Thanks for the replies, everyone.www.yeastcalculator.com
says I need 170 billion cells for a 3.5 gallon 1.052 hybrid ferment. Using Kai Troester's stir plate model, a 1 liter starter is predicted to give about 222 billion cells. This doesn't sound like a significant overpitch, especially when Jamil's model only predicts 187 billion cells for a 1L starter.
I'm wondering if it's an acetobacter infection, although I've never had one before and my kitchen is damn near spotless with no fruit flies to be found. Everything gets a soak in PBW followed by a hot water rinse and then a soak in star-san before I rack from kettle to fermenter.
I'm wondering if too much kettle trub made it into the fermenter? I've been a bit lazy about that lately, racking everything except the thick sludge at the very bottom. I've done this on several batches now without issue, but maybe my luck has run out.
I'll give the beer another week in the fermenter and see what happens. After that I'll do a 180 F hot water sterilization of my equipment and try another brew.