BeerSmith always gives me starting OG higher than seems possible

[klnosaj]

I'm x-posting this from General Techniques. I figured maybe someone here could help me figure out why I'm consistently missing the OG BeerSmith predicts despite hitting correct pre-boil gravity and having the correct post-boil volume.

The past two beers I've made have had the same problem. My pre-boil gravity is spot on. My pre-boil water volume is spot on. My post-boil water volume is spot on. Yet my post-boil into-the-fermenter original gravity is low. Isn't that kind of impossible?

Here are the details today:

------------------estimated -------measured

pre-boil SG---------1.040------------1.040

pre-boil H2O vol----7.0 gal-----------7.0 gal

post boil SG--------1.049------------1.043

post-boil H2O vol---5.25 gal----------5.25 gal

all estimates provided by beersmith 2.0, all measurements cross checked between hydrometer and refractometer, post-boil SG taken form two independent samples.


What is going on? I'm going crazy over this!

This should be the easiest calculation of all, shouldn't it? If pre-boil volume is 7.0 gals and pre-boil gravity 1.033 then post-boil volume of 6.0 gals assuming a boil-off of 1 gal HAS to be 1.0385, right? Since 33 gravity points in 7 gals = 231, the same points in 6 gallons = 38.5. So why does beersmith tell me that my post-boil gravity should be 1.041? (My equipment profile is correct.)

Is it possible you're doubling counting losses somewhere trub, volume, etc.)?

aka, you're entering a corrected value and beersmith is also "correcting" it?

I don't think so. And what's annoying is that the post-boil numbers add up. As I've admitted I can be sloppy with my volume measurements but there's something that just doesn't make sense to me in how beersmith is calculating the number. If I have x gravity points in y gallons of water than the points I have in y-boiloff is an easy thing to calculate. But beersmith is getting it wrong.

I'm wondering if it doesn't have something to do with temperature and expansion under temperature. I begin with 7 gallons of H2O at room temperature and use that for mashing and sparging. I then put 7 gallons of wort, now around 160F into the kettle and boil that for an hour until I have 6 gallons of ~212F. That shrinks and I toss the trub and I'm left with 5.25 gallons of room temperature wort. So is the software making assumptions about temperatures or something? I would LOVE it if someone could explain this to me.