Step mash calculator
Plan your whole step mash: enter your grain and mash-in water, list your rests or pick a template like Hochkurz, and see for every rest how much boiling water to add, or how much thick mash to pull for a decoction, and how thin the mash gets.
Grain and water
Usually room temperature
Mash-in water as
= 4.12 gal
Rests· 3 · 80 min
The first rest is the mash-in. Add the rests in the order you do them.
Strike water
4.12 gal at 154.8 °F
- 140 min
Mash in · 145 °F
Mash in with 4.12 gal at 154.8 °F
Mash water 4.12 gal · 1.50 qt/lb
- 230 min
Hot water · 162 °F
Add 1.58 gal at 212 °F
Mash water 5.71 gal · 2.08 qt/lb
- 310 min
Hot water · 172 °F
Add 1.56 gal at 212 °F
Mash water 7.27 gal · 2.64 qt/lb
- Total mash water
- 7.27 gal
- Hot water after mash-in
- 3.14 gal
- Final thickness
- 2.64 qt/lb
- Total rest time
- 80 min
Runs in your browser. Nothing you enter is sent or stored.
How the infusion is calculated
The first rest is the mash-in. The planner calculates the strike water temperature from your mash-in ratio and grain temperature, assuming a preheated mash tun.
Every further rest reached with hot water is a heat balance: the heat the infusion water gives off while it cools to the new rest has to equal the heat the mash takes up while it warms to the same point. The mash is counted as its water plus the grain, which holds less heat than water: the planner uses a specific heat of 0.4 for grain, so 1 kg of grain counts like 0.4 L of water. After each infusion it adds the new water to the mash, so the next step starts from the right amount.
The hot water is boiling by default. At altitude, or if you use water from a kettle that is not quite boiling, enter its real temperature.
Ts = T₂ + (0.4 / R) × (T₂ − Tg)
V = (T₂ − T₁) × (W + 0.4 × G) / (Tw − T₂)
- Ts
- Strike water temperature
- R
- Mash-in ratio, water per grain (L/kg)
- Tg
- Grain temperature
- V
- Hot water to add (L)
- T₁
- Mash temperature before the step (°C)
- T₂
- Rest temperature to reach (°C)
- Tw
- Hot water temperature, usually boiling
- W
- Water already in the mash (L)
- G
- Grain weight (kg)
Gallons, pounds, qt/lb and °F are converted to liters, kilograms, L/kg and °C first. Heat lost to the mash tun and during the rests is not included.
Mash rest temperatures and what each one does
Each rest favors a different group of enzymes. A step mash holds the mash at one temperature, then raises it to the next, so you choose which enzymes get time to work.
With modern, well-modified malts most beers only need the two amylase rests or a single saccharification rest around 65–68 °C (149–154 °F). A beta rest at the low end gives more fermentable wort and a drier beer, an alpha rest at the high end leaves more body. Protein and acid rests are for undermodified malts, large shares of wheat, oats or rye, or traditional German schedules.
| Rest | Temperature | What it does |
|---|---|---|
| Acid rest | 35–45 °C (95–113 °F) | Phytase slowly lowers mash pH |
| Protein rest | 45–55 °C (113–131 °F) | Breaks down proteins, helps clarity with wheat and undermodified malt |
| Beta amylase rest | 60–65 °C (140–149 °F) | Produces maltose, a more fermentable, drier beer |
| Alpha amylase rest | 68–72 °C (154–162 °F) | Breaks starch into dextrins, more body |
| Mash-out | 75–78 °C (167–172 °F) | Stops enzyme activity, thinner wort for lautering |
Why each infusion needs more water
Every infusion adds water, and that water has to be heated along with the rest of the mash at the next step. At the same time, boiling water carries less spare heat the hotter the target is: at 63 °C each liter has 37 °C to give, at 78 °C only 22 °C.
