Strike water temperature

Calculate how hot to heat your mash water so that adding grain at room temperature lands you at the target mash temperature.

Formula

Strike_T = (0.41 × (T_target − T_grain) ÷ R) + T_target
where R = water-to-grain ratio (L water per kg grain), and 0.41 is the heat-capacity ratio between water and grain.

Inputs

Name	Unit	Description
T_target	°C	Desired mash temperature
T_grain	°C	Temperature of dry grain (room ambient)
R	L/kg	Water-to-grain ratio (typical 3.0 L/kg)

Outputs

Name	Unit	Description
T_strike	°C	Temperature to heat the strike water to before adding grain

Worked example

Inputs:

T_target = 67
T_grain = 18
R = 3

Calculation:

T_strike = (0.41 × (67 − 18) ÷ 3.0) + 67 = (0.41 × 49 ÷ 3.0) + 67 = 6.7 + 67 = 73.7

Result:

Heat water to ~74 °C; mash will land at 67 °C after grain addition

Sample values

Grain temp °C	Mash target °C	Ratio L/kg	Strike temp °C
18	65	3	71.4
18	66	3	72.6
18	67	3	73.7
18	68	3	74.8
18	65	2.5	72.2
10	67	3	74.8

What this assumes

The 0.41 multiplier is an empirical heat-capacity ratio that combines:

The specific heat of grain (~0.4 cal/g·°C) vs water (1.0 cal/g·°C)
The thermal mass of the mash tun walls
Typical heat loss during the strike-and-stir minute

If your mash tun is cold (e.g. a stainless kettle on a chilly day) you may need to preheat it with hot water and dump, or add 1-2 °C to the strike temperature.

Sources of error

Mash tun preheat — a cold mash tun absorbs heat from the strike water before grain ever enters. Preheat by filling with 70 °C water for 5 minutes, then dump.
Grain temperature — winter garages can have grain at 5-10 °C. Adjust grain temp upward in summer.
Stirring — under-mixed mash has hot pockets and cold pockets; the thermometer reading is misleading. Stir thoroughly.

If your first mash misses target by 2 °C, you can correct in the tun: add small amounts of boiling water to raise temperature, or stir vigorously and lid-off to drop it.