Acetylaldehyde:
Chico yeast - US-05, WY-1056, WLP001 - cool temps and/or underpitching seem to increase acetylaldehyde, I stick in primary for 2-3 weeks now depending on gravity, with a rise to 70F for the last couple of days.
DMS:
What is your boil off rate, if it's below 8% or so that could...