Have you ever let coffee sit on the hot plate for too long and it develops that awful acrid flavor? I was wondering if this was somehow related to the roasted nature of the coffee. If so I wonder if similar flavor compounds would form from boiling beer with lots of roasted malt for to long. Any thoughts?
It is unlikely that a long boil will cause this problem. It could be the amount of roasted grains used or perhaps the water chemistry (if your pH is already low, the addition of roasted grains would take it out of range on the low end).