Is this the result of a poor cold break?

[Hermit]

The more I think about it, this and better control of fermenation temps are the obvious culprits.

As for the oxygen....its recommended for big beers, but I'm not sure you have to do it for the more session/ordinary beers (e.g. beers with OGs 1.040-1.060).

I do alot of beers in this OG range and just shake the fermenter before pitching yeast. Sometime I don't even do that (forget, etc). Never had a problem with attenuation. I focus more on pitching enough yeast.

Plus, you are using starters....alot of the yeast growth that requires oxygen (i.e. reproduction) goes on when you make a starter...so its possible that the oxygen you are putting into the wort via oxygenation/aeration isn't being used because the yeast are beyond that particular growth stage (for the most part). There are alot of caveats to this line of reasoning, but its as good of a guess as any...

Just my 0.02

Bottom line. He said he uses the oxygen/O2 stone for 3 to 5 minutes. I don't use this set up but everyone that does posts they use it for 60 seconds. Either way, he should back off and give big beers a second shot at 12/18 hours per Chris White's new book.