I am no expert, but if it has white on it I assume it is yeast. Like the dull whiteness you see on almost every fruit before you wash it (not store fruits). I do not think brown is yeast, though I could be wrong. Creamy white is often used as a descriptor. Not blobby brown. Oooh, a new beer name. Dibs!
Without scoping it though, you are taking a gamble no matter how you decide to use it. I usually ferment it out and see if there is anything along the way that produces something good. If I let it go a couple weeks and the first week is good, but the second week starts producing some off flavors, I go back and start isolating early with the next batch. By batch I mean starter. I don't make more than a 1L starter for building these up, and usually 250 is the biggest flask I'll break out in the beginning. I do have a scope, but I haven't gotten to use it much.
I am by no means a professional, so take what I say with a grain of salt.
I'd like to say you are making a mountain out of a mole hill, but you are asking the right things. It is just that this isn't a science most people are diving into, on our scale. There are tons of little guys like us out there doing it though; Sui Generis' 50 Meter Beer Project is good for info, the old dissertation by him was excellent yeast information. I think I saw you mention him as a source of idea, his older stuff was great:
Yeast Wrangling
Bootleg, Bison (
Tame the Yeast: How to Capture Wild Yeast for Homebrewing), to name but a few others.
On deck is my nut brown ale: Blobby Brown
