I've been digging through the "Search" function for a few hours now, trying to get info, but I'm at an impasse.
I've gotten a husky/raw grain/ astringent? flavor on a few beers I've done recently. The obvious culprit is tannin extraction, and the most common cause of tannin extraction is sparging too hot and at too high of a pH. I've read that tannins could also be from break material in the fermenter. But I've also read that break material and trub don't affect the beer.
Here's my process: I use the Deathbrewer BIAB method, squeeze the bag, sometimes use decoctions, batch sparge, don't filter the wort going into the kettle, or into the fermenter. Sparge @ 165* and I acidify the sparge water with 88% lactic acid to make sure it's under 5.8 before sparging. Mash pH between 5.2-5.5.
I've made a lot of beer (20+ batches) with the above method without grainy flavor. I'm trying to pin down when exactly the flavor started, and I think it was about the time I bought my last bag of malt. I've made about 6 batches with malt that was milled by a maltster, instead of my 2-roller mill. The crush is finer than I get on my mill, and extract efficiency is better. I also used to use a metal colander to strain out hop particles going into the fermenter, but in the last 6 batches haven't bothered.
Going over my brewing log, the only differences between the 3 batches with the grainy flavor and the 3 batches without has been the OG, with the lower OG batches not showing the graininess, and the high OG batches showing it.
I notice a bit more fine grain going into the boiler than before, and I wonder if filtering before the boil might help. Also, I wonder if straining the hops out pre-ferment might help, maybe by catching some of the break material in the process.