"Kefir, however, typically contains three times the amount of probiotic cultures than yogurt. To make kefir, milk is fermented with a mixture of 10 to 20 different types of probiotic bacteria and yeasts; most yogurts are made using only a few. Liberté organic kefir, for instance, delivers 40 billion probiotic organisms per half cup, while most probiotic yogurts contain roughly one billion per serving."
What’s the difference between yogurt and kefir? - The Globe and Mail