So under most brewing conditions a nonzero amount of this microbe survive, but that count is 3 orders of magnitude lower what might be termed a “therapeutic dose?”

What even is a good experimental design for probiotic tea? Brew -> agitate in hydrochloric acid & digestive enzymes for X minutes -> mix with billions of existing gut microbes (that may kill this microbe or out-compete it for resources) and incubate at body temperature -> count the number of new colonies of this particular microbe?