I think if you were to warm the sample up a bit you would start smelling it again.
Maybe, maybe not. Yeast eats diacetyl. Yeast eats faster at higher temperatures. Therefore, yeast eats diacetyl faster at higher temperatures.
For the rest of ya'll...
Carnac says, "Di ac-etyl! Di ac-etyl!" with a sealed envelope on his forehead. Rips open the envelope...
"What you say when your daughter's scumbag boyfriend proposes because he knocked her up."
Not a very good one, but a modest attempt.