A fermented drink made from milk (similar in some ways to yogurt) and kefir grains, genuine kefir is full of natural probiotics and calcium. Like yogurt, it was made with a “starter,” in this case bacterial yeast. Kefir grains are quite complex and combine yeast with lactic acid bacteria, protein, sugar and lipids. The lactobacillus bacteria are always present even though different batches of kefir may be different to one another. Generally it is fermented overnight and can be slightly alcoholic.