Please review my OG calculations

[bknifefight]

So here is my process for calculating my OG when brewing.
I use a refractometer and brew 10 gallon AG with batch sparge and do 2 sparges based on my mash tun being a little small.

These are rough estimates of numbers, I do not have my notes from Friday's brew.

First runnings: 3.5 gallons @ 20.5 brix
Second runnings: 4 gallons @ 15.4 brix
Third runnings: 4 gallons @ 12 brix

Totalling 11.5 gallons of wort. I will boil off 1.5 gallons over the hour.

So here is my calculation:
((gallons x brix) + (gallons x brix) + (gallons x brix))/total gallons

((3.5 x 20.5) + (4 x 15.4) + (4 x 12))/10


This will give me the total brix of all of my wort, and dividing it by 10 (final number of gallons) will show me what I will end up with after the boil.

I did this on my most recent batch and had a number that was higher than my measured brix at the end of the boil, so I would just like to see if anyone notices anything wrong with my calculation.

Thanks!

 

[runkelia]

Your average is not a bad way to do it, why not stir it for a minute and get a reading?
I used to measure the gravity of each runnings collected, then thought: whats the point?
I employ the keep it simple method: check gravity once before boil, and check post boil.
I know my methods are consistent and know my efficiency, therefore I know I will be very close to my target every time.

 

[RonPopeil]

Same here. My crush is consistently mediocre from LHBS. I know 74% is my magic number with a cooler tun, LHBS crush and batch sparge. Measure before the boil and in the fermenter.