I have gotten what I believe to be acetaldehyde (green apples, cider) in every lager I've made. I've never gotten it in any other beer, nor had any off-flavors in any other beer I've ever made. I sanitize like crazy, have glycol-mediated temperature control, so on and so forth. I've read major causes of acetaldehyde are oxidation (I transfer everything under CO2; beer never touches oxygen until the glass), infection, and incomplete fermentation. I don't see any of those being my issue, especially considering I've never had those problems with other beers. I cannot for the life of me figure out why I'm getting acetaldehyde, so I've come here for help. Perhaps the biggest help in identifying the issue is that I only notice it once the beer is crashed, kegged, and carbonated. Here's the last recipe and some notes as an example:
46% - Pilsner
26% - Munich
25% - Vienna
03% - Victory
20 IBUs total of Hallertau Mit. and Saaz at 60 minutes
Wyeast 2308 Munich Lager pitched at proper rate after starter
Fermented at 50 degrees for a week when activity stopped, then gradually raised to 67 for diacetyl rest.
Once final gravity was reached and no off-flavors detected (about two weeks), cold crashed to 35 gradually and then held there for another two weeks.
Kegged after cold crashing. Five weeks brew day to keg. Planned to continue to crash/lager in the keg with floating dip tube.
Any detectives out there who can spot what might be causing this? This is just one of about five lagers I've tried, some with different yeast, and they've all had acetaldehyde. I am at my wits end.