How to Do a Decoction Mash

If you’ve been wondering how to do a decoction mash, you’ve come to the right place. This practice has been in place for darker, richer beers for centuries if not millennia. It’s relatively simple, if labor intensive, and many brewers will swear by it.

Beer Mash

The first step to a decoction mash is to understand the mash process in general. For those still new to brewing, the mash-in is the step when the grains, or grist, are steeped in hot water to extract the starches and sugars.

Today, most brewers simply add hot water to the grist, allow the wort to steep for 45 to 60 minutes, and then enter the sparging process, where the grains are strained and rinsed for runoff.

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Some brewers will perform a step mash, or a step infusion mash, wherein the mash temperature is raised and then allowed to rest once or twice. Some brewers will also add boiling water to the mash once or twice, allowing it time to rest in between additions.

The thinking here is that with each temperature raise and rest, enzymatic processes are thickening the mash, breaking down the proteins and glucans, and making the sugars easier to extract.

Increasing the temperature gradually and then allowing a rest ensures the grains never get scorched or overcooked and mushy.

How to Do a Decoction Mash

A decoction mash follows many of these same processes and adheres to the same philosophy with a single difference.

Instead of raising the temperature of the entire mash, one third of the thickest part of the mash is removed from the total mash, placed in a separate vessel, and boiled for anywhere from 10 to 40 minutes. Then, the “decocted” mash is returned to the original batch and allowed to rest for anywhere from 15 to 45 minutes.

Have you optimized grain sugar extraction? Test it out with our Mash Efficiency Calculator!

Brewers who still engage in decoction mashing, largely those in smaller regions in Germany and the Czech Republic, swear by the process and insist it creates characteristics in the beer that cannot be imitated through any other process.

To perform decoction mash, simply complete all the other steps of brewing:

Choose your malted grain, grind it, and steep it in hot water, usually around 122 degrees F.

Then, after a period of rest, remove one third of the grist with enough water to still cover the top, and place it in another vessel. Bring the decocted mash to a boil, around 122 degrees F, and stir it constantly for as long as you decide to boil it. Note that you also have to keep an eye on your original mash.

Then, when you’re done boiling, return the decocted mash to the original mash and allow a rest period up to an hour.

To do a double decoction mash, or a triple decoction mash, you’ll repeat these steps, but you’ll increase the temperature by about 20 degrees Fahrenheit each time, remaining consistent with your boil and rest times.

The first rest is known as the acid rest, where you can check your pH levels and perform any adjustments necessary.

The second rest is your protein rest, where your proteins will allow your enzymes to uncoil and get to work.

The third rest is the saccharification rest, where the sugars become fully extracted for fermentation.

After your final rest, you can mash out and sparge, deciding if you want to include your runoff on the original wort or create a small beer.

Is Decoction Mash Necessary?

The next question is always whether or not a decoction mash is even necessary.

This question remains up for debate.

Several brewers will agree that even if you don’t need a decoction mash to enhance the character of your beer, it does increase efficiency. This makes sense as you are basically steeping the mash multiple times, stirring way more than you would ordinarily, and boiling longer and higher than you would normally.

Still, with all the modified malts on the market today, plenty of brewers will argue that you can simply choose specialty malts for the same effects.

As with most crafty and creative elements, you will have to decide for yourself which side you agree with.

Experience and experimentation are key.

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