OK, time for another chapter in my elusive quest for efficiency gains. I've been averaging 72% using Denny's hose braid, then subsequently with a new copper collection manifold I made following John Palmer's guidelines. No difference, really. I have been watching the crush like a hawk, even double milling just to be sure. On my last session yesterday, my efficiency actually dropped to 67%. Really disappointing. I'm stirring thoroughly at dough-in, then again at 30 minutes, then stirring thoroughly before vorlaufing each of two equal sparge additions, and it all looks great. I'm hitting my water volumes spot on, but the pre-boil gravity comes in 4 points low. So, I boil longer to get the OG I want, which requires that I recalculate the hop timing to get the target IBUs. After 105 minutes, I finally get my target OG.
The guys at my LHBS just installed a new mill and they say their mash efficiencies have gone UP, to about 85%, and asked me to report how I did. Well, mine's going down. I have to say that this particular mash was designed to be pretty high gravity. I was going for an Imperial IPA at 8% ABV, so I used more base malt than before, adjusting the water volumes appropriately. Total grain bill = 17 lbs for a net volume of 6.375 gal. At 75%, I should have had 1.058 pre-boil gravity and 7.5 gal in the boil kettle (corrected to 68 F); volume was good, but the gravity was 1.054.
What's up?!?