Thanks for explaining.

In my example above the fine grind extract percent is:

37 (pppg of malt) / 46 (pppg of sugar) = 0.80435 = ~80%

12 lbs of malt * 0.80435 = 9.6522 lbs of fermentable and unfermentable starches

9.6522 lbs / 5 gallons of water = 1.23067016 SG -or- 49.5 Plato

Is that what you're attempting?

Not really, but getting closer. Thanks for replying. I guess I am not very good at explaining.

I am starting with a percent extract from whoever makes the grain. Eventually CGAI, but for now I just need a working percent. This is the same percent from which your example of 37pppg is derived. (0.80 * 46 = 37)

For example Briess has Brewers Malt with CG extract = 80.0% and moisture 4.2%. That makes CGAI = 76.6% which would be the maximum extract I could expect if I had 100% efficiency.

With 5kg (working with the metric system makes some of the math more transparent - my preference), I could expect a maximum extract of 3.83kg = m in the equation of the first post. With my efficiency, this mass would be multiplied by 75%. It is not necessary at this point to show the method, but lets do it anyway: .75 * 3.83 = 2.8725kg. I won't round until the bitter end to minimize significant figure errors.

For a batch volume of 20L (wort, not water), this maximum extract could also be found by (

*I think*) the formula presented in the first post:

m = V*SG*d*P

m = mass (kg) extract = 2.8725kg

V = recipe volume = 20L

SG = specific gravity of wort

d = density of water at 20C (kg/L) = .998203

P = degrees Plato

But I know the extract mass and want to use this formula to find SG or P. The trouble is that both SG and P are unknowns. The good news is that there is a pretty accurate equation giving SG as a function of Plato:

SG = 1 + P/(258.6-P/258.2*227.1)

The resulting quadratic equation in Plato gives 14.38 P from which I get 1.0585 SG.

By comparison, sucrose pppg is given

*somewhere around* 46. I have been using 46.214 for no good reason. This translates to 385.68 LDK - points per kg per liter.(LDK = Liter Degree per Kilogram - the metric equivalent.) Then using traditional sucrose-based gravity points, we should get

385.68*2.8725kg/20L = 55.39 gravity points for SG = 1.0534 or P = 13.66

You could do this in the Queens Measurements, but my head hurts. And Britain mostly gave up those silly units, anyway.

Assuming my math was OK it's not a

**huge** difference, but as gravity goes up, so does the gap. And that is my puzzle. Why aren't these SG and P values closer to each other? What am I missing? Did I do something bad? Is one better than the other? Are they both rough estimates and you can flip a coin.

I used to brew by knowing how many total pounds of grain my system could handle and how many ounces of hops would be tasty. If I wanted a dark beer, I would add some darker malt and less hops; light beer? maybe vary the light grains and use more hops. Mash at high or low T, depending. I never tried to estimate the OG although I would always measure it and it was always in the happy range of 1.05-1.07. Good enough for me. Hey, I even won some local competitions.

Now I have more time on my hands and am getting deeper into the weeds to learn some of the quantitative aspects of this dear hobby. Just because it is fun.