Kefir is a fermented milk drink made with kefir “grains”, a yeast/bacterial starter. One tablespoon of grains makes a cup of kefir that you can drink, serve with your muesli, add to many dishes. Your grains will multiply so you can make more and more kefir. You can even eat the kefir grains.
Products made wtih kefir are lactose free and don’t encourage the growth of yeast, which can cause allergic reactions in some individuals. You can even use kefir to make a cream cheese-like product.