Minimizing diacetyl in lagers

TroubleShooting

Darrin Burchell • Paris, Kentucky asks,

I have just started brewing lager beers, but have had problems with my first batches. The problem is the production of diacetyl. I just can’t seem to get rid of it. I believe that I am following good lagering technique, but my beer tastes like a butterscotch sundae. Here is what I am doing: After wort production, 5 gallons (19 L) total, I am chilling the wort to 52 ºF (11 ºC) overnight. I then pitch a 2-quart (~2-L) slurry of yeast, the strain is Wyeast 2007 Pilsen Lager Yeast. I ferment for two weeks at 52 ºF (11 ºC), then raise the temperature to 60 ºF (16 ºC) for three to four days to finish the fermentation. I chill the beer down to 32 ºF (0 ºC) at a rate of 4 ºF (~2 ºC) per day. I rack the beer to a keg for final lagering and lager at 32 ºF (0 ºC) for four weeks. The problem is that I cannot taste the diacetyl in the green beer, I can only detect it after the lagering period. I am trying to salvage this batch by depressurizing the keg, pitching a fresh slurry with a little extra corn sugar to feed the yeast as a makeshift kraüsening method, then refermenting at 60 ºF (16 ºC) for a couple of weeks and relagering. I am fairly experienced with sanitation, but I cannot completely rule out contamination without a microscope. I have produced many good ales with no contamination in the past. Is there any hope or am I an ale drinker for the rest of my days?