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Decoction Mash

Decoction mashes are a traditional mash style that involves starting a mash, pulling out a portion of it (the decoction), boiling the decoction, and adding it back to the main mash. This can be performed multiple times, and each time the temperature of the overall mash steps to a new range.

A single decoction starts in the protein rest range and steps to the saccharification rest range. A double decoction starts in protein rest, steps to saccharification rest range, then steps to mash-out range. A triple decoction starts in acid rest, then protein rest, then saccharification rest, then mash-out.

Boiling the full mash would result in destruction of the amylase enzymes, which would halt starch conversion, extract tannins, and ruin the wort. But by pulling a very thick mash for the decoction, most of the enzymes remain behind in the main mash, and the pH of the decoction naturally lowers to a point where tannin extraction is not problematic.


Decoction mashing reduces hot/cold break material and lowers the mash pH. It also adds distinct flavor from caramelization and browning, different from the similar flavors produced during the wort boil.

Decoction mashes provide a complex maltiness that is unobtainable by other mash techniques. Decoction mashes are, or were, often used in the styles:

  • Pilsner,
  • Marzen
  • Bock
  • Dopplebock

How To Do It

This is a rule of thumb method:

  1. Dough in with 1.33 qt/lb @ 122F
  2. Allow grain to fully hydrate (10 minutes)
  3. Take 40% of GRAIN for decoction. Take just enough liquid for decoction to be very thick (“thick oatmeal”).
  4. Bring decoction to boil slowly, stirring often. Boil 10 - 45 minutes.
  5. Skim protein sludge off surface as it rises.
  6. Gently add decoction back to main mash. Temperature gain should be 28F.

Formula: F = ( Tf - To ) / ( 212 - Tf- K )

  • F = Ratio of grain to use for decoction
  • Tf = Desired final temperature (Fahrenheit)
  • To = Initial temperature (Fahrenheit)
  • K = Temperature loss constant. 17F if you don't know.

Length of decoction boil does not affect temperature gain, but affects maltiness character. Longer boil means more caramelization and browning, and stronger malt taste.

Scoop grain out of mash with something that drains. 1 quart container ~= 1 lb grain.

For multi-stage decoction, use these temperature guidelines:

  • 95-110 °F - acid rest
  • 120-127 °F - protein rest
  • 145-159 °F - saccharification
  • 170-178 °F - mash out


mashsparge/decoction_mash.txt · Last modified: 2017/09/11 12:10 (external edit)