Hi FF, Yes, it does mutate. I use Natren yogurt starter and they recommend that you use fresh starter culture everytime you make it. If I use the yogurt as a starter culture more than 3 or 4 times it weakens. However, I use raw goat's milk and if I want a firm yogurt I find I have to use fresh starter every time.
I have never heard of LB17. I am going to try it Thank You....