Pre-Boil Gravity Calculation question

Hello,

First, let me say great program.  I've found it very useful to tweak various recipes to my own equipment.

However, I seem to have one question on how the calculation of the Pro-Boil gravity is calculated with respect to the equipment -- specificially the "Lost to Trub and Chiller".  It's certainly possible that I'm simply using the tool incorrectly, so some help is appreciated.

In my equipment setup (iglo cooler/10gal brew pot), I estimate I lose about 1.75 gallons due to the trub/chiller (after whirlpooling, I just can stand siphoning up any of that sludge).  I like this part of the tool because it will automaticallly force to use more water (and grain) so at the end, i have 5 gallons of beer.

Now, when I've used the tool, I noticed that my measured pre-boil gravity (I always chill my samples to the calibrated temp) was significanntly higher than that of the brewer sheet calculation.

But, if I took "my" gravity readings and calcuated using the "boil off" tool, the calculated OG was on par with the brew sheet.

Anyway, a little investigation showed that if I went back and set the "lost to trub and chiller" to 0 qt, then the spreadsheet showed a consistent "pre-boil gravity".  (yes, It also recalcuates the water usage).  If I run the calculalted pre-boil with the "boil off tool", the brew sheet numbers are consistent.

This leads me to believe that this additional lost volume to the trub is being used in the pre-boil gravity calculation.  but, loss of pre-boil stuff shouldn't affect gravity because it carries both sugars and water.

Anyway, I hope this makes sence.  I'd appreciate any suggestions.

Thanks,
Stephen

Hi Stephen,
  In the last two weeks I've had a long series of email exchanges with another brewer on this very topic!  The recipe system uses a pretty simple model for calculating pre-boil gravity based on efficiency and grain contributions - similar to what you might do on a spreadsheet.  However, given that I have in BeerSmith the additional information available to calculate a more accurate pre-boil gravity based on the equipment settings, boil off, trub loss, etc...it is very possible to calculate a more accurate pre-boil gravity - much along the lines of the boil off tool.
 
  The bottom line is that I agreed with him (and you) and have already incorporated this into the next version of BeerSmith that I'm developing.  In the future the two tools will be consistent.  I have no hard date for release as I'm still working on several of the larger features, but it will be a free upgrade for all registered users.

Cheers!
Brad