Boil doesn't change gravity?

[Berk]

So I know I lose 3L/hr, which is punched into the software. I know my pre-boil gravity and I can always predict the volume loss. The problem is that I can never seem to predict the gravity gain from boil. For example my last boil didn't seem to gain any gravity points, after an hour boil and checking with hydro and refrac. Seems impossible. I've re-calibrated etc but have resorted to hydros for that reason and made sure everything's at temp. What the? Any ideas?

 

[wide eyed and legless]

So I know I lose 3L/hr, which is punched into the software. I know my pre-boil gravity and I can always predict the volume loss. The problem is that I can never seem to predict the gravity gain from boil. For example my last boil didn't seem to gain any gravity points, after an hour boil and checking with hydro and refrac. Seems impossible. I've re-calibrated etc but have resorted to hydros for that reason and made sure everything's at temp. What the? Any ideas?

I think it's your reading of the pre boil gravity which is out, the wort needs a good stir to mix in the higher density wort from the bottom.

 

[Kev R]

Are you checking at the same temp?