Hi,
First off, love the software. It's an invaluable tool for preparing and running a successful brew day.
I'm wondering if the calculation that BeerSmithuses to predict post-boil OG may be slightly off?
My understanding is that the formula used to calculate the predicted OG is:
At the moment, it appears that BeerSmith uses the non-cooled volume (i.e. thermal expanded volume) for the pre-boil volume. If the cooled volume is used for the pre-boil volume, there is a difference of several gravity points.
An illustrated example:
Pre-Boil Vol:
(volume at 77C)
Pre-Boil Vol factoring shrinkage (Assume 3% @ 77C):
Pre-Boil Gravity:
Post Boil Vol (@25C):
Formula 1: Raw pre-boil volume
Calculation:
Calculation:
=> Post Boil OG:
Formula 2: Equivalent Pre-Boil Volume factoring shrinkage
Calculation:
Calculation:
=> Post Boil OG:
Formula 1 appears to match the numbers I get out of BeerSmith, but my feeling is that Formula 2 is the way the OG should be calculated?
Is this a bug, or have I misunderstood/miscalculated something above?
Simon
First off, love the software. It's an invaluable tool for preparing and running a successful brew day.
I'm wondering if the calculation that BeerSmithuses to predict post-boil OG may be slightly off?
My understanding is that the formula used to calculate the predicted OG is:
Code:
(Pre-Boil Vol x Pre Boil Gravity Points) / Post Boil Vol = Post Boil Gravity Points
At the moment, it appears that BeerSmith uses the non-cooled volume (i.e. thermal expanded volume) for the pre-boil volume. If the cooled volume is used for the pre-boil volume, there is a difference of several gravity points.
An illustrated example:
Pre-Boil Vol:
Code:
63L
Pre-Boil Vol factoring shrinkage (Assume 3% @ 77C):
Code:
61.16L
Code:
1.075
Code:
55L
Formula 1: Raw pre-boil volume
Calculation:
Code:
(Pre-Boil Vol x Pre Boil Gravity Points) / Post Boil Vol = Post Boil Gravity Points
Code:
(63*75)/55=85.9091
=> Post Boil OG:
Code:
1.086
Formula 2: Equivalent Pre-Boil Volume factoring shrinkage
Calculation:
Code:
(Pre-Boil Vol factoring shrinkage x Pre Boil Gravity Points) / Post Boil Vol = Post Boil Gravity Points
Code:
(61.16*75)/55=83.4
=> Post Boil OG:
Code:
1.083
Formula 1 appears to match the numbers I get out of BeerSmith, but my feeling is that Formula 2 is the way the OG should be calculated?
Is this a bug, or have I misunderstood/miscalculated something above?
Simon