Passing wind is entirely natural, but can be an annoying and sometimes painful process, caused by bacteria in our gut. In a process of fermentation which releases gas and heat, colonic bacteria break down indigestible fibre and starches which haven’t been absorbed in the small intestine. This gas is usually made up of carbon dioxide, oxygen, nitrogen, hydrogen and methane. Certain foods can lead to the production of gases containing Sulphur, too. Most of this gas is absorbed into your blood stream, and the rest is released as flatulence.