Mash Step Infusion Calculator (Boiling Water Addition)

How it works

Infusion (L) = (T target − T current) × (0.41 × grain kg + water L) ÷ (T infusion − T target)

Step mashing raises the grain bed through two or more rests — a protein rest around 50 °C, saccharification at 62–70 °C, mash-out at 76–78 °C — and in a simple insulated tun the only way to add heat is to add hot water. The equation is a heat balance: the mash (grain at 0.41 relative heat capacity plus its water) must gain enough energy to reach the target, and the infusion water supplies it as it cools from its own temperature to that same target. Because each step dilutes the mash, brewers plan the first rest thick (around 2–2.5 L/kg) so there is room for later additions. Mash-out is the step that most often runs out of room, which is why many switch to direct heating or a sparge at 76 °C instead.

Worked example

5.5 kg of grain in 15.4 L at 66 °C, raising to 76 °C with 99 °C water: 10 × (2.26 + 15.4) / 23 = 7.7 L — the ratio rises to 4.2 L/kg.

Frequently asked questions