I tend to get kind of an ashy flavor in roasted beers sometimes, I always wonder what causes that. Could it be the malt? pH?
Most often pH IMO. You can mash a stout or porter at 5.3 and find the roast character harsh or acrid, but mash the exact same beer at 5.5-5.6 pH and find the roast much mellower and enjoyable. The high acidity of black malts gets softened enough to be pleasant at the higher pH. Try it sometime !
Nice: pH I was going to talk about next: 5.5 sounds like a good target. Water wise what's good Sulfate/Chloride levels for a stout?
I think I'll brew two beers, a Guinness one and one with the Caraffa III + Oats that I'll age on cocoa (maybe coffee too) in a hope to get a smooth chocolate flavor.
I like to start with Black Balanced or Black Malty in Brunwater and make subtle changes on following batches if need be. Both sound great !