Reader Thames asked me to comment on kefir, which is a yogurt beverage that originated in the Caucasus region (essentially the dividing point between Europe and Asia, roughly the area of extreme southern Russia, Georgia and Azerbaijan). That part of the world is what you might call a hotbed of milk fermentation, and brother do those people ever get into it. They’ll ferment the milk of cows, sheep, goats, you name it. Kefir can be made from any of them.
The thing that makes kefir different is that it’s fermented from “grains”, little semi-solid, bud-like structures that look like clumps of tapioca, but which are actually amazingly complex colonies of yeasts and bacteria combined with proteins, fats and starches. Add them to a quantity of milk and the result is a beverage that’s tangy but also alcoholic and, interestingly, carbonated. These characteristics reflect the by-products of the various microbes, those being acid, alcohol and CO2. Oh, and more kefir grains, which are handy for culturing more kefir.
Here I should note that most of the kefirs that are available commercially have no alcohol in them, though most do have at least a little carbonated “bubble”. Usually the ones that you find for sale in stores are also sweetened and/or flavored with fruit. If you’re curious about yogurt drinks, kefir is a good place to start. You can make your own by ordering the grains themselves through the mail.