I believe the yeast is the top layer. At least it is in the secondary.
But, I just pour the whole bunch into the starter. All that gunk didn't hurt the last beer. And the last batch had 10 times as much total. So the second batch will have 11 times as much. Big hoo-hoo.
Decanting is just dumping beer. It doesn't do anything about infections, which is the most critical thing. Any infections will be all through it.
So far, I've had more experience thinking than I've had brewing....you don't think they are mutually exclusive, do you?
72 batches so far,
48 wine, mostly Loquat, peach, plum, prickly pear
23 beers and ciders
1 Tequila, from a prickly pear wine experiment that didn't work. I call it "Prickly Heat"