Old thread, I know, but.... Since I worked at Stroh's on the Keg Line and in packaging on a filler, and in brewing I thought I would chime in and help out with your questions. We did indeed use Porterine. It is just a dark carmel coloring and from what I was told, it was specially made for the proteins to mingle nicely with our regular Stroh's. This I learned in my short stint in brewing. I was summer help, a college program, so, I wasn't privy to their serious secrets, but since I was charged with weighing up ingredients I learned about Porterine.
I worked in packaging and got to know the Q&A guys, they would stop by each line, we had 8 lines in the Winston Salem Stroh's Brewery, they would gather samples just about hourly for testing. This is where I heard about Porterine's special properties pertaining to proteins. I was interested in possibly starting my own Brewery one day, So, I tried to soak up as much info as possible.
I worked on the keg line the final year I worked for Stroh's. We only ran the Keg line on thursday nights. Kegged Stroh Products weren't that popular in the Southeast which is what we really produced our beer for. The local markets of TN, NC, VA, MD, D.C., SC, GA and AL. So, we ran one night, typically 8 hours a week would take care of our Keg needs. Small run time wasn't it?? While on the Keg Line, we did run Bock and Stroh Dark. I was tasked with measuring out the Porterine to add to each keg in the run. Usually no more than 10-15 kegs.
So, there you have it.