Help please with some Calculations

Looking for some help please. Perusing an 2010 sept/oct Zymurgy article focusing on "One brew day two batches."

Author is quoting Randy Moshers rule of thumb regarding partigyle.

"For instance, 5 gallons of beer at 1.090 and 5 gallons at 1.060 require (5 X 90)/(5 X 60) = 750 points. Dividing that by the total volume (10) points to a mash for 10 gallons at 1.075. His rule of thumb declares the first third of the runnings contain half of the sugar (e.g. 3 gallons at 1.125)."

Question 1. If I were to take that first third runnings of beer, and dilute to 5 gallons what would be my estimated specific gravity.


Question 2. If I were to take the last two thirds (7 gallons of preboil) of the runnings, what would be the estimated preboil gravity, and post boil at 6 gallons?

If I were to do a double batch of the Can you brew it black butte porter clone which is calculated for a 6 gallon batch.

Black Butte Porter 12 gallon recipe
21.16 lbs pale malt
2.78 lbs wheat malt
1.4 lbs crystal 80
0.84 lbs american chocolate 400l
0.84 lbs english chocolate malt 300-350l
0.84 lbs carapils

Question 3. What would be the specific gravity for the first third runnings (4 gallons). And secondly, what would be the gravity of the second 2/3's runnings.

Question 4. I want to make an strong golden ale, then add in the crystal, chocolate, and carapils malt. If I left out those grains, drew the first runnings off, then add grains to mash, stir, etc, would the second 8 gallons approximate a porter, and if not would I need to add anything else to the mash (e.g. more pale malt).

If you see anything I am missing please let me know. Thanks!

I'll see if I can run the numbers, assuming that the rules you cited are correct.

bighorn_brew said:

"For instance, 5 gallons of beer at 1.090 and 5 gallons at 1.060 require (5 X 90)/(5 X 60) = 750 points. Dividing that by the total volume (10) points to a mash for 10 gallons at 1.075. His rule of thumb declares the first third of the runnings contain half of the sugar (e.g. 3 gallons at 1.125)."

Question 1. If I were to take that first third runnings of beer, and dilute to 5 gallons what would be my estimated specific gravity.

Click to expand...

By your rule, you'll get half of the 750 points---375 points---in your first third of the wort. You then dilute to 5 gallons, so you have 375/5 = 75 ppg, or 1.075 SG. (The other way to see this is you're taking half the sugar from your 10 gallon batch and mixing it in half the volume, so it'll be the same SG.)

bighorn_brew said:

Question 2. If I were to take the last two thirds (7 gallons of preboil) of the runnings, what would be the estimated preboil gravity, and post boil at 6 gallons?

Click to expand...

You now have the other 375 points in 7 gallons, or SG=1.054. When you boil that down to 6 gallons, it's 1.063.

bighorn_brew said:

Question 3. What would be the specific gravity for the first third runnings (4 gallons). And secondly, what would be the gravity of the second 2/3's runnings.

Click to expand...

Well, calculate the total points in the recipe and follow the method above. If you're going to dilute/concentrate them to same-sized batches, then they'll both be the same SG since you have equal points in both.

If you take them at the original concentrations, then the first runnings will have twice the SG of the second (equal amounts of sugar, but twice the volume in the second runnings by your method).

bighorn_brew said:

Question 4. I want to make an strong golden ale, then add in the crystal, chocolate, and carapils malt. If I left out those grains, drew the first runnings off, then add grains to mash, stir, etc, would the second 8 gallons approximate a porter, and if not would I need to add anything else to the mash (e.g. more pale malt).

Click to expand...

I imagine this would work, but I don't have experience doing (or even thinking about) anything like this.

OK, great, you put me on the right track, I have trouble initiating math, but once shown, I can usually get by...
Thanks again!