poor mash efficiency

[Dutchbrew]

the week before i had a great mash effeciency using my cooler prob 80% or 85%... This time however I calculated a efficiency of 50%. The only thing i did different this time was i grind my own grain using a corona type grinder. I had the setting to grind pretty course which I would think would be ok and i could tell most of the grain was all cracked. Should I try a finer grind setting next time. Are you usually suppost to use a fine grind setting ? not sure on this.

[BillyBock]

Unfortunately, the crush of your grain has a lot to do with efficiency. You not only want to be able to crack the grain open, but you want to expose enough of the kernel so the enzymes can work on the starches. Crush finer--but be careful not make flour. On other boards you'll probably hear the mantra...'crush 'til you're scared.'