Putrefy
/ˈpjuːtrɪfaɪ/
Definition 1 of 2
Pro Tip 1/3Strong Odor
Putrefy emphasizes a bad smell from decay, more than just rotting alone. 
Despite cleaning, the smell of putrefy remained.
Pro Tip 2/3Advanced Decay
Use 'putrefy' to describe something past initial stages of decay, advanced decomposition. 
In the summer heat, the roadkill began to putrefy rapidly.
Pro Tip 3/3Negative Tone
The term 'putrefy' carries a negative connotation, indicating disgust. 
The abandoned fridge was filled with food that had started to putrefy.