[HoosierBrew]

  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 !

On these beers, the pH must be getting too low on me. I usually add some baking soda to raise the pH, but maybe not enough. Wouldn't Guinness be ashy then since they mash low? Or is the function of their sour mashing process the differing factor there? Definitely don't care for that ashy flavor I get sometimes. Ick.

If I'm correct, Guinness steeps the roasted barley separately (with nothing added to raise pH) producing a sort of tart wort, which they then blend with the main mash of pale malt and flaked barley, which is pH controlled. I guess they hit the right ratio of tart black wort to main wort since it tastes so good. I agree I don't like the ashy, acrid character at all. I dumped a batch of stout a few years back that had more ashy than I wanted. All I know is everything mashed together @ 5.5-5.6 pH makes a pretty killer porter or stout. I need to brew one this fall !

[beersk]

I don't recall ever getting that flavor when I used to add the roasted malts at the end of the mash. Maybe I'll try that again sometime. I rarely brew dark beers so it's not something I've done a lot of experimenting with other than adding those dark malts at the end of the mash a few years back.