Peoples taste

[AnthonyB]

OP also indicated that it happened 4 times, and that at least one of those times was thought to be from old hops. Either way, 4 occurrences of a pedio infected draft line is completely possible in my mind.

But since you don't think so, what else could it be?

More likely something in process at the brewery. Perhaps some remaining acetolactic acid is being oxidized into diacetyl via improperly purged kegs or through a lose hose connection somewhere. If a forced test on a purportedly defective keg was negative, then I would start looking more closely at the different customers' lines who are reporting the beer.

[Bankbrewer]

I had diacetyl coming out of a freshly tapped keg on my home kegerator, I was afraid it was the beer. Then I bought some new tap line since it was over a year old and voila, no more diacetyl.

Tap lines at bars now scare me.
I've talked to our distributor and he says they clean every line twice a month, but if brands get swapped during that time they can't control that, all we can do is continue to educate the draft line operators as to how our product is supposed to taste and proper draft techniques to help them succeed.


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[campbell.brian]

Test for VDK and start quantifying with a lab number...

http://coastalsciencelabs.com/brewing-and-winemaking-services.html

Then try and correlate that with reported instances of the issue... another thing you might do is try and specificaly track down a person who does taste whatever is going on, or seek out an outside, 3rd party taster who isn't familiar with the beer and get a blind tasting from them.

More likely something in process at the brewery. Perhaps some remaining acetolactic acid is being oxidized into diacetyl via improperly purged kegs or through a lose hose connection somewhere. If a forced test on a purportedly defective keg was negative, then I would start looking more closely at the different customers' lines who are reporting the beer.

The decarboxylation of acetolactate into diacetyl is spontaneous. Rather than trying to prevent it, most brewers try and force the reaction into diacetyl by warming the beer after fermentation to ~ 60°F. The yeast will subsequently absorb the diacetyl during maturation or lagering. If you lager without this step, acetolactate remains in the packaged beer and diacetyl will form once the beer has left the brewery. Testing for VDKs would be the best option here.

Unless you can test for VDKs in the brewery, torture test some of your packaged beer. Try warming up some of the beer to 60-64°F for a day or two, then cooling and tasting. If buttery flavors develop, it's most likely VDKs (acetolactate).