Place about 2 teaspoons of kefir grains into a clean glass jar.

Add about 3 cups of fresh milk, leaving about 1 inch of space at the top.

Place a plastic lid on loosely — don't tighten it.

Set the jar in a warm spot, out of direct sunlight, for about 24 hours. It's ready when it smells fermented, looks slightly thickened, and has small bubbles.

Tighten the lid and gently shake.

Strain the kefir into a clean jar using a stainless steel or plastic strainer. The grains stay in the strainer for your next batch.

Optional second fermentation: Add fruit to the strained kefir, seal tightly, and let it sit on the counter for 2–5 hours. Then refrigerate.

Next batch: Don't rinse the grains. Place them into a clean jar, add fresh milk, cover loosely, and repeat.