A big thanks again to TJ at Commonplace Coffee ... he gave me a quart of cold-pressed Sumatran Mandheling coffee extract to add to the porter. I brought it up to boiling, then quick-cooled before adding to the secondary fermenter. Going to give it a couple of more weeks before bottling. Gotta get it ready for Febtoberfest!
Edit: In answer to Eli's question in comment 1: Yep, I boiled it last time, too. You're right in that boiled coffee can be harsh, but the difference here (at least I think it is) is that boiling/hot water was not used to extract anything from the beans, which will give that bitterness. Rather, the coffee was extracted using cold water, then the extract was brought to a boil. I suspect that if I let it boil for a while, the "cooking" reactions would impart harsh flavors, but it was just to do a quick sanitize and I cooled it down immediately. Only time will tell if this batch comes out as nice as the first one!
Edit: Adam, check out Toddy Coffee; this is the little device that my buddy TJ uses to make cold extracts. They use it for making really good iced coffee in the summer. It is indeed smooth!