Question

Why does dough left open for few days starts to emit a foul smell

Answer 1

Wheat dough when kept in open for few days, following activities takes place:
                1. formation of fungus
                2. reproduction of yeast
 These fungus and yeast when present in dough, it will become unfit for eating or for use. Since formation of fungus takes place in dough, so it gives a foul smell.