About 10 days after transferring a cider to secondary, it developed a faint diacetyl aroma. I moved it to a warmer location (~70degF) for a few days for a diacetyl rest, but the smell is now more pronounced.
I am considering the following next steps:
If it is from bacteria, I am considering shocking it with campden and adding fresh yeast and a little sugar to allow the yeast to metabolize the diacetyl.
If it is from the yeast, I will give it more time unless there are other recommendations.
Toss it if it is beyond repair. Diacetyl is the dominant aroma.
Background:
Yeast: Lalvin D 47
OG: 1.045
Cider: Pasteurized
Temp: 60 to 65degF
Two other batches started at the same time and temperatures but with different yeast (Nottingham Ale and Mangrove Jack M02) have not developed the issue.