For context, I do 2.5-gallon stovetop BIAB AG brews.
Two brews ago, my mash temp got away from me (I didn't allow for continued heating from the electric coils on my stove after turning the burner off) and I mashed at 158 F. My extraction efficiency was 77%. With yesterday's brew, I paid attention and mashed at 154 F. That brew had an efficiency of 85%.
From Palmer's book, I recall that beta amylase is denatured at higher temperatures and I was wondering if this might explain my lower efficiency in the earlier brew and the higher efficiency in the later brew.
Everything else was pretty much the same (90-minute mash, squeeze the heck out of the bag) except that the earlier brew had a mashout at 172 F and the later brew at 170 F. For the efficiency calculations, the max sugars were based on actual grain weights and gravities, not averages, and the actual sugars extracted were based on the start of boil volume and gravity.