It's very rare that food doesn't get digested in time and then rots in your stomach but it is possible for food to rot inside your stomach if the food isn't digested properly.
Some people have digestion issues which may cause the food to stay in your stomach longer than it should which can then lead to the food rotting and growing bacteria.
Then you would likely throw it up if it did go bad in your stomach.
The food that rots in your stomach is usually caused by complications of gastroparesis which causes the food to stay inside your stomach longer than it's supposed too which then causes it to rot.