Mash Infusion Calculator

Plan a step mash: the strike water for the first rest and the hot water to add for each following rest, with the water-to-grain ratio after every step.

Each step of an infusion mash needs hot water in proportion to the grain, the water already in the mash and the temperature rise. For 4.5 kg of grain mashed in at 2 L/kg, raising a 50 °C rest to 65 °C takes about 5.2 L of 96 °C water, and a further rise to 72 °C about 4.7 L.

Reviewed by Diego Santiago, Professional Brewer

MetricUSImperial (UK)

Grain (kg)

Total weight of the grain bill

Water-to-grain ratio (L/kg)

Starting ratio; keep it thick to leave room for the infusions

Grain temperature (°C)

Usually the room temperature

Infusion water temperature (°C)

Hot water for the later rests, measured as you pour

Rest 1

Rest temperature (°C)

Mash in with 9.00 L at 56.1 °C (2.00 L/kg).

Rest 2

Rest temperature (°C)

Add 5.24 L at 96.0 °C (mash now 3.16 L/kg).

Rest 3

Rest temperature (°C)

Add 4.69 L at 96.0 °C (mash now 4.21 L/kg).

Total mash water18.93LFinal water-to-grain ratio4.21L/kg

Results are estimates provided "as is," for informational and planning purposes only, without warranties of any kind. Check them before you rely on them: you are responsible for decisions about your beer and equipment, including pressure and carbonation levels, the pressure ratings of your kegs and fittings, and any alcohol content you declare. Use of this calculator is subject to our Terms and Conditions.

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How the infusions are calculated

The first rest is reached with the strike water. Each later rest is reached by adding hot water, and John Palmer’s mash infusion equation gives how much:

W_m = \frac{G\,(0.4 + R)\,(T_2 - T_1)}{T_w - T_2}

where $W_m$ is the weight of hot water to add, $G$ the weight of grain, $R$ the weight of water already in the mash divided by $G$ , $T_1$ the current mash temperature, $T_2$ the next rest temperature and $T_w$ the temperature of the infusion water. The volume to add is $W_m$ divided by the density of hot water, 0.985 kg/L. After each infusion the ratio $R$ grows, so the calculator updates it before the next step.

For example, 4.5 kg of grain mashed in at 2 L/kg for a 50 °C rest needs 9 L of strike water at about 56 °C. Raising it to 65 °C with water at 96 °C takes about 5.2 L, and a further rise to 72 °C about 4.7 L, ending at about 18.9 L of water and 4.2 L/kg.

Inside Foambyte, mash and boil profiles keep your mash steps and water-to-grain ratio, so you can reuse a step mash across recipes.

Reference table

Liters of 96 °C water per kilogram of grain for a rest step (columns), by the water-to-grain ratio before the step (rows)
Ratio \ step	40 → 50 °C	50 → 63 °C	50 → 65 °C	63 → 72 °C	65 → 72 °C
1.5 L/kg	0.41	0.75	0.92	0.71	0.56
2.0 L/kg	0.52	0.95	1.16	0.90	0.70
2.5 L/kg	0.63	1.14	1.41	1.09	0.85
3.0 L/kg	0.74	1.34	1.65	1.28	0.99
3.5 L/kg	0.85	1.54	1.89	1.46	1.14

Sources

John J. Palmer. How to Brew, Brewers Publications, 2006. Strike water and mash infusion equations, with grain at 40% of the heat capacity of water and hot water at 0.985 kg/L (chapter 16, Infusion Calculations, updated 2025); 3rd edition, online version with the author's updates.

Frequently asked questions

What is a step infusion mash?

A mash that moves through two or more temperature rests by adding hot water instead of heating the mash tun. It works in an insulated cooler, where you cannot apply heat directly.

Why does each step need more water?

Every infusion adds water, and that water has to be heated along with the grain at the next step. Raising a thin mash takes more heat than raising a thick one, so later steps need more water for the same rise.

How many rests can I do by infusion?

Usually two or three. Start with a thick mash so the tun has room for the later infusions, and check that the final ratio and volume still fit your tun and your sparge plan.

Which infusion temperature should I enter?

The temperature of the water as you pour it, which is a few degrees below boiling once it leaves the kettle. Hotter water raises the mash with less volume; water at sparge temperature works too, but takes more.

What if my mash misses a rest temperature?

Measure the actual temperature, enter it as the starting point of the next step and recalculate. The calculation ignores heat lost to the tun and the air during each rest, so real rests usually end a little cooler.