Undershooting/ Overshooting Gravities

[Kate00]

Word

For my last few batches, Ive used Belgian Pilsner twice, and ive undershot my gravities by about 4 points. I did a Maris Otter pale malt and overshot my gravity by about 4 points. I think the culprit is an inconsistent crush from the mill at my LHBS, guessing that it was adjusted when I overshot, but a little loose when I undershot. Does anyone else have problems with missing high or low based on different malt types, or is it a milling problem?

The beer will be yummy regardless, just wanna know for consistency and recipe formulation.

Thanks

Edit: Additional Info. Im using Beersmith to formulate recipes. For both recipes where I missed low, I used the light body mash, mashing at 150 deg for 75 min (both belgian Pils). for the Maris Otter where I missed high, i used the medium body setting and mashed at 154 for an hour.

 

[Kate00]

Anyone? Bueller?

 

[Buna_Bere]

It could be a difference in the moisture content of the grains, or even the total protein content. There's an episode of Brew Strong on malt analysis that has some good info.

 

[bobbrews]

It could even be that your water measurements are not 100% accurate. If the instructions say "add 8.68 quarts water at 158 F" and then you add 8.68 liters, well then you just screwed up. Additionally, boiloff rate could be higher or lower than expected. So what you end up plugging into the parameters may not be entirely accurate.

 

[tre9er]

Pay close attention to the crush. Shouldn't be any uncracked grains whatsoever. If there are your efficiency will suffer. You want it fine with some husks to create a lauter bed, but no more coarse than that.