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Discrepency between brewsheet and boil off calcula

Andrewqld

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Hi,
I have entered a recipe for an Alt and in the brewsheet it says.
That my boil volume after sparging should be 29.95l @ 1.038 and after a 60 min boil and a 20% loss I should have 23lt@1.050
However when I punch these figures into the boil off calculator it gives me a gravity reading after the boil of 1.048.
Why is there a 2 point difference. Shouldn't they matchup?

Thanks for the help
Cheers
Andrew
 

BeerSmith

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Andrew,
 Yes it should be the same.  Could you send me a copy of the recipe?  In some cases settings in the recipe may be affecting the calculation.

 I would certainly like to take a look at it - so please email the recipe to me.

Thanks,
Brad
 

BeerSmith

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FYI,
 For those interested - the difference comes from the fact that the recipe system includes the volume loss for cooling (4% by default) while the boil off calculator does not.  This results in a slight difference in final volume and OG.

Cheers!
Brad
 

Andrewqld

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I see what you mean Brad, if i take into consideration the 4% shrinkage on the above figures then I end up with 1.050.
The question I have is: Why does shrinkage affect final gravity? If I take an sg reading from the kettle just after the boil it should be the same as after the wort is cooled. I know the shrinkage affects your overall EFFICIENCY but your sg reading should not vary because volume is not related to the sugar content when taking an SG or Brix reading.
Sorry for wasting your time, I just find this a bit confusing. Hope you understand what I am trying to say here, it even sounds strange to me.

Cheers
Andrew
 

BeerSmith

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Andrew,
 SG is related to volume.  The same amount of sugar in a lower volume results in more concentration and a slightly higher SG.

Cheers!
Brad
 

Andrewqld

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yes of course, sorry Brad that was too obvious for me to see, basic brewing and I forgot it.
Any chance of adding shrinkage option to the boil off calculator in the form of a check box? That way it could be used for pre cool as well as post cool.

Cheers
Andrew
 

BeerSmith

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Yes,
 I should add it to the boil off calculator and it is not that hard to add.  I will put it on my "to do" list which I am slowly working through right now.

Thanks,
Brad
 
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