Kefir is a fermented food rich in yeast and probiotics, or healthy bacteria, that aid digestion. Kefir is typically made by adding kefir grains to an open jar of milk, often raw goat or cow's milk, and allowing the milk to sit at room temperature for 24 hours. Afterward, the thin, yogurt-like solid can be consumed while the grains are used to produce more kefir. Kefir grains can be stored for short periods of time when not being used to actively produce kefir.
Clean a glass jar thoroughly with warm water to remove any acidic residue such as tomato sauce. Dry the jar.
Place the kefir grains inside the jar, making sure they don't go all the way to the top. If they do, use multiple jars.
Pour enough milk over kefir grains to cover them completely. Screw the lid onto the jar.
Place the jar in the refrigerator for up to two weeks at 40 degrees F, according to the Kefir Yoghurt for Life website. If you're storing the kefir grains longer, make sure to change the milk at least once every two weeks.
Boil water in a large stockpot. Remove the pot from the burner and allow the water to cool completely.
Place a colander in the sink and put the kefir grains inside. Pour the cool water over the kefir grains to rinse thoroughly.
Lay a clean, cool towel made from terrycloth or another absorbent cotton fiber on the counter and place the rinsed kefir grains on top. Pat the grains dry with another clean towel, making sure to remove all moisture.
Place the kefir grains in clean glass jars or freezer-safe, zipper-sealed plastic bags. Add enough dry milk powder to cover the kefir grains completely, then seal the container and stick it in the freezer for up to two months.