The differences between kefir and yogurt is in three main points:
1. Kefir contains considerably more probiotic bacteria than yogurt. While yogurt may have a maximum of 6 probiotic bacterial strains, milk kefir can contain up to 50 different probiotic bacteria. Moreover, Kefir also contains many yeasts, while yogurt doesn't contain any yeast.
2. The probiotic bacteria of yogurt are transient, meaning that they pass through the gastrointestinal tract and are then discarded. Their beneficial effects only last as long as they stay in the GI tract. Unlike yogurt, the bacteria of Kefir have the ability to colonize the gastrointestinal tract and tend to stay there much longer.
3. The probiotic bacteria of Kefir are mesophilic, which means that they coagulate (ferment) milk at regular room temperatures. On the other hand, yogurt bacteria are thermophilic, which means they need higher temperatures to thrive and ferment: about 30-35° Celsius (85-95° Fahrenheit), marking the preparation of Kefir more straightforward and accessible than yogurt.