Where'd that Diacetyl come from?

I just tasted a brew that I tasted out of the fermenter and it had no buttery taste at all, but now after 2 wks in the bottle it is buttered popcorn... this has never happened to me before and I'm not sure what happened? Could, diacetyl have formed because I had the primed bottles at 68 for a while before bringing them up to 72? Could it have come from the priming?

Thanks!

If your brew had completly finished fermentation with no diacetyl, then you should get none from the priming sugar addition.
Could be you have had an infection that caused the diacetyl in the bottles.
Let it age for a month or so and try it again.

It is possible, I suppose, that diacetyl would be created when fermenting the priming sugars. It should be cleared up quite quickly.

Cool, I'll let it sit, has only been 2 wks in the bottle - I just usually start tasting at one week and in 20 or so batches have never even tasted it then... I'll check next weekend.

Keep in mind that some yeasts produce more diacetyl than others. Looking at your footer, is this the ESB you are talking about? It's an accepted aroma/flavor for the likes of an ESB.

I recall reading in New Brewing Lager Beer that diacetyl can also be produced by the beer getting oxidized post primary fermentation... and that this can be irreversible.

I was just reading the same thing on BYO when looking up some info on Lagers (not that this is a lager being discussed here, but the info is still good.)

http://byo.com/component/resource/article/870-how-can-i-minimize-diacetyl-in-my-lagers

Specifically:

BYO said:

I think what is happening is that you are picking up some oxygen during your racking step and the oxygen converts diacetyl precursor (i.e. alpha acetolactate) in the green beer into diacetyl during lagering.

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This is an American Amber that I have brewed before - I use Wyeast American Ale yeast (1056). This was fermented at about 74 which is warmer than ideal but it was before I started using the swamp cooler and 2 degrees above the high for the yeast is not uncommon and if anything I'd have figured I would have esters or fusals instead of acetyl's. That's why I was wondering if it could have come from the priming...

Oh crap, my wife was stirring this while I put it in the bottling bucket - usually I put the priming sugar in and fill the bucket up on top of it stirring very gently... I never have a helper... well she stirred the whole time I was filling the bottling bucket, gently but constantly, I wonder if I oxygenated the friggin' precursor! Crap... will bottle conditioning fix this ya think or am I buttered?

Netflyer said:

Oh crap, my wife was stirring this while I put it in the bottling bucket - usually I put the priming sugar in and fill the bucket up on top of it stirring very gently... I never have a helper... well she stirred the whole time I was filling the bottling bucket, gently but constantly, I wonder if I oxygenated the friggin' precursor! Crap... will bottle conditioning fix this ya think or am I buttered?

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I think it can to some extent. If krausening can reduce diacetyl (it can), then the yeast activity from fermenting priming sugar should result in some diacetyl metabolism, but perhaps not all. So, I wouldn't have high expectations, but there is some hope. Give it time and let us know.

I think the moral here may be: Don't let yer assistant stir your precious, just out of the primary for 21ish days, beer as you transfer it to the bottling bucket. Blasted O2... bah...