Wondering why you are getting that low mashing efficiency, even though you optimized your mash tun design and milling gap?
That can be caused by using the wrong malt potential, specially on the base malts that represent the big chunk on your grain bill.
So after having this same issue for a while, decided to do my homework and investigate the base grain malt analysis from manufactures like Briess and calculate the gravity potential myself.
That in fact correct my efficiency calculations and allowed me to do better OG predictions.
The basic numbers you need to get from the malt analysis sheet are two:
DBCG = Dry basis coarse grind
MC% = Moisture content
The potential in PPG, which is point per pound per gallon would be calculated as:
Malt "Briess 2Row brewerrs Malt"
How to use PPG?
If your PPG=35 from the example above, that means if you use 1 pound of this malt to produce 1 gallon of wort, you would get 1.035 gravity or OG if your mashing efficiency was 100%.
Your OG can be calculated as:
MW = pounds of malt used
BV = Batch volume in gallons
EF% = Mashing efficiency
MW = 1000*(OG-1)*BV/(PPG*EF%/100)
You want your OG to be 1.050 on a 5gal batch and estimate your mashing efficiency at 70%, so the base malt weight your need is (for Briess 2Row brewers Malt) :
MW=10.2# of malt
I downloaded several spec sheets from Briess.com and calculated each malt PPG. I used mostly Briess malt so here's a table I use:
Click to see it bigger