When you eat too much, eat when you feel stressed, or eat when food is poorly combined, the food sits in the small intestine and putrefies. Bacteria and yeast feed on stagnant food and release gas in the process.
You can think of kefir as a rich microbial soup. It contains both bacteria and yeast. While the word “yeast” may scare people, beneficial yeast can be just as valuable as beneficial bacteria in healing the inner ecosystem.