The way to prepare kefir is by fermenting milk (originally dairy milk, but it’s also possible to use plant-based milk that is high in protein) with kefir grains or kefir powder starter. The fermentation process takes around 12-24 hours and it turns the sugars in the milk into lactic acid. After that, you can strain out the grains. To see detailed instructions and a video on how to make kefir with grains, check my post “How to make kefir (vegan or with dairy)”.