SWIM heated at around 120F in the oven and 250 mg were still quite active.  His extraction methods were a little less refined at the time, and SWIM suspects that it even had more impurities than his recent yields.  SWIM will find out soon if his more recent yields are decently active.  Stove tops can get quite hot, though.

Sorry for SWIY's loss.  SWIM's quite reassured to hear that 155F seems to work well.