I've enjoyed kefir for a few years now. For those who aren't familiar, it's a fermented dairy beverage with a consistency somewhere between milk and greek yogurt, though with greater probiotic cultures. The most popular brand is Lifeway, but after producing my own I've come to realize that commercial brands really have little value by comparison.
I've been culturing whole milk using kefir grains for almost four months, and it's much better. It takes some trial and error to get the process down, plus the smell is similar to yeast while the taste is sour and tart, but it's easy to mask and I've become accustomed to it anyway.
This is really getting me interested in the science of fermentation. I've been incorporating miso and sauerkraut into my meals lately as well. I'd like to make a vegan kefir using hemp milk or almond as a substrate, but I don't understand enough to ensure the bacteria would have a proper food source.