Kombucha can have very high amounts of vitamin B12 (e.g. https://www.reddit.com/r/mildlyinteresting/comments/65wjep/this_kombucha_has_a_ridiculous_amount_of_b12/).
Where does the vitamin B12 come from? From which process?
When I make my own Kombucha, how can I tune the amount of B12? Which ingredients should be in there / to what should I pay attention?
