How hot should the strike water be?
Enter the grain, the water ratio and the mash temperature you want: get the water temperature, or how much hot water raises a mash that is too cool.
Palmer suggests starting a multi-rest mash in a cooler stiff, at 0.75 to 1 quart per pound, to leave room for the water you add later. Thinner mashes need cooler water.
What the strike water temperature means
Strike water is the hot water you pour over the crushed grain at the start of the mash. The enzymes in the malt convert starch to sugar in a narrow range of temperature, so the aim is to have the whole mash settle at one value, usually somewhere between 148 and 156 °F, within a minute or two of mixing. The water has to start hotter than that, because the dry grain is cold and the tun absorbs heat; how much hotter depends on how much water there is per pound of grain.
The two equations
This page uses the equations in John Palmer's How to Brew, chapter 16, section "Calculations for Boiling Water Additions". The initial infusion needs only the ratio, because the weight of the grain cancels out when you mix hot water with dry grain:
Tw = (0.2 ÷ r)(T2 − T1) + T2, with Tw the water temperature, r quarts of water per pound of grain, T1 the grain temperature and T2 the mash temperature you want.
Raising a mash that is already mixed needs the grain as well, since the grain now holds heat too:
Wa = (T2 − T1)(0.2G + Wm) ÷ (Tw − T2), with Wa the quarts of water to add, G the pounds of grain, Wm the quarts of water in the mash, T1 the present and T2 the target mash temperature, and Tw the temperature of the water you add.
Worked example: 10 pounds of grain at 70 °F, 1.5 quarts per pound, 152 °F target. Tw = (0.2 ÷ 1.5) × (152 − 70) + 152 = 162.9 °F. Palmer's own multi-rest example, 8 pounds of grain taken from 70 °F to 104, 140 and 158 °F with water at 210 °F, needs water at 110.8 °F for the first rest, then 4.94 and 5.03 quarts for the next two, 18.0 quarts in all.
Limits of the method
It is a simplified heat balance. Palmer says the constants are rounded to single digits and that the equation assumes no heat is lost to the surroundings. He recommends preheating the tun to reduce that error and reports that the equation is "fairly reliable and consistent batch-to-batch". It does not model the heat capacity of a particular cooler, kettle or mash paddle.
The 0.2 is an effective constant. It stands for the heat capacity of grain compared with water, combined with the weight of a quart of water. We read it that way ourselves; Palmer does not explain the number. In metric units it becomes 0.41 (liters and kilograms), the value he gives.
Palmer's example contains an arithmetic slip. For the third step he writes 18 × 15.1 ÷ 52 = 5.2 quarts, but 0.2G + Wm is 1.6 + 12.9 = 14.5, which gives 5.03 quarts. The calculator follows the formula.
Water cannot be hotter than boiling. At high altitude water boils below 212 °F (100 °C), which caps how much heat each quart can carry; the calculator warns when the hot water you enter is above the boiling point at sea level.
Frequently asked questions
How hot should the strike water be?
Hotter than the temperature you want the mash to settle at, because the cool grain and the mash tun take heat out of the water. John Palmer's equation is Tw = (0.2 ÷ r)(T2 − T1) + T2, where r is quarts of water per pound of grain, T1 the temperature of the dry grain and T2 the mash temperature you are aiming for. For 70 °F grain, a 152 °F mash and 1.5 quarts per pound the water goes in at 162.9 °F. A thicker mash (less water per pound) needs hotter water, a thinner one cooler water.
How do I raise the temperature of a mash with hot water?
Palmer's infusion equation is Wa = (T2 − T1)(0.2G + Wm) ÷ (Tw − T2). G is the pounds of grain, Wm the quarts of water already in the mash, T1 the present temperature, T2 the target and Tw the temperature of the water you add. His own example is 8 pounds of grain with 16 quarts of water (2 quarts per pound), raised from 150 °F to 158 °F with 210 °F water: about 2.7 quarts, which agrees with his "approximately 2.7 quarts". Palmer notes that the water need not be boiling; sparge water at 170 °F works, but more of it is needed.
What changes in metric?
Palmer writes that the equations work for degrees Celsius, liters and kilograms, with one change: the constant 0.2 becomes 0.41. The ratio r is then liters per kilogram. For 21 °C grain, a 67 °C mash and 3.13 L/kg, which is the same thickness as 1.5 quarts per pound, the water is 73.0 °C, or 163.4 °F, against 163.6 °F in US units: the two constants agree to within a degree or so. Our own check is that 0.2 × 2.0864 (liters per kilogram in one quart per pound) is 0.417, so Palmer's 0.41 is a rounded value.
Why does my mash come out a few degrees off?
The equation is a simplified heat balance. Palmer says it assumes that no heat is lost to the surroundings and that the constants were rounded to single digits, which in his experience changes the answer by at most a cup of hot water and less than 1 °F. A cold cooler or kettle breaks the first assumption: it soaks up heat until it matches the mash. Pour some hot water into the tun a few minutes before dough-in, tip it out, and your mash will land closer to the number. The temperature of the grain also matters; grain stored in a cold garage is not at room temperature, so measure it.
Can I plan several rests in one go?
Yes, use the Schedule tab. It follows Palmer's example for a three-rest mash, 8 pounds of grain from 70 °F to 104, 140 and 158 °F with 1 quart per pound at the start and 210 °F water for the later steps. The first water is 110.8 °F (Palmer: 110.8, rounded to 111). The infusion steps need 4.94 and 5.03 quarts, 18.0 quarts in all and a final ratio of 2.25 quarts per pound. Palmer prints 5.2 quarts for the last step; his arithmetic there is off (0.2G + Wm is 1.6 + 12.9 = 14.5, not 15.1), and the formula gives 5.03. The calculator uses the formula. Each step needs more water than the one before, which is why multi-rest mashing in a cooler is practical only for two or three rests.
Sources: John Palmer, How to Brew (free online edition, howtobrew.com), chapter 16 "The Methods of Mashing": "Calculations for Boiling Water Additions" and "Multi-Rest Mashing" (first edition, copy at web.archive.org, read October 28, 2026). The newer fourth edition of the book was not opened. Neighbours: ABV calculator, priming sugar calculator, yeast pitch rate calculator. How we check our calculators.