Re: Fermented Butter - The Serialis Layered head killer

I get that only cow milk has this bacteria.

What happens when you ferment butter is that the natural bacteria that would normally make yoghurt die out quickly since no lactose is available. The bacteria we want can use either lactose of fat, so one the competition is gone it grows.
Same reason why cheese containing it must be aged for 5 years. The lactose eating critters die out and allow it to spread leaving behind a very sharp taste...

There is one more way and that can be harvested after a vulcanic erruption on Islands with a sea vent. Iceland, Hawaii etc. but only stays viable for 5 years in the ash.