What are putrefaction and fermentation ?

Explanation

The process of anaerobic break down of protein by microbes is called putrefaction . It results in the production of its smelling gas `(H_2 S)` , simpler compounds and other gases like `NH_(3) , CO_(2) , H_(2)` and organic acid .
The process by which respiratory substrate is incompletely oxidised in absence of oxygen to form various organic compounds like lactic acid , ethyl alcohol etc . , with the release of partial amount of energy is called fermentation .