Calculator
Strike water temperature calculator
How hot should my mash water be?
Strike water is heated above the target mash temperature because the grain is cold and will pull heat out the moment the two meet. How far above depends on the grain's temperature, the ratio of water to grain, and the specific heat of malt relative to water.
Mash temperature is worth this care because it determines the balance between the two enzymes converting starch to sugar. A mash a few degrees cooler favours beta-amylase and produces a more fermentable wort and a drier beer; a few degrees warmer favours alpha-amylase and leaves more unfermentable sugar and a fuller body. This calculation ignores heat lost to the vessel itself, which is real and specific to your equipment — most brewers add a degree or two from experience.
Result
- Strike water temperature73°C
- Water needed13.8 L
- Strike temperature163°F
Working
Strike temp = (0.4 ÷ R) × (T − G) + T
| Step | Expression | Value |
|---|---|---|
| Temperature rise needed | T − G | 46 °C |
| Heat capacity ratio | 0.4 ÷ R | 0.1455 |
| Strike temperature | (0.4 ÷ R) × (T − G) + T | 72.7 °C |
| Water volume | 5 kg × 2.75 L/kg | 13.8 L |
What it means
Mash temperature is the main lever on fermentability: around 64 °C produces a drier beer, around 68 °C a fuller-bodied one, from the same grist.
Worked example
The example above starts from these values. It is rendered on the server, so the formula, assumptions and limitations are all present whether or not you change anything.
- Result73°C
- Water needed13.8 L
- Strike temperature163°F
Inputs
| Grain weight | 5 kg |
|---|---|
| Grain temperature | 20°C |
| Target mash temperature | 66°C |
| Water to grain ratio | 2.8 L |
How it is calculated
Strike temp = (0.4 ÷ R) × (T − G) + T
What each term means
| R | Water-to-grain ratio in litres per kilogram |
|---|---|
| T | Target mash temperature |
| G | Grain temperature before mashing in |
| 0.4 | Specific heat of grain relative to water |
Step by step
| Step | Expression | Value |
|---|---|---|
| Temperature rise needed | T − G | 46 °C |
| Heat capacity ratio | 0.4 ÷ R | 0.1455 |
| Strike temperature | (0.4 ÷ R) × (T − G) + T | 72.7 °C |
| Water volume | 5 kg × 2.75 L/kg | 13.8 L |
What this assumes
- The mash tun is preheated. A cold vessel will absorb heat and undershoot the target, often by several degrees.
- Grain is at the stated temperature throughout, not just on the surface of the sack.
Where it stops being reliable
- Does not account for heat lost to the vessel, which varies enormously between an insulated cooler and a bare metal pot.
- The 0.4 heat-capacity ratio is a single figure standing in for a property that rises with the grain’s moisture content, and the underlying measurement carries about 8% error — worth roughly half a degree on a typical mash, which is smaller than the vessel loss above.
- Best treated as a starting point calibrated against your own equipment over a few brews.
What the number means
Mash temperature is the main lever on fermentability: around 64 °C produces a drier beer, around 68 °C a fuller-bodied one, from the same grist.
Empirical approximation. A curve fitted to measured data. It has real error bars, and it is frequently quoted as though it were exact.
Sources: The 0.4 ratio is checked against measured barley specific heat in Łapczyńska-Kordon et al., Int. Agrophysics 8:271–275 (1994), Table 1: c = 33.107w + 1569.28 J/kg·K. At the 4–5% moisture of kilned malt that is about 0.41 of water’s specific heat.