I'm fermenting a small batch of Irish Red, and after the first couple of days, there is a pretty substantial amount of scum at the top of the jug. Question: do I reintroduce the stuff back into the wort by tilting the jug, or just leave it alone?
Just heave it alone. It is the remains from the growth of the krausen layer. The "foamy" stuff will settle out and you will just have to soak/scrub the jug after you remove the beer but do not add it back to the finished product. Here is a picture of your batches big brother. My krausen has already started to drop but you can't tell due to the crusties on the carboy.