Fermented foods may have an ancient history but they are experiencing something of a renaissance right now. Kefir, kombucha, sauerkraut, yoghurts, pickles, kimchi - they are surging in popularity because of their health benefits as well as because they are fun projects for cooks who want to make things from scratch or preserve the bounty. Most commercially produced fermented foods in supermarkets have been pasteurised, killing off healthy bacteria in the process. But it's easy to incorporate some homemade fermented foods in your lifestyle, if you know how.