I have been using a stainless spoon at the end of the boil to stir up a whirlpool and accelerate cooling without any noticeable issues (I used to just use the IC in a similar manner by swirling it). It isn't getting real splashy, either way, but it gets 10 gallons down below 100F fairly quickly; from there I just wait it out until 56F, rack to fermenter and aerate with a sanitized two blade aerator using a cordless drill. The only time I have tasted anything like that described was with an Alt that I let sit long in primary and jostled around too much moving to a bottling bucket and then into bottles. Maybe it was HSA, but I don't think so...+1. I have always stirred with a spoon while cooling with my IC to shorten cooling time. Never to a froth, but very steadily. My only two oxidized batches in 20 years could be traced to definite post-fermentation issues. One, where my daughter knocked off an airlock from a fermenter (never good), and the other from accidental splashing at kegging.