I keep reading that there is no vegan source of B12. But two days ago in the Science Times, an item mentioned that there is some B12 in tofu and in soy milk. So is there B12 in soy beans? And where do cows get their B12, BTW?
B12 in animal products comes from the bacteria they eat: Vitamin B12 - Wikipedia
There’s definitely vegan B12 (bacteria are not animals):
https://www.amazon.com/s?rh=i%3Aaps%2Cp_85%3A1&keywords=vegan+b12
Or check your local co-op/whole foods/trader joe’s/upscale white grocery store.
I doubt there’s meaningful amounts of B12 in regular soy milk unless it were deliberately fortified (which it may be, targeting vegetarians who don’t get it from meat). But that’s the same as just taking a B12 supplement.
If you’re worried about vegetarian/vegan diet issues (not sure from your post), I highly recommend the book “Becoming Vegan”:
I’m a vegetarian who eats eggs and dairy, but I love tempeh.
As the Wiki article points out, this unfortunately isn’t a reliable source of B12. Sometimes it’s there, sometimes not, but unless it’s deliberately fortified, it’s an accidental inclusion in the production method and not controlled for quality or quantity.
It’s fine if you’re vegetarian because you’ll probably get it from eggs and dairy. As a long-term vegan, it’s important to supplement this properly and not just rely on occasional intake from accidental inclusions 
Well, according to the oldest Plant or Animal Kingdoms, they are animals.
But yes, the various Kingdoms have been changed quite a few times, and they are now in their own Kingdom, and so are Protozoa, Chromista & Fungi.
However, what makes you think that vegans keep up with the latest changes in cladistic classification for the dietary choices?
One definition is eating only vegetables. (VEGan)
Yeah, I admit the kingdom reclassification excuse is sort of a retcon or copout. Though, more often, that ambiguity is around fungi (mushrooms, kombucha, beer).
I think the real reasons are just more… pragmatic:
- Most vegans are more worried about the perception of pain/suffering more than taxonomy. (I wonder what we’ll do once we better understand the distress response in plants.) Many are specifically anti-factory-farming in particular, and while cultured bacteria are certainly factory farmed… the hope is that they’re not suffering much during the process. One would presume??
- Everything has bacteria (maybe not enough of the B12-forming variety) and a diet without them would be starvation
- We’ve been historically terrible at defining “vegetable” (fruits? mushrooms? seaweed? yeast?)
Which might be why quite a few vegans I know define vegan as “no food from animal sources” which, under current taxonomy, means bacteria are OK. As are fungi, and you don’t have to argue about whether a tomato is a vegetable or a fruit.
Yeah, exactly. That’s also useful in differentiating between vegetarians (who still consume animal-produced substances, just not their flesh.)
But there’s no such thing as pure veganism anyway. Many plants depend on animals for soil tillage and fertilization and pest control, not to mention CO2 production. Many animals (insects, mice) are killed in robotic farm harvests. Many plants eat animals, usually after they’re dead.
At the end of the day, it’s not necessarily about laboratory-grade purity. Even a 95% decrease in animal food is a lot. Even Meatless Mondays is more than most people would ever attempt. But there’s a also a discussion to be had about how many vegans it’d take to actually decrease animal agriculture rather than just increase spoilage…