Boiling kills the bacteria only. Kefir or yogurt bacteria consume the milk sugar.

jhan

You boil milk (it's called skalding your milk, like in the old days) to remove bacteria that will always get in your milk, because they can't stop even small pieces of feces getting into it. These small pieces then get mixed in with a huge batch and they get stirred up and the bacteria culture grows.

Hulda Clark talks about it in her book "The Cure to All Diseases". It's a major problem with all milk products.

I myself choose not to have milk products, they are too mucus forming anyway.