Don’t ask, don’t tell.
The missus had a good question about probiotic critters last night. She wanted to know whether when you make yogurt at home using a commercial probiotic yogurt as a starter, you grow more of those same probiotic bugs in your batch. My guess was yes, if only because everything that’s in those factory-made cups probably has to be able to thrive under the same environmental conditions. Curious, I decided to go over to the Stonyfield Farm (my go-to starter yogurt) web site to see if I could discover what kind of microbial zoo they were keeping. I found the usual suspects there (L. bulgaricus and S. thermophilus) as well as some of the more typical probiotic bugs L. acidophilus, Bifidus and L. casei. The sole suprise was a bacterium by the name of L. reuteri. This is a microbe that isn’t typically found in the guts of humans, but rather in barnyard animals like goats and pigs. The fact that it’s found in yogurt isn’t a big deal at all (in fact for Stonyfield Farm it’s a selling point), since L. bulgaricus and S. thermophilus themselves probably originated in the guts of cows. And anyway there’s evidence to show that L. reuteri offers significant benefits to humans when ingested regularly. Still, there’s something a little unsettlling about eating bacteria that are more common to the intestines of mice than of people. Like I said, when it comes to probiotic bacteria, it’s probably better not to know.
But to answer the question my feeling is that if these creatures are alive in the starter culture, they’ll be alive in a finished homemade yogurt, though whether they’ll remain in numbers that will do a body any good, I can’t say.
UPDATE: Reader Aaron suggests Liberté yogurt as a starter (if you live in North America).