Wheat dough if left in the open, after a few days, starts to emit a foul smell and becomes unfit for use

Wheat dough if left in the open, after a few days, starts to emit a foul smell and becomes unfit for use. Give reason.

Answer:
Carbohydrates in wheat dough encourage growth of yeast and other sapfophytic fungi which break down carbohydrates, and emit a foul smell.