Ok. So I know the difference between pre-boil and original gravity is basically a product of concentration after boiling. Yesterday my pre-boil 7g was 1.051. I boiled 60 minutes and had 5.5 gallons to go into the fermenter. My original gravity was 1.050!! I made sure both readings were at room temp. The only difference is that there was a ton of trub in the thief jar in the 2nd reading. What gives?
That's what I am thinking. Now knowing how much malt I started with, 16lbs. Assuming at least 60% efficiency and knowing how much I put into the fermenter I can only conclude I have my 1.071 like I should. I was not sure the trub affected it somehow. Time for a refractometer....
Trub doesn't affect gravity (because it's not dissolved) and shouldn't affect a hydrometer reading, unless there's so much of it (picture a proteinaceous hop wad) that it's a physical barrier and prevents the hydrometer from sinking. In that case, the hydrometer reading would be too high. But in your case, the reading was too low.
