Though there are reported cases of bad breath emanating from stomach, such occurrences are very rare. The esophageal tube, which connects the stomach with your mouth, is not an always open tube, but is closed most of the times.

Every chunk of food you ingest moves down so slowly down to the stomach, just like a snakes eating frog. We often belch sometimes with every food chunk, when a little bubble of air moves from the stomach to the mouth.

Whenever, there is a belching incident, some people may emit foul smelling gas from their stomach. However, though it may sound true, bad odor from your stomach is a rare occurrence. Thus it seems the stomach is probably the last place to look for foul odors and gases.