in my childhood. When VERY sick, almost near death, a Bengali was given, pomegranate juice! That meant Yamaraja in the room! Yamaraja on the threshhold necessitated grapes, which in those days were very sweet and came from the northwest! Yamaraja in the knocking at the door meant apples! Mealy, overripe in the moist heat, apples signified you were truly ill! Also, barley water, an interesting concoction sworn to keep miserable Bengalis safe from the minions of Lord Yama. As soon as they were slightly better, they were dosed with a horrid herb, Centella, pennywort, cooked with a slim catfish, of 2 species, depending on how sick you were. No spices of course, and orthodox Bengalis eat fish, but no onions, garlic etc.! So imagine a terrible herb cooked with a slimy monstrous bearded barbed fish + evil head, eyes, and its black skin purely for health purposes, boiled with nothing to ward off smells, and being made to eat the concoction after being very ill for weeks. Sometimes death is more welcome, after the semi-rotten apples fed with great care, and you know how unaffordable those were, and now this!
aNNE! 
