Parti-Gyle Blending Calculator
Enter the measured volume and gravity of each running to split a parti-gyle mash into a target beer and the beer left behind. The calculator shows the blend, the remaining wort, and the estimated post-boil gravity for each kettle.
First runnings for target beer (gal)2.78
- Second runnings for target beer (gal)
- 2.22
- First runnings left for second beer (gal)
- 1.22
- Second runnings left for second beer (gal)
- 3.78
- Second beer pre-boil volume (gal)
- 5
- Second beer pre-boil gravity
- 1.046 SG
- Target beer predicted post-boil volume (gal)
- 4
- Target beer predicted original gravity
- 1.075 SG
- Second beer predicted post-boil volume (gal)
- 4
- Second beer predicted original gravity
- 1.057 SG
- Blend feasibility
- Feasible: the target blend can be made from the available runnings, with wort left for a second beer.
Pre-boil and post-boil beers
| Beer | Pre-boil volume (gal) | Pre-boil gravity | Post-boil volume (gal) | Predicted OG |
|---|---|---|---|---|
| Target beer | 5 | 1.060 SG | 4 | 1.075 SG |
| Second beer | 5 | 1.046 SG | 4 | 1.057 SG |
Volume outputs use US gallons throughout.
Post-boil estimates apply the same boil-off rate and boil time to each kettle.
How to use this calculator
- Measure the collected first and second runnings and enter their volumes and corrected specific gravities.
- Enter the target beer pre-boil volume and gravity you want in the main kettle.
- Enter the boil-off rate and boil time you expect for each kettle.
- Read the running allocation first, then check the feasibility message before brewing to the numbers.
How the parti-gyle blend is calculated
Parti-gyle brewing separates stronger first runnings from weaker later runnings, then blends them into two or more beers. This calculator starts after collection, when both running volumes and gravities have been measured. It answers the brew-day blending question: how much of each running should go into the target beer, and what beer remains from the unused wort?
The calculation uses gravity points, the practical brewer's shorthand for specific gravity above 1.000:
P = 1000 × (SG - 1)
Let Vs and Vw be the available strong and weak running volumes. Let Ps, Pw, and Pt be the gravity points for the strong running, weak running, and target beer. Let Vt be the target pre-boil volume. The strong-wort allocation is:
x = Vt × (Pt - Pw) ÷ (Ps - Pw)
The weak-wort allocation is:
y = Vt - x
The remaining first and second runnings are Vs - x and Vw - y. The second beer's pre-boil gravity points are the leftover gravity-point inventory divided by the leftover volume:
Pr = ((Vs - x) × Ps + (Vw - y) × Pw) ÷ ((Vs - x) + (Vw - y))
Specific gravity is then 1 + P ÷ 1000.
Post-boil estimates
Boil-off concentrates the same gravity points into a smaller volume. If b is boil-off per hour and t is minutes, the boil-off volume is B = b × (t ÷ 60). Target post-boil gravity uses 1 + (Vt × Pt ÷ (Vt - B)) ÷ 1000. The second beer uses the same concentration step with its leftover pre-boil volume and points.
What moves the result most
The target gravity's position between the two runnings decides the blend. A target close to the first runnings uses mostly strong wort; a target close to the second runnings uses mostly weak wort. Available volume matters just as much: a mathematically correct blend is not brewable if it requires more first or second runnings than you collected.
What this calculator leaves out
This tool does not predict mash conversion, lauter efficiency, future sparge gravity, trub loss, hop absorption, transfer loss, late sugar additions, or cooling shrinkage. It assumes both volumes use the same hot- or cold-volume basis and that hydrometer or refractometer readings have already been corrected.
Worked example
Suppose you collected 4.00 gallons of first runnings at 1.080 SG and 6.00 gallons of second runnings at 1.035 SG. You want 5.00 gallons of target wort at 1.060 SG, with a 1.00 gallon per hour boil-off rate and a 60 minute boil.
The first running has 80 points, the second has 35 points, and the target has 60 points. The strong-wort allocation is 5 × (60 - 35) ÷ (80 - 35) = 2.78 gallons. The weak-wort allocation is 5 - 2.78 = 2.22 gallons.
That leaves 1.22 gallons of first runnings and 3.78 gallons of second runnings for the second beer. The leftover wort is 5.00 gallons at about 1.046 SG. After a 1.00 gallon boil-off, the target beer is estimated at 4.00 gallons and 1.075 OG, while the second beer is estimated at 4.00 gallons and 1.058 OG.
Common questions
How do I split first and second runnings for a parti-gyle brew?
Measure the volume and gravity of each collected running first. Choose the target beer volume and gravity, then use gravity-point blending to calculate how much strong and weak wort belongs in that kettle. The remaining wort becomes the starting point for the second beer.
Can I hit a target gravity by blending two worts?
Yes, if the target gravity sits between the two measured wort gravities and you have enough of each running. If the target is stronger than the first runnings or weaker than the second runnings, blending those two worts cannot reach it without adding sugar, water, or another wort.
What gravity will the leftover small beer have?
The leftover beer gravity is the remaining gravity-point inventory divided by the remaining volume. Strong leftover wort raises it, weak leftover wort lowers it, and a target blend that consumes all wort leaves no second beer to estimate.
Should I use pre-boil or post-boil gravity?
Use pre-boil gravity for the blend itself because that is the wort you are dividing between kettles. The post-boil original gravity is a concentration estimate after boil-off, so it is shown separately from the blending target.
Can I use liters instead of gallons?
Yes. Select liters and enter every volume in liters, including boil-off per hour. The formulas are ratio-based, so they work the same way as long as every volume uses the same unit system.
What should I do when the requested blend is not feasible?
Use the feasibility message to see what failed. You may need to lower or raise the target gravity, change the target volume, collect more of one running, reduce boil-off, or accept that the remaining second beer will be smaller than planned.