Mashing Help Please (efficiency)

[TheCrowBrew]

For some strange reason I cannot get a 75% efficiency, my best close to 70%. I have a square cooler box mash tun. My last two was 50 and 60%. I am doing batch sparging. My grains are milled by a brewer, so I think that is not the problem. My last mashing was done at 66C (150F) constantly for an hour. So my temps are on the dot.

My last order was a bag of 18kgs (40lbs) pale malt. So maybe i am scooping more husks than grains?

Help please! I cannot understand why it is so bad!!!

 

[freisste]

How big are your beers? High gravity brews tend to have lower efficiencies. Have you checked your thermometer(s)?

 

[kenny_d]

What about mash ph? The enzymes like certain ranges!

 

[unionrdr]

I'd be concerned about the quality of the crush. When I get pre-crushed grains, they aren't crushed very well & I have to do a second crush. I git my own grain mill & crush'em myself now. With batch sparging I get higher OG's all across the board.