Despite my heroic efforts to reduce exposure to air when transferring hoppy beers from FV to keg (and keg to keg), I was recently upset to find out that an otherwise very good hoppy american session ale was starting to show signs of oxidation - short finish, cardboard taste. This was in a keg. I read up on this problem, which I observe in hoppy beers more than other styles. In the Beersmith podcast with charlie bamforth on beer stability
CB states that you can get rid of this flaw with yeast. So i decided to put it to the test. I made a small starter using mauribrew dried yeast and pitched into the keg when it was at high krauesen. Have left it for a week or so now. I tasted it last night and the oxidation flavour (trans 2 nonal I believe) has gone!
There is however a hint of diacetyl, which I hope will disappear with time. It is certainly nicer than the "untreated" beer and has gone from being a tipper into a drinker.
In the podcast CB also talks about using sodium metabisulphite as a precautionary measure to improve stability and reduce oxidation. I think I will try this for a subsequent hoppy style as I am quite sensitive to oxidised flavour in hoppy beers and I don't like tipping beer. Not too worried about rheinheitsgebot..
Anyway, if you encounter this issue, adding yeast in the keg appears to resolve it, so worth a go..