Lawrence Brewers Guild

I recently kegged an Octoberfest, and with the first sample, I was overwhelmed with butter, which I presume to be diacetyl. I’ve never had this happen before. Both aroma and flavor. Specifics:
This was a 2 gallon batch, an over run on a 20 gallon batch. Grain bill was 50/50 vienna, munich. 90 min mash at 149F. 90 min boil. Chilled to around 70F, then chilled to 45F for yeast pitch. I used a rehydrated pack of Danstar Munich yeast. (Used Wyeast Oct Fest blend for the 20 gallons, multiple step ups for a big pitch). OG 1050.
Left on primary at 50F 2+ weeks, ending with 36 hrs at 70F. Then crashed and pushed to secondary. Aged 4 weeks at 45F. Kegged last Saturday. Fermented out to 1012. Charged with CO2, and stored keg for serving at 45F. NO sign of diacetyl odor or flavor at kegging, but now, 4 days later, POW.
The 20 gal batch is in secondary, set to keg in a couple weeks. Scared it might have the same fate.
What happened?

I wonder, since no butter flavor at kegging, about infection (pedio in line or keg?).

Try a longer period at 70 degrees. If no change, pitch a vile of lager yeast and let sit for a week at 70.

Hope that helps.

John P.

Let's look at the yeast.

Danstar Munich yeast should be rehydrated carefully in plain water at 86 to 95 degrees, and temperature lowered to pitching temperature. Temperature shock, at greater than 10°C, may cause formation of petite mutants leading to long-term or incomplete fermentation and possible formation of undesirable flavors. What was the temperature of the rehydrated yeast when you pitched it into the 45 degree wort?

Normally, this yeast has a quick start and vigorous fermentation, which can be completed in 4 days above 63 degrees. It may have been sleeping in the cold temperature at 50, and most of the fermenting was done when you raised the temperature to 70.