Originally Posted by BigKahuna
NOt enough sparge water.
I had this exact issue, and started to realize that if I had a grain bill of 9#'s or less, I was getting 75%+ and the more grain I used, the worse it got. I think if you were collecting closer to 9 gallons from that 12# of grain, you would be closer to the mid 70's
9 gallons, really? My last brew had an expected OG of 1.056, and I collected 7.4 gallons. The LAST runnings were at 1.008 (about the min. unless you want to start extracting alot of bad stuff). Now I also did a 90 moinute boil, and I had the exact same eff. as when I ran off 6.7 gallons and boiled for 60 minutes.
Basically, there is no point in running off more into the kettle than necessary. If you plan for a 90 minute boil, the pre-boil volume will probably put you at the MAX that you can run off, meaning anything more and there wont be enough sugar in it to matter at all.
If I collect 9 gallons, I would have to boil for 2 hours and 38 minutes to get down to 5.3 gallons!