Hot side Aeration?

Not sure if that's even the term I'm looking for, but here's my question: Does splashing your wort (mash runnings) around pre-boil lead to off-flavors?

The last two of my batches had some astringency to them, and a friend pointed out that this might be the cause. I have a very primitive all-grain set up, where I drain my runnings rapidly (after a slow vorlauf) into a bucket, then pick up the whole bucket and pour it not-so-gently into the kettle. Is this aerating it, and contributing to off-flavors? I was under the impression that this is fine because boiling takes care of everything. Thoughts?

No, once you boil the O2 is removed from the beer through the boil process. Astringency has more to do with the temperature of mash, PH levels and the amount of darker specialty grains in the grist

http://www.kroc.org/Links/TroubleshootingGuide.htm
http://www.howtobrew.com/section4/chapter21-2.html