Some people may not exactly be familiar with Kefir, but this is fermented with the use of special Kefir grains. Usually, the fermentation process will take more than a minute. Buttermilk, on the other hand, comes from skim milk, which is different from Kefir, which makes use of whole milk. For buttermilk, the fermentation will take place with the use of lactic acid bacteria.
The lactic acid bacteria is called Streptococcus Lactis. There are some people who would use Kefir as a substitute for buttermilk, especially when they need to bake. There are just some special adjustments that need to be done from time to time because the consistency is sometimes too thick.