« on: December 08, 2013, 02:36:50 PM »
If it's not an infection, but merely precursor oxidizing to diacetyl, next time you could let the ferment temp rise before you hit terminal gravity. That will keep the yeast working faster and longer. 61F is pretty cold. You could also try the forced diacetyl test described in the White and Zainasheff Yeast book. That will let you know if you have too much precursor before bottling. If so, you wait longer to let the yeast finish up.