[factory]

I recently got scoresheets back from a completion in which I entered a Light American Lager.  I sensed a slight buttery flavor to it, but my perception of diacetyl is slightly different (pick it up as a slightly rancid taste with that slickness that you can feel on your tongue).  I entered it anyway, and got it scored at a 34, 36, 38 from the judges.  All noted the butter flavor but not one of them dinged me for diacetyl. I believe that one of the judges was a National. 

All that explanation for this:  Where do buttery flavors come from other than diacetyl? The grain bill was 100% pilsner malt with 1 oz of hallertauer. (.5 oz at 60 and .5 oz at 20)  Mashed at 149 for 75ish minutes. Mashed out at 172 for 10 min. Fermented with WLP840 American Lager yeast at 52F until it hit 1.020 and then a d rest for 4 days at 60F.  OG 1.040 FG 1.015. no filtering, no finings.

[pete b]

Were you frying hot dogs in butter on bottling day?

[factory]

Were you frying hot dogs in butter on bottling day?

No, but my boil kettle doubles as a popcorn popper.   

[morticaixavier]

I'd say you got lucky. or they did ding you and just failed to note it on the score sheet.

[Jimmy K]

... or they did ding you and just failed to note it on the score sheet.

That's what I was thinking. Maybe it would have been a higher score without it.
 
factory - you could email the judges and ask. It wouldn't matter if it was butter from diacetyl or something else (I don't know what else it would be) because it's the flavor that is the problem.

[denny]

Just becasue they didn't mention diacetyl doesn't mean that it isn't.

[factory]

Got it. Consensus = diacetyl even if it wasn't specifically mentioned.  Now I have to figure out how to get rid of it next time. 

[hopfenundmalz]

Diacetyl can be confused with some crystal malt/caramel flavors. but I don't expect you used crystal malts in a light lager.

[Wort-H.O.G.]

i'm planning on running an experiment soon dosing wort with the amino acid valine. plan to split a 3 gallon batch into 3, 1-gal containers and ferment them. 1-no additions, 1- 300mg/L, and 1- 500mg/L.

i will be looking for perceivable differences prior to and after diacetyl rest. study i read (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708283/) indicated 37% lower diacetyl production for 300mg/L dosing, and closest to the flavour threshold (below 100 μg L for lagers). They ran tests on 100mg/L and 300mg/L with no impact to flavor, fermentation rate or final attenuation level. I'm curious to see if the 500mg/L has any noticeable impact on fermentation and taste of finished product - both any diacetyl perceived and finished beer overall flavor.

not sure if anything will come of it, other than some fun experimentation.

[Black Sands Brewery & Supply]

Got it. Consensus = diacetyl even if it wasn't specifically mentioned.  Now I have to figure out how to get rid of it next time. 

Caused in fermentation. Can also be formed from a pediococcus infection.

Many other causes. Low ferment temps are huge. Under pitched yeast can cause it, long time to cool wort, not allowing for full fermentation and a slightly warmer d-rest on primary.