I brewed a brown ale today that I expected to get 75% efficiency on and to have an OG of 1.055. I'd plugged in all of my grains and brewing info into a brewing calculator. I run my second runnings in with my first runnings for a preboil volume of 7 gallons, take a sample, cool it to about 70. I take the reading with my hydrometer and my preboil gravity is 1.056 and my efficiency is 87%. Ok, so my efficiency was higher than I expected it to be for some reason and I figure my beer will finish in the mid 1.060's. Oh well. I'll fix it next batch. I boil my beer down to 5.8 gallons (overdid it a bit and meant to hit 6 gallons.). I pull a sample out of my pot as it's chilling, cool my sample to 70-72, drop in my hydrometer aaaaaaaand..... 1.054.
Now, this clearly makes no sense that my original gravity would be 2 points less than my preboil gravity. It should obviously be in the 1.060's. I believe that my post boil gravity was the correct one (although maybe I just want to believe it is.) My conundrum is that I have no idea how it happened. It makes no sense. The only thing that I can think of is that I when I ran my second runnings into my first runnings I didn't stir them together. Maybe I pulled from a more concentrated area or something. Any ideas as to why this may have happened would help with my sanity grestly.