How to Ferment Milk

by Genevieve Van Wyden

Boy drinking a glass of milk.

Dave & Les Jacobs/Blend Images/Getty Images

Kefir grains are the starter culture used to ferment fresh milk and create a sweet or sour kefir. When kefir grains are used to ferment milk, the process is similar to making yogurt. Kefir, or fermented milk, contains more probiotic cultures than yogurt, according to the KefirOnline website. It is possible to ferment fresh milk at home, but you need to be very careful to keep your hands and equipment clean. As you store and reuse the starter culture, its quantity grows just a little.

Pour the kefir culture into the glass container.

Pour the fresh milk into the container until it is about two-thirds full. Cover the jar with a clean lid or cloth.

Leave the milk-kefir culture mixture on the counter for 24 hours. If you leave it out for only 12 hours, it will be thinner and have a sweeter taste. If you leave it out for closer to 48 hours, it will be thicker and taste more sour.

Mix the liquid kefir and milk curds that have formed in the jar with a wooden or plastic spoon.

Place a non-metallic sieve on top of a second jar, and pour the kefir into it, allowing the liquid to seep into the jar.

Place the kefir grains in the sieve into a clean, small jar with a lid. Do not wash the grains. Save them for the next batch of kefir.


  • As the kefir is fermenting the fresh milk, a jelly forms around the grains. Called “kefiran,” this jelly helps add to the thickness of the kefir you make.

    Ensure that everything you use to make kefir is very clean before you start a new batch.

    A jar with a lid and rubber gasket is ideal for storing kefir.

    Temperature impacts the speed at which kefir ferments. In warmer places , kefir ferments more quickly.

    The kefir grain is made up of different kinds of bacteria and yeasts that take the shape of cauliflower. The grains are held together with fats, proteins and sugars. All of these products in the kefir grain work together to ferment milk. The bacteria in kefir grain are live probiotic cultures.

Photo Credits

  • Dave & Les Jacobs/Blend Images/Getty Images

About the Author

Genevieve Van Wyden began writing in 2007. She has written for “Tu Revista Latina” and owns three blogs. She has worked as a CPS social worker, gaining experience in the mental-health system. Van Wyden earned her Bachelor of Arts in journalism from New Mexico State University in 2006.