According to my beer kit instructions adding oxygen to the beer must be avoided. However I've read that sometimes people will airate the beer. At what stage in the brewing process does this happen in? What does airating do?
Avoid aerating when the wort is still hot--there's a lot of evidence that hotside aeration (HSA) isn't a major problem unless you really overdo it, but there's no real reason to go out of your way to aerate hot wort either.