If I am worried about diacetyl and I already cold crashed to 50 and transferred to keg, is there anything I can do?
Yeast is just about the only thing that can remove diacetyl from beer. That said, it may not always be a bad thing. Good info here: http://www.byo.com/stories/techniques/article/indices/19-brewing-tips/2437-diacetyl-techniques What kind of beer are you brewing and what makes you think you have a higher-than-desirable level of it?
I had a diacetyl problem earlier this year with a classic American pils. I waited for the yeast to clean up the diacetyl and it never did. I was able to get rid of the diacetyl by making a simple starter with some new yeast and pitching it into the beer after the yeast reached a vigorous fermentation. I was only able to get my hands on some Nottingham dry ale yeast, I don't remember the exact timing of events but I waited several weeks before trying the beer. It did the trick.
^^^ what they said ^^^ I recently brewed a German Pilsner that a bit of diacetyl. I drew about a liter of a Cream Ale that was at high krausen and added it to the keg. That beer used US-05, so I had to fine it when it was done, but it came out just fine.
OP - This is the classic step if you are at that point. Called Krauesening(SP) in the brewing literature. The yeast will use the diacetyl for an energy source once all of the sugars are gone, and this technique can also be used to carbonate the beer. OP - the name nervousbrewer must be factual.
