A decoction mash is a traditional technique used in many continental european styles. And is especially common with beers from Germany and the Czech Republic. This mashing technique comes from a time when malts were undermodified and inconsistent because temperatures could not be easily measured.

 

During decoction mashing, the brewer removes part of the thick mash (mixture of grain and very little water) and boils it. Which serves two purposes. The brewers intention for boiling the thick mash is to break down the grains which then allows the starches to become more accessible to the enzymes. This is a very important step for undermodified malts, which are malts whose cell walls are not broken down from the malting process. But it also is a tool to raise temperatures. After the boil, the brewer begins the process of adding it back to the main mash to raise the overall temperature to the next mash rest. Plus, there's another great advantage of boiling the grains because it helps with the caramelization of sugars and the production of Melanoidins for improved flavors.

 

As previously stated, decoction mashes are done in a multitude of steps. The decoction process is traditionally completed in 3 steps, but it is the brewer's decision as to how many steps they choose to incorporate. The amount of steps are based on the amount of times the thick mash is added back into the main mash and the boil is repeated, keeping in mind that the overall goal is to raise the mash temp to the subsequent rest phase. For the following example, we did a double decoction.
 

Grist Bill for 10 gallons
Original Gravity: 1.060
Final Gravity: 1.015
ABV: 5.88%
IBU: N/A
SRM: 15.24

 

8# Avangard Vienna
10# Avangard Munich
1# Briess Crystal 80
2# Avangard Wheat

 

We will split this batch into two different fermentations. Five gallons will be a amber lager using Fermentis Saflager w-34/70 and the other half will be fermented with Sweet Flemish Brett GB144. Because you know, I can't brew a beer with out my wild side coming out. So, let's get started!

 

    1. First we are going to mash-in using a water-to-grain ration of 2 quarts per pound. So that would be 21 x 2 which equals 42 quarts of water. Then, 42 / 4 is 10.5 gallons.

 

    1. Bring your mash water up to 140°F and mash-in like you normally would. Then, wait 10 minutes.

 

    1. Next, take out the thick mash for our first decoction. The ratio I was taught to use is 1 quart per pound. In our case, we will remove 21 quarts of this mash while trying to take as little wort as possible.

 

    1. Put the lid on the main mash, move the thick mash to the burner, and start bringing the temperature up. I personally like to bring the thick mash to 155°F and allow for a saccharification rest for 10 minutes.

 

    1. After that 10 minutes has elapsed you will bring the first decoction to a boil. I like to boil the first decoction for 10 minutes continuously stirring, so you do not scorch the thick mash.

 

    1. Take the decoction off the burner and introduce it back to the main mash 1 quart at a time while watching the temperature of the mash. You want to reach 145°F . Once you reach 145°F or the Beta saccharification rest, put the lid on the main mash and let it and the remaining first decoction rest for 20 minutes.

 

    1. After 20 minutes put the remaining decoction back into the main mash and stir thoroughly, and get ready to pull the last decoction.

 

    1. For the second decoction, we pull less thick mash out because we have fewer degrees to raise. I like to use a ratio of 1 quart for every 2 pounds of grain. So, we will pull 11 quarts from the mash.

 

    1. Place the second decoction on the burner and bring it to a boil. Let it boil for 10 minutes stirring continuously.

 

    1. Once again we will introduce the decoction to the main mash 1 quart at a time until our mash temp reaches 155°F. This will bring the mash up to the Alpha saccharification resting range. Allow the mash to rest for 20 minutes.

 

    1. After the rest, pull off 5 gallons of thin mash ( first runnings ) and bring it up to mash out temp or 175°F.

 

    1. Stir the thin mash back into the main mash and let it rest for several minutes.

 

    1. Sparge and boil the wort like you would any other beer.

 

BAM! You have your first decoction mash. It makes for a much longer brew day, but it's totally worth it !
 
Thanks for reading!
 
-Adam
Adam Blackard is a regular staff member at Texas Brewing Inc. who loves trying traditional techniques and is one of our best resources for information on brewing for sour fermentations and building tiny houses with compostable toilets.