# Pre-boil gravity (PBG) calculation

Discussion in 'Recipe Editor' started by PZ, Sep 20, 2017.

1. ### PZ Member

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#1
Hello BF,

This topic has been raised a few times, so I thought I would present the problem in a simple way. The PBG represents the total amount of sugar at the start of the boil. When boiled, the wort has the same amount of sugar, but in a smaller volume. That volume should be the ending kettle volume regardless of how you calculate brew house efficiency. (Of course, there are additional calculations for late additions, but this is the simplest case.) Therefore:
PBG*starting boil volume/ending boil volume = OG
Or
OG*ending boil volume/starting boil volume = PBG

where the specific gravity observations are SG-1. It's even easier to do the math in your head if you then multiply by 1000 so SG of 1.050 becomes 50.

My only other thought is that PBG is irrelevant in a recipe -- it only becomes important on brew day.

It would be great if this could be fixed. Thanks, PZ

2. ### Trialben Well-Known Member

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#2
Preboil for me is an indicator of my mash efficiency and if I'm track. I'm happy the way it is.

3. ### Mark D Pirate Well-Known Member

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#3
Boil gravity affects hop utilisation so is important to a recipe .
Frankly I don't see why OP would want unspecified changes made to software that works well already

4. ### PZ Member

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#4
Because the calculation is incorrect. It uses the fermenter volume instead of the kettle volume. Do the math. Other people have voiced the same complaint so I thought I would try again.

5. ### Ozarks Mountain Brew Moderator Staff Member

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#5
you right there, in recipes I always set it to kettle, fermenter doesn't work

6. ### Mark D Pirate Well-Known Member

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#6
Hmm mine is always within a point or so , will check on PC tonight and double check next brew

7. ### Ozarks Mountain Brew Moderator Staff Member

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#7
well its relative really you can set your profile and losses for one or the other and neither are wrong

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