When To Measure Pre-Boil Gravity Reading For Efficiency Calculation?

I'm using BeerSmith for my brewing software, and it measure efficiency for you.  I have to take a gravity reading, pre-boil, however I'm not sure when I should do it.  I'm brewing 10 gallon batches, so when my wort starts out in the boil kettle, it is a bit below 10 gallons.  I then add water to get to 12.75 gallons so at the end of the boil I'm back to 10 gallons after burn off.  So, should I be measuring pre-boil gravity...

a) once I've transfered my wort to my boil kettle (it's below 10 gallons at this point)
b) top up to 10 gallons to represent what will be the final volume in my fermenters
c) top up to 12.75 gallons

I'm guessing the answer is b as it represents what my final volume will be, but I just don't know.

Cheers!

Do you all-grain?  If so, as you are draining first runnings from tun I measure OG there to get my mash efficiency.  Preboil gravity would be after you get to your pre boil volume.  IE, after you add top off water for 12.75 gallons.

Mark

All grain all the way!

I just realized I was incorrect in my above post.  I measure OG from as it's about to enter the fermenter, not pre-boil.  However, what you stated below is good to know. 

Cheers!

merfizle said:

Do you all-grain?  If so, as you are draining first runnings from tun I measure OG there to get my mash efficiency.  Preboil gravity would be after you get to your pre boil volume.  IE, after you add top off water for 12.75 gallons.

Mark

Click to expand...

Pre-boil gravity should be taken after all the grains are in the wort and the total pre-boil volume is met, in addition the sample should be cooled for an accurate reading. This way you have the ability to adjust the wort for proper gravity with either more water or some DME. Cheers!

Hibs
All of this measure is to determine how much sugar (maltose) you have in the wort.  The preboil SG from BS is based on the total volume of water before the boil;  this will be after you have top over the kettle to the 12.75 gallons.  The Original Gravity is the target from your recipe and that is based on the volume you put in the fermenter.

I tend to keep track of total sugar content;  The Specific Gravity will change each time you add water (top off) or remove water (boil), however the total sugar content will remain the same.  The easiest way to calculate this is based on "Points"  Points are the last two digits in the SG, ie 1.050 = 50 Points per gallon.  To get total points multiple by the gallons.  If your target is a Original Gravity (into the fermenter) = 1.050 in 10 gallons you have a total of 500 points.  If you measure this same wort with 12.75 gallons you SG will equal 500 / 12.75  =  39 points per gallon or SG = 1.039.

David