I expect this question has been addressed in other threads, but I hope someone can answer this perplexing question. It has happened to me several times - but not every time. I made a partial mash IPA yesterday. The malt bill was 10.7 lbs (including 6 lbs of light DME and .5 lbs of Dextrose). I mashed the remaining 4.2 lbs of grains for 60 minutes at 150 degrees. I batch sparged the finished mash with about 2 to 2.5 gallons of 170 degree water to end up with a 3.5 gallon boil. Upon finishing the boil and topping off to 5 gallons, the OG was a mere 1.043 versus the anticipated 1.058. This seems impossible considering the 6.5 lbs of DME and Dextrose alone - per the calculators - should produce an OG of about 1.054 for an anticipated ABV of 5.10%. I suspect it has to do with the mash efficiency - but I only mash in order to add specific flavor characteristics to my beers. Thanks for any suggestions.