In a nutshell, fermentation is one of the most ancient methods of food preservation. It involves breaking down foods by using living microorganisms, such as enzymes. Fermented foods are rich in friendly bacteria which convert starches and sugars into lactic acid and acetic acid.
Fermented foods also aid in the colonization of other beneficial bacteria that inhibit the overgrowth of unfriendly microorganisms, such as candida. They are easy to digest and bring a rich supply of enzymes into the body. The are a superb food for the elderly. That's another story --- about why some elderly people no longer have the stomach and intestine enzymes they need. Maybe we'll talk about that another day.
Miso, tamari, sauerkraut, apple cider vinegar, kim chee, yogurt, Rejuvelac, kombucha, and kefir are all fermented products, and there are many others. All are incrediblly beneficial to the digestive system, and should be eaten often, young or old. And the best way to get them is to prepare them yourself. I do buy apple cider vinegar, but make sure that it is raw, so that those precious enzymes are still in tact.
So, read up on the subject, or come to Clover's on Thursday for the Fermented Foods--Nature's Best Probiotic discussion.