Question

when a wheat dough left in open it starts emitting a foul smell why?

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.

Answer 2

this occurs since rancidity takes place