So, I've done probably 6 or so 5 gallon AG batches, and I'm almost right on 67% efficiency every time. It's not the best, but I'm happy with the consistency over the efficiency.
last weekend I stepped my normal brew day up, and did a 10 gallon batch of a new IPA recipe I was trying. The only thing I changed was that I decided to mash at 156 rather than the 152 I normally do, as I'm starting to wonder if my thermometer was off. Long story short, I ended up with 85% efficiency! It worked out well because I accidentally added about a gallon more water than necessary, and ended up hitting my OF perfectly, with an extra gallon of beer.
Did stepping up from 5 to 10 gallons have some drastic change in efficiency? Like is the extra weight of all that grain squeezing something out of the grains below it? I noticed I ended up running off more liquid than I usually do from the grain, maybe an additional half gallon. Or do you think the change in temperature was more likely the cause, and I just happened to push the temperature up into a reasonable mash temperature?
Oh, random story, it started snowing just as I mashed in. There was no turning back. Turned out to be a really frustrating brew day, had to throw up a tarp on my deck just so I could boil in peace not being covered in snow It was cold and windy and took a lot longer running in and out all afternoon but it was still a lot of fun.