How is methane produced?

Liam Sinclair, Professor of Animal Science, says: "Methane is produced in the first stomach of the cow which we call the rumen. In there we find billions of microorganisms that ferment the food that goes in. As a consequence, the cow produces methane which she burps out. This is part of the natural digestive process and it's something that cows have evolved over hundreds of thousands of years."