most likely it is proteins that coagulate out of the solution when the
hot beer (wort) cools quickly along with little bits of hops that
aren't caught in the pre-filter before entering the heat exchanger.
They probably started getting caught in the channels of the heat
exchanger but I didn't notice until liquid got caught in there as
well so I could hear it when I shake it. I've tried boiling in
trisodium phosphate, soaking in oxyclean, acid-based cleanser, bleach,
turning a pressure washer on it, and baking in the oven at 400 degrees
for an hour. Nothing can seem to get these deposits out....so I
thought to try incinerating them.