I have an american lager that fermented at ~54 for 2 weeks. Obviously no visible fermentation going on, but was wondering if i can get any benefit from a 65* diacetyl for a few days?
You can perform a forced diacetyl test to check if diacetyl is present. It’s somewhat of a pain to do, but it’s better than packaging and finding it later.
Warming it up for a few days at this point certainly will not hurt anything. But how does it taste?? If it doesn’t taste like diacetyl, then why worry about it. If it does, then you can warm it up and hope for the best. If warmup doesn’t work, then add a vigorously fermenting yeast starter. Nothing else will clean it up but live yeast.