Inspired by the mall stand beverage made with orange juice, milk, and vanilla, this drink is thick and satisfying.
1. Pour milk into pint-size glass jar, and stir in kefir grains. Cover jar with several layers of cheesecloth or paper towels, and secure with rubber band.
2. Store jar at room temperature out of direct sunlight and allow kefir to ferment until thickened. (Healthy kefir grains will thicken milk in 24 hours, though this process may take as few as 12 hours in warmer temperatures, or as long as 48 hours in cooler temperatures.) Check kefir periodically to gauge thickness.
3. When mixture reaches desired thickness, strain kefir into glass, stirring gently until only kefir grains remain in strainer. (To keep kefir grains viable, stir into new batch of milk within 48 hours.)
4. Combine prepared kefir, orange juice, vanilla, and sugar in blender. Pulse to combine. Blend in ice cubes individually until as creamy and frothy as you like. Taste, and blend in more sugar to sweeten as desired.