This weekend I did two brews, one was a India Red Ale and the other a Delerium Tremens clone. I've made both recipes before without issue. But, this weekend BOTH of my pre-boil gravities came in well below what they should have been (46 instead of 56, and 40 instead of 46). I batch sparge, and like I mentioned, batch sparging both of these recipes previously has been fine. Also, my infusion temps were hit exactly at 153 for the IRA and 146 for the DT clone. Temp checks at the end of each mash confirm the temps stayed constant the whole time.
I can only think of two possibilities for the low pre-boil gravities.
1) Maybe the pre-set mill at Northern Brewer here in Milwaukee was off and I didn't get a good crush. It looked ok, and I've used that same mill before without trouble, but who knows? Anybody in the Milwaukee area have a similar experience with NB?
2) I usually store my crushed grain until use in a chest freezer with a temp control at 40 degrees, but this time I accidentally left the temp probe outside of the freezer. So the grain froze then I thawed it by leaving it at room temp overnight before I used them. Grain temps were 52 degrees when I mashed in, and I adjusted mash water temp to ensure I hit my mash temp. Could freezing the crushed grains cause this kind of a problem?