is a fermented dairy product similar in many ways to yogurt and buttermilk. It's how kefir is cultured that makes it really unique - instead of heating the milk, adding a culture, and keeping it warm as you do with yogurt, all you need are milk and milk kefir grains.
Kefir grains are not really grains at all (don't worry , gluten-free folks). These "grains" are actually tin, rubbery, knobby-looking cell structures that are home to the bacteria and yeast that ferment the kefir.
How does it work?
It's extremely simple. Add these kefir grains (anywhere from 1 tsp to 1 tbs is good) to 1 to 1 1/2 cup of milk, cover the glass, and let it sit out at room temperature for about 24 hours. During this time, the healthy bacteria and yeast in the kefir grains will ferment the milk, preventing it from spoiling while transforming it into kefir.
When done, the kefir will have thickened to the consistency of buttermilk and taste noticably tangy, like yogurt. Strain out the grains so you can use them in another batch, and the kefir is ready to drink. You'll find sources who are adamant that you should not use mental utensils when working with your kefir. My understanding is that stainless steel is acceptable, but the acidity of kefir will not do well with reactive metals such as copper, aluminum and zinc. I like to use a nylon strainer, but I don't have a problem with using stainless steel spoons.
As long as they stay healthy you can reuse kefir grains indefinitely to make batch after batch. And the best way to keep them healthy is to keep making kefir! You an make a new batch of kefir roughly every 24 hours (the temperature of your kitchen can affect the exact time) just by putting the kefir grains in a fresh cup of milk. Over time the grains will multiply and you can either discard the extra or share it with friends. You can also take a break from making kefir by putting the grains in a cup of water and store it in the fridge for a couple of days. I call this "parking" the kefir.
Why make and eat kefir?
The live bacteria and yeast found in kefir grains are friendly microorganisms that not only aid the digestive system but also help strengthen the intestines and resist the growth of harmful bacteria or pathogens. It has been suggested that kefir is an “an almost ideal probiotic dairy product.”
Kefir Vs. Yogurt
Kefir and yogurt are both fermented dairy products; therefore, this may lead some to assume that kefir and yogurt both offer the same health benefits. However, this is not the case. Kefir contains different types of beneficial bacteria than yogurt. Yogurt contains transient beneficial bacteria that keep the digestive system clean and provide food for the friendly bacteria that reside there. But kefir can actually colonize the intestinal tract, a feat that yogurt has not yet matched. Home made kefir can contain as many as 50 beneficial strains of bacteria and yeasts, while yogurt contains only 7-10.
"Kefir contains several major strains of friendly bacteria not commonly found in yogurt, Lactobacillus Caucasus, Leuconostoc, Acetobacter species, and Streptococcus species.It also contains beneficial yeasts, such as Saccharomyces kefir and Torula kefir, which dominate, control and eliminate destructive pathogenic yeasts in the body. They do so by penetrating the mucosal lining where unhealthy yeast and bacteria reside, forming a virtual SWAT team that housecleans and strengthens the intestines. Hence, the body becomes more efficient in resisting such pathogens as E. coli and intestinal parasites. Kefir’s active yeast and bacteria provide more nutritive value than yogurt by helping digest the foods that you eat and by keeping the colon environment clean and healthy. Because the curd size of kefir is smaller than yogurt, it is also easier to digest, which makes it a particularly excellent, nutritious food for babies, the elderly and people experiencing chronic fatigue and digestive disorders."
There are also water kefir grains available for people with milk allergies.