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Final Gravity estimation way off in Plato, but correct in SG units

Maxo

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Hello,
I use Plato units and noticed that estimated FGs are off. I have "Adjust FG for Mash Temperature" unchecked (Options>Advanced), so that Mash Profile doesn't affect FG estimation and Yeast min and max attenuation set to same value. So I tried this:

OG: 20P
ADF: 80%
FG: expected 4, BeerSmith = 4.26

OG: 20P
ADF: 70%
FG: expected 6, BeerSmith = 6.34

For SG units it works flawlessly
OG: 1.080
ADF: 80%
FG: 1.0160






 
Plato is not linear with specific gravity.  The relationship is defined as: SG = 1+ (plato / (258.6 – ( (plato/258.2) *227.1) ) )

When calculating apparent attenuation, specific gravity is used, so trying to apply the same calculation to degrees Plato will give you an error.

 
Thanks, that explains BS behavior. Now it gives me acceptable error of +0.03P
20P = 1.0830
1.0830 * (100-80)% = 1.0166
1.0166 = 4.23P [vs 4.26P in BS]

I'm just not sure why ADF should be measured in SG and not the other way. Plato is unit of sugar percentage in soution, and ADF is measured by (apparent) percentage sugar left after fermentation. SG is weight unit in relation to water. I doublechecked book Handbook of Basic Brewing calculations from Master Brewers Association of Americas that refers to some known industry books, and they use Plato for ADF.

To test linearity of results, I changed plato ADF from 80% to 79.6% to match 20P case
20P=1.0830 SG
20P*(100-79.6)%=4.08P=1.0160 SG
1.0830*(100-80)%=1.0160 SG

15P=1.0611 SG
15P*(100-78.85)%=3.06P=1.0120 SG
1.0611*(100-80)%=1.0122 SG

12P=1.0484 SG
15P*(100-78.85)%=2.448P=1.0095 SG
1.0484*(100-80)%=1.0097 SG

It is acceptable error

Thanks once again :)

 
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