Both effects stack, so a three-step infusion mash gets thin quickly. The example in the table starts at a thick 3 L/kg (about 1.4 qt/lb) and ends above 7 L/kg. The planner shows the mash water and ratio after every rest and warns you once the mash goes past 6 L/kg (2.9 qt/lb). Start thicker, switch the later rests to direct heat, or make them decoctions.
| Step | Boiling water | Ratio after |
|---|---|---|
| 52 → 63 °C | 5.1 L (1.3 gal) | 4.0 L/kg |
| 63 → 72 °C | 7.1 L (1.9 gal) | 5.4 L/kg |
| 72 → 78 °C | 7.9 L (2.1 gal) | 7.0 L/kg |
Decoction: heating with boiled mash instead of water
In a decoction you raise the temperature without adding water. Part of the mash is pulled, boiled in a separate pot and stirred back in. Because the mash does not get thinner, a decoction works where boiling water infusions run out of room, which is why traditional lager schedules use it.
Set a rest to Decoction in the planner and it shows how much thick mash to pull to reach that rest. It uses the same heat balance, assuming the decoction goes back at 98 °C (208 °F) and ignoring the water boiled off, so pull a little extra and hold some back if you get close. BrewForge recipes also let you enter the return temperature and boil-off for each decoction.
- Pull the thick part of the mash, mostly grain with little liquid. The enzymes stay in the thin mash in your tun.
- Many brewers hold the thick mash at about 70–72 °C for 10–20 minutes before boiling so it converts first.
- Boil it for 10–30 minutes and stir constantly so it does not scorch.
- Return it slowly while stirring and check the temperature. Hold some back if you are getting close to the target.
Vd = ((T₂ − T₁) × (W + 0.4 × G) + Vl × (Tr − T₂)) / (Tr − T₁)
- Vd
- Mash to pull (L)
- Tr
- Temperature of the returned decoction, 98 °C by default
- Vl
- Water boiled off in the decoction pot (L)
T₁, T₂, W and G as in the infusion formula. The planner uses Tr = 98 °C and Vl = 0.
Built into every BrewForge recipe
In BrewForge you build the mash schedule right in the recipe from infusion, temperature and decoction steps. For each step the recipe calculates the infusion water or the decoction volume to pull, tracks the water in the mash and shows the whole schedule as a mash chart.
- Infusion, temperature (direct heat) and decoction steps
- Infusion volumes, water temperatures and decoction pull volumes per step
- Mash chart with every rest, ramp and decoction
Use this calculator via API
The same calculation is also a free JSON API: no account, no key, one GET request. Handy for scripts, spreadsheets and AI assistants that should use exact brewing math instead of estimating it.
Add units=imperial (or one unit parameter per value) for °F, gallons and pounds. Every answer lists the inputs, the units and the formula it used.
GET https://brewforge.sh/api/public/calc/step-mash?grainWeight=5&rests=63:40,72:30,78:10&mashInRatio=3
FAQ
Questions & answers
How much boiling water do I need to raise my mash temperature?
It depends on how far you raise the temperature, how much water and grain are already in the mash and how close the target is to boiling. Raising 15 L of water and 5 kg of grain from 52 to 67 °C takes about 7.7 L of boiling water. Add your own rests to the planner above to get every step.
Why does every step need more water than the one before?
Each infusion adds water that also has to be heated at the next step, and boiling water gives off less heat the hotter the target rest is. Both effects grow with every step, so later infusions get larger.
How thin can a mash get?
Most brewers stay below about 4–5 L/kg (2–2.4 qt/lb). Enzymes still work in a thinner mash, but you may run out of room in the mash tun and have little water left for sparging. The calculator warns you above 6 L/kg.
Do I need a protein rest?
With modern, well-modified malts usually not, and a long protein rest can cost head retention and body. It can help with large amounts of wheat, oats or rye, or with undermodified malt. If you do one, keep it short, about 10–20 minutes.
How much mash do I pull for a decoction?
A common rule of thumb is about a third of the mash for each step. The exact amount depends on the temperature rise and on how hot the decoction still is when it goes back in. Set a rest to Decoction in the planner above to get the volume to pull from your mash water and grain weight.
Does altitude change the result?
Yes. Water boils at roughly 1 °C less for every 300 m of elevation (about 1 °F per 500 ft). Cooler boiling water carries less heat, so you need more of it. Enter your local boiling point in the hot water temperature field.
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