Just realised I never posted properly about milk kefir. I've been making it for over a year now. I started off just using it in smoothies as it was yeasty and tasted horrible to me. But once the grains settled down they started making a really tasty drink. For information on the wonderful properties of kefir I can highly recommend this epic website. I can't think there can be any questions about kefir not addressed there somewhere!
To make kefir you just add some grains to some milk and leave them alone at room temperature. The time taken to turn the milk into kefir depends on how many grains you have, the temperature and how much milk they are in. The kefir is done when the milk starts to coagulate. You can then strain out the grains and either drink the kefir straight away, or put in a clean jar to further ripen (for more info see website linked above).