Diacetyl in some bottles but not in others. Why?

[Beerbeque]

Most of my bottled ales taste fine but sometimes I taste diacetyl in some of the bottles. I can't figure it out. Why do only a few bottles per batch have this fault? any ideas?

 

[TipsyDragon]

they probably all have it and just the few have more. my guess is you don't ferment warm enough or long enough. is posable that during the fermentation of the priming sugar is leaving the diacetyl.

 

[Yooper]

Very low levels of an infection (I believe it's pedio) can cause a diacetyl flavor. I've tasted it in tap beers in bars without proper lines cleaning. I wonder if some of the bottles have a very low level of infection?

 

[samc]

I would agree with some infection as it could be some of your bottles are not as clean/sanitized as the others. Can you do a batch with all new sanitzed bottles?