Preface: I do not want to start a discussion about whether to soak or not soak beans. There are numerous discussions on the 'net and on CH about that. I soak (see below). It works for me.
I conquered my fear of beans. I soak my beans (see above, please I do not want to discuss this), drain, rinse, and cook them until soft in a 300F oven. But I hate to waste food...and throwing away the bean cooking water always struck me as just that - a waste of good ingredients. So I save it. I use it to I reheat my beans with other items. Bad bugs?...Eh, all I can say is, here I am. And I think us moderns overreact to bug stuff and I always boil things that I've saved for at least 30 seconds.
So here's my question. My last batch of bean water lasted for several days. Yesterday, when I took it out. I noticed it had separated into two layers: a watery top layer and a thick sludgy bottom layer. Sludgy makes it sound disgusting but it wasn't. It was just a thick paste. I used it to heat up the last of my bean batch, with some cooked hominy, and it was delish, in fact, it thickened the combination very nicely.
What was this? Bean starch? These are black turtle beans, by the way.