Boil off/ evaporation/ brew math and baffled

[duffstuff]

Hey guys I am completely confused sonim gonna get straight into it . I brewed a beer this evening and after a 90 min boil I only jumped 10 points on the hydrometer . My equipment has been calibrated and the only variable is that my measure stick may be off.
Heart are some numbers , please help if you can..
Grain bill 11lbs pilsner , 2 lb Munich.
Pre boil gravity was 1.050. Assuming measure stick is accurate it was 7.5 gallons.
I'm new to brewing equation but I thought I had it nailed .
With the information above I calculated 78 % efficiency.
Boiled down to an assumed 5.5 gallons and my OG is reading 1.060 . That was a 90 min boil. I think all the info is there . If anyone can shed some light on where I'm going wrong , that would be great. I hope it's something easy but I just can't see it .
If I am right I should be way higher . 1.080 ish. ?? Is there a possibility I boiled off way less .
Living in humid Korea at the moment if that is another variable.
Anyway thanks in advance for any help anyone can give.
Cheers , duff

 

[erikpete18]

Well, for starters, if your pre-boil readings are all correct, that should give you (7.5*50=) 375 gravity points. After boiling, and again assuming that your measurement of 5.5 gallons is correct, that should give you a final gravity of (375/5.5= 68) 1.068, so you're not as far off as you think. If your volume measurements are slightly off, I could see that making up that last 8 points somewhere.

You may also want to take a look at how you're taking your pre-boil reading. If you're not stirring the wort before taking your reading real well, its possible that you're only reading a subset of the wort rather than the whole gravity. I would think normally that would mean that you're taking it from the top where the sparge water is making it read lower, but in your case it would only make sense if you're taking it from a spot of higher gravity. Might not be the case, but just something to think about.

 

[duffstuff]

Thanks for the input. I'm just baffled by the jump from 1.050 to 1.1060 After a 90 min boil , I've never had so little boil off.
Thanks again for the answer , ill keep working at it too ha

 

[smyrnaquince]

Boiled down to an assumed 5.5 gallons

Living in humid Korea at the moment if that is another variable.

Did you measure the 5.5 gallons or assume it based on your boil time?

I get a lower boil-off in hot and/or humid weather than I do in the winter. If you did not actually measure your final volume, then this may have happened to you, as well.

Did you let the sample cool before taking the final gravity reading? I believe that the corrections for temperature get less reliable the hotter your sample is.

 

[duffstuff]

Thanks for the reply . I assumed the 5.5 based on time and previous brews but I did wait for the right temp for my hydrometer reading