Decoction Mash Pull Calculator
Enter your mash volume and temperatures to estimate how much mash to pull, boil, and return for the next rest. The result shows the ideal heat-balance amount alongside an allowance for heat lost by the tun, transfer, and handling.
Recommended mash pull (gal)1.72
- Recommended pull percentage
- 26.53%
- Ideal pull volume (gal)
- 1.26
- Ideal pull percentage
- 19.4%
- Mash remaining in tun (gal)
- 4.78
- Extra pull for equipment loss (gal)
- 0.46
- Step feasibility
- Feasible: the loss-adjusted decoction can reach the target with less than the full mash.
Enter every temperature and the loss allowance on the selected scale; return the hot decoction gradually while stirring and measuring.
How to use this calculator
- Select US or metric units, then use that scale for every volume, temperature, and loss value.
- Enter the combined liquor and wet-grain volume in the mash tun before taking the pull.
- Use the stirred current mash temperature, the next rest temperature, and the measured return temperature of the hot decoction.
- Start with an 18°F or 10°C equipment-loss allowance, then refine it from previous brew days.
- Pull the suggested amount, then return it gradually while stirring and watching the mash temperature.
How much mash to pull for a decoction
A decoction raises the temperature of the full mash by removing a portion, heating that portion, and returning it to the tun. The pull has to carry enough heat to warm both the mash left behind and the tun system. This calculator uses the loss-adjusted approach described in the American Homebrewers Association procedure, then shows the simpler ideal heat-balance result as a comparison.
Let V be the total mash volume, Ti the current mash temperature, Ts the target rest temperature, Tb the returned decoction temperature, and X the equipment loss factor. The lossless fraction is:
Fideal = (Ts - Ti) ÷ (Tb - Ti)
The ideal pull is Videal = V × Fideal. To allow for heat lost to the tun, transfer, and the working process, the adjusted fraction is:
Fadjusted = (Ts - Ti) ÷ (Tb - Ti - X)
The recommended pull is Vpull = V × Fadjusted. The remaining mash is V - Vpull, and the extra pull allowance is Vpull - Videal. Because only temperature differences appear in the formulas, the calculation works in Fahrenheit or Celsius as long as every temperature and the loss factor use the same scale.
What changes the pull most
A larger step needs a larger pull. A hotter returned decoction needs a smaller pull, while cooling during transfer, a lower boiling temperature at elevation, and a cold mash tun all make the pull larger. The loss factor is deliberately practical rather than universal: an insulated tun, quick return, and vigorous stirring can need less allowance than a heavy vessel or a long transfer.
Using the result on brew day
Pulling a thicker portion is common because it gives the decoction a strong grain character and avoids thinning the mash, but the heat balance is still an approximation. Mix and measure the full mash before the pull. After the decoction boil, return it in portions while stirring thoroughly and stop when the whole mash reaches the rest temperature; do not treat the calculated volume as permission to overshoot.
What this calculator leaves out
The estimate assumes the pulled and remaining mash have similar effective heat capacities. It does not model mash thickness, grain distribution, tun thermal mass, boil-off during a long decoction, ambient conditions, or the changing temperature of the decoction while it is transferred. Use a prior brew's observed result to calibrate the loss factor for your system.
Worked example
Suppose a 6.50 gallon mash is at 145°F and the next rest is 158°F. The returned decoction is 212°F, and you use an 18°F loss factor. The ideal fraction is (158 - 145) ÷ (212 - 145) = 0.1940, so the ideal pull is 6.50 × 0.1940 = 1.26 gallons.
With the loss allowance, the fraction is (158 - 145) ÷ (212 - 145 - 18) = 0.2653. The recommended pull is therefore 6.50 × 0.2653 = 1.72 gallons, or 26.53% of the mash. About 4.78 gallons remain in the tun, and the loss allowance adds 0.46 gallons to the ideal pull.
Common questions
How much mash should I pull for a decoction?
Use the total mash volume, current and target temperatures, and the temperature of the returned decoction to calculate the pull. This calculator also adds an adjustable equipment-loss allowance, which usually makes the practical pull larger than the lossless heat-balance amount. Return the decoction gradually and stop based on the measured mash temperature.
Why is the adjusted pull larger than the theoretical pull?
The theoretical pull assumes every bit of decoction heat reaches the rest of the mash. In practice, the tun, spoon, kettle, transfer, and time between boiling and return absorb or lose heat. Subtracting a loss allowance from the usable temperature rise means a larger fraction must be pulled to deliver the same step.
Should I pull a thick or thin portion of the mash?
Many brewers pull a thick portion with plenty of grain, particularly for traditional decoction character and to limit the amount of thin liquor removed from the tun. A thinner pull is easier to heat and stir but can boil down quickly. Keep the mash mixed before drawing the portion so the pull represents the mash as evenly as practical.
What equipment loss factor should I use?
The AHA procedure suggests starting around 18°F, or 10°C, as an allowance. Record the actual temperature after a few steps and adjust the factor until the prediction matches your tun, kettle, transfer method, and stirring routine. Use zero only to see the idealized heat balance.
How does elevation change the decoction calculation?
Water boils below 212°F or 100°C at elevation, so the returned decoction carries less heat. Enter the temperature you actually measure at return rather than the sea-level boiling point. The calculator will increase the required pull as that return temperature falls.
Can I use this calculator for mash-out?
Yes, provided the returned decoction is hotter than the desired mash-out and the calculated pull is less than the full mash. Mash-out steps can require a substantial pull because the target is close to boiling. Return the decoction slowly and stir continuously because overshooting a mash-out is easy.