What is parti-gyle brewing?

Parti-gyle is the historic technique of drawing several separate worts from a single large mash. The first runnings are strong and become a big beer like a barleywine, while the weaker later runnings become a small or table beer. It maximises grain use from one mash.

How is each runnings' gravity calculated?

The grain yields a fixed pool of extract, measured in gravity-points times gallons. The tool distributes that pool across the runnings using a declining-extraction model where each successive draw pulls about 60 percent of the sugar still remaining, then divides each runnings' captured points by its volume to get its gravity.

Is the total extract conserved?

Yes. The sum of points times volume across all runnings exactly equals the total pool you set, because the final runnings is assigned whatever sugar is left. Blending all the runnings back together reproduces your reference gravity.

How strong is the first runnings versus the last?

The first runnings is by far the strongest, often roughly twice the blended average, while a second runnings is much weaker and a third weaker still. The exact ratio depends on grain bed efficiency, but the declining pattern is consistent and is what makes parti-gyle useful for brewing two very different beers.

Can I model three beers from one mash?

Yes. Add up to four runnings rows in draw order. The calculator splits the sugar across all of them and shows each gravity, so you can plan a strong ale, a session beer, and a small beer from the same grain bill.

Parti-Gyle Gravity Calculator

Parti-gyle is one of brewing’s oldest tricks: a single big mash drained into several separate worts, each progressively weaker, so one grain bill yields two or three very different beers. This calculator predicts the gravity of each runnings so you can plan the strong beer and the small beer before you brew.

How it works

The grain yields a fixed amount of sugar, which we track as a pool of gravity-points-gallons: an SG of 1.050 is 50 points, and multiplying points by gallons gives a conserved total. You set this pool by entering the gravity your full mash would reach if every runnings were blended together, along with the total volume.

The tool then distributes that pool across your runnings in draw order using a declining-extraction model. Each successive draw pulls roughly 60% of the sugar still left in the grain bed, which mirrors how sparge efficiency falls off:

points captured by a runnings = (remaining sugar) × extraction fraction

The final runnings receives whatever sugar is left, so the total is conserved exactly. Each runnings’ gravity is then its captured points divided by its volume.

Worked example

Suppose your full mash would make 6 gallons at 1.090 (90 points). That is a pool of 540 point-gallons. Drawing two 3-gallon runnings:

First runnings takes about 60% of the pool — roughly 324 point-gallons over 3 gallons, near 1.108: a strong barleywine wort.
Second runnings takes the remaining 216 point-gallons over 3 gallons, near 1.072: still a solid beer.

Blending both back together returns the original 1.090.

Tips and notes

Add up to four runnings in draw order to plan three beers from one mash — for example a strong old ale, a bitter, and a small beer. Remember that the first runnings is far stronger than the average, so size your fermenter and hop bill accordingly. Real efficiency varies with crush, mash thickness, and sparge technique, so treat these as planning figures and confirm with a hydrometer. All calculation runs locally in your browser.