Add the kefir grains and milk to a glass jar. Stir gently using a wooden spoon.
Cover the jar with cheesecloth secured with a rubber band or string and allow to ferment at room temperature (but out of direct sunlight) for 12 to 48 hours.
You can taste the kefir to see whether it has properly fermented, or watch for the whey (a clear yellowish liquid) to separate at the bottom of the jar. You may have small pockets of whey throughout the kefir.
Pour the kefir through a small fine-mesh strainer into another clean jar, collecting the kefir grains in the strainer for use in another batch.
Chill the kefir, covered, for the best taste results. Store in the refrigerator for up to 2 weeks.
Notes
Use 1 tablespoon of kefir grains for each 1 cup of milk, recipe can be doubled/tripled, etc.