Decoction Calculator
How much mash to pull and boil to raise the rest to your next step temperature.
How it works
Decoction mashing raises the mash temperature by removing a portion, boiling it, and stirring it back in. The hot returned mash carries the heat that lifts the whole mash to your step. The volume you need depends only on the temperature gap relative to boiling.
fraction = (target − current) / (boil − current)
pull = fraction × total mash
Sources: decoction thermal fraction as documented by Kai Troester (Braukaiser), Decoction Mashing - "decoction volume = total mash volume * (target temp - start temp) / (boil temp - start temp)". Braukaiser.com no longer serves a valid certificate, so we cite the Internet Archive snapshot (2 May 2025) of that page.
Assumes a full boil of the pulled portion and negligible heat loss. Real-world losses mean you may need a slightly larger pull - adjust as you stir back in.
Frequently asked questions
- How much mash do I pull for a decoction?
- You pull the fraction of the total mash that, once boiled and returned, supplies enough heat to raise the rest to your step temperature. That fraction is
(target − current) / (boil − current), so a bigger jump means a bigger pull. - Why is my decoction volume only an estimate?
- The formula assumes the pulled portion reaches a full boil and that heat losses to the kettle and tun are negligible. In practice mash-out losses, grain absorption and a thick-vs-thin pull all shift the real number, so treat it as a starting point and adjust to hit your target.
- Should I pull a thick or thin decoction?
- A thick (grain-heavy) decoction develops more melanoidin and malty depth but is harder to stir and scorch-prone; a thin (liquid-heavy) decoction is gentler on enzymes. This calculator gives the total volume - split it thick or thin to taste.