My mum gave a me kefir culture one summer, and after just a week I got to enjoy two little serves of homemade 'yogurt' with muesli. Did not get sick after. I call it a win.

The kefir process is less involved than kombucha, but your fermenting jar will need more frequent tending when the weather is warm.

A kefir culture looks like little cauliflower florets. They're a kind of SCOBY, bunch of yeasts and bacteria just hanging out. I got a culture that was wet and already working, but if you buy them from a store, they may come dry and require 'activation' (basically soaking them in milk until they're soggy and plump). I added full cream cow's milk and my kefir got to work.

It takes a little farting around to figure out how much milk to use and how long to leave it for, but a reasonable guess worked well enough for me. Again, the first few days saw me checking a few times a day. The pantry smells odd, with both kefir and kombucha fermenting together, but not unpleasant. Sour and clean.