ljm
Member
I have been redoing my spreadsheet attempting (among other things) to eliminate gravity points from recipe calculations.
Starting from m = V*SG*d*P
m = mass (kg) extract
V = recipe volume
SG = specific gravity of wort
d = density of water at 20C (kg/L) = .998203
P = degrees Plato
Here are the results with 4.5359kg (10 lbs) of 2-row, in a batch volume of V=18.927L (5 gal),
m = 3.55208kg.
Method 1:
Nothing fancy, just 72.3804 maximum gravity points with SG = 1.0724, P = 17.601 (ASBC polynomial).
Method 2:
Substitute SG = 1 + P/(258.6-P/258.2*227.1)
This gives a quadratic (nice) in Plato = 18.787 -> S = 1.0776
Method 3:
Substitute for P with the ASBC poly: -616.868+1111.14SG -630.272SG^2+135.997SG^3
The subsequent quartic equation is not nice. So I used an online solver to get S = 1.0011 which is even worse. An error on my part is possible, but I tried it a few times with and without consolidating the constants.
Well, says I, method 2 is a bit off from the point system, but as much as I respect empirical work, the 42.xxx pppg (38x.xxx LDK) always seemed a bit squiffy.
So I tried a grain amount more in line with my typical starting max gravity using 5.443kg (12 lbs) 2-row. Here are the max values.
Method 1: S = 1.0869 -> P = 20.869
Method 2: P = 22.541 -> S = 1.0944
Not very good agreement at all. Things are getting worse.
Even at 5 lbs of grain, method 2 gave 37.5 pts versus method 1 at 36.2. So what gives? I expected ASBC would be an improvement. I realize these max gravities might be pushing the ASBC polynomial, but Geez...
So which should I trust more? Method 1 or 2 or none of them? (I really don't want Method 3 anyway 'cause it doesn't fit into a spreadsheet.)
Thanks in advance for some input.
LJM
Starting from m = V*SG*d*P
m = mass (kg) extract
V = recipe volume
SG = specific gravity of wort
d = density of water at 20C (kg/L) = .998203
P = degrees Plato
Here are the results with 4.5359kg (10 lbs) of 2-row, in a batch volume of V=18.927L (5 gal),
m = 3.55208kg.
Method 1:
Nothing fancy, just 72.3804 maximum gravity points with SG = 1.0724, P = 17.601 (ASBC polynomial).
Method 2:
Substitute SG = 1 + P/(258.6-P/258.2*227.1)
This gives a quadratic (nice) in Plato = 18.787 -> S = 1.0776
Method 3:
Substitute for P with the ASBC poly: -616.868+1111.14SG -630.272SG^2+135.997SG^3
The subsequent quartic equation is not nice. So I used an online solver to get S = 1.0011 which is even worse. An error on my part is possible, but I tried it a few times with and without consolidating the constants.
Well, says I, method 2 is a bit off from the point system, but as much as I respect empirical work, the 42.xxx pppg (38x.xxx LDK) always seemed a bit squiffy.
So I tried a grain amount more in line with my typical starting max gravity using 5.443kg (12 lbs) 2-row. Here are the max values.
Method 1: S = 1.0869 -> P = 20.869
Method 2: P = 22.541 -> S = 1.0944
Not very good agreement at all. Things are getting worse.
Even at 5 lbs of grain, method 2 gave 37.5 pts versus method 1 at 36.2. So what gives? I expected ASBC would be an improvement. I realize these max gravities might be pushing the ASBC polynomial, but Geez...
So which should I trust more? Method 1 or 2 or none of them? (I really don't want Method 3 anyway 'cause it doesn't fit into a spreadsheet.)
Thanks in advance for some input.
LJM