Fermented foods are foods that have been exposed to beneficial bacteria and/or yeasts, which eat up carbohydrates and produce a variety of organic acids in their place. This process results in novel flavors, a little tart, often complex and interesting.
In some fermented foods, the bacteria have already died off before we eat them. For example, chocolate and coffee. In others, the bacteria are still alive when they get to us. For example yogurt and sauerkraut. These latter are especially good for us, because some of the healthy bacteria can move into our gut and continue living there. You’ll notice with living cultures, the flavors strengthen and deepen.