I brewed a dry stout today and barely passed 60% efficiency even with milling my own grains. My mash was kept at 150-152F for 60 mins. However, I think I accidentally mashed with 0.84 q/lb instead of the normal 1.25 (added 2 gallons instead of 3 for a 9.5lb grain bill). Although I'm certain that's where my efficiency was lost, I was wondering how severe losses are when the water I use has a pH between 7.88-8.02 (2011 Water Report for Kingston, Ontario).
My last batch had an efficiency around 72-75%, so I know I can put out decent numbers.... but I'm just wondering where exactly my losses are coming from. I have nearly zero MLT deadspace, I always sparge with two equal amounts of water at 175F, The mash is always mixed to avoid doughballs and is stirred once during the 60 minute mash. Temperature varies along the depth of the MLT, so it's hard to tell exactly what temperature the grains are mashing at. This is really the only place I can see where I consistently lose efficiency. On top of that, my pre poil is 7 gal and post boil is 5.5 gal.
What could be the main cause of my efficiency evading the 80% mark? Would mashing for another half hour benefit me? I guess I should get some iodine and make sure that my starches are fully converted before extending my mash time, but I'm also interested to see how long others are mashing for.
Thanks for the help!