How do you aerate

[Barley Water]

I aerate by shooting pure O2 into the cooled wort for about a minute through an airstone. I almost always make a starter on my stir plate (except when I make heffe, I want to stress the yeast on purpose so I just pitch straight from the vial). Of course, if I am doing lagers, the starter is a hell of a lot bigger than I would do for ales but I do want healthy yeast going in.

I would submit that if the yeast is dropping out before finishing the job, there is something else going on. You should not have to add O2 in the middle of the fermentation, especially not for normal gravity ales. I use WLP02 quite a lot and that yeast is extremely floculent. If any strain would fall out of suspension too quickly, that would be the one and I have never had any problems. In the dark days before I figured out that lagers require a massive starter, I had all sorts of problems with under attenuated lagers (and I also got excessive esthers and phenols). If you are having the yeast falling out before finishing the job, my first quess is that you are under pitching. It could be that the yeast you are getting is old and the viable cell count in the packages is lower than it should be. The other problem you might be experiencing is too low a fermentation temperature. Here in Texas, we rarely have that problem but on your side of the pond it may be an issue.