Mash Water Calculator

In short Two questions on brew day: how hot the strike water needs to be, and how much water the whole thing takes. The first is a heat balance rather than a lookup. Cold grain cools the water by exactly as much heat as the grain gains, and grain holds roughly 0.4 times as much heat per kilo per degree as water does. Rearrange that and the strike temperature falls out: at 3 litres per kilo, mashing 20°C grain to 66°C needs water at about 72°C. THICKER MASHES NEED HOTTER STRIKE WATER, which catches people out because the units run the other way: thickness is quoted in litres per kilo, so FEWER litres is the thicker mash, and less water carrying the heat has to start further above the target. The water accounting is the part that goes wrong more often. Grain keeps roughly a litre per kilo and never gives it back, which on a five-kilo bill is five litres gone before the boil starts. The boil takes another few litres an hour. Work backwards from what you want in the fermenter: add the boil-off to get the pre-boil volume, subtract what comes out of the mash tun, and the remainder is your sparge. A five-kilo mash at 3 L/kg for a 19-litre batch takes about 15 litres of mash water and 12 of sparge, and 27 litres of water in total for 19 litres of beer. Two things this calculation cannot see. The mash tun itself absorbs heat, and a cold one easily takes two or three degrees off the strike temperature — rinse it with boiling water first, or add a couple of degrees and stir well, and always read the mash a minute after stirring rather than the instant the water lands. And grain specific heat, absorption and boil-off are all approximations that vary with your equipment and your crush. Measure your own boil-off once, over a real hour with a real lid position, and this page stops being accurate in general and starts being accurate for your kit — which is the only kind of accuracy that helps on a brew day.