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Decoction Mashing

Decoction mashing is an often-misunderstood German brewing technique. I’m not going to dive into the history and tradition, but if you’d like to learn more, the most accurate and in-depth resource I have found is Braukaiser Decoction Mashing.

This will be a short walkthrough of a decoction brewday. I’m performing a Hochkurz decoction mash for a German Pilsner (see Braukaiser article for a description of different decoction schedules.) The basic outline is as follows:

63c/145f – 40 mins
-pull thick decoction at 10 mins, convert at 70c/158f, boil 10 mins, return decoction

70c/158f – 30 mins
-pull lauter (thin) decoction with 15 mins remaining, boil 10 mins, return

75c/167f – 10 mins
Begin recirculation/sparge

As you can see, the total mash time for this schedule is one hour and twenty minutes, not much more of a time commitment than a standard infusion mash, but with some of the added benefits of decoction mashing. There are some benefits to performing the more traditional, long decoction schedules, but this schedule is much less intimidating to the inexperienced decoction masher, and easier to manage, because everything is done within normal saccharification temperature range; basically, if you screw up the rests, the beer will still turn out fine.

The equipment necessary to decoct portions of the mash is simple:

-a heat source; I use a propane burner, I know others use induction burners or electric, but I like having the extra power of gas to quickly raise the temperature.

-a kettle about twice the size of the decoctions you will be pulling, for easier stirring without spills. Mine is 8 gals, to easily handle 5 or more gallon decoctions when I brew large batches.

-a ladle or strainer to remove the decoction from the mash tun. I use a large skimmer (for deep frying) like this.

-an accurate thermometer. Most decoctions require a short rest at saccharification temperature.

Well, let’s dive right in, step by step.

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Dough-in at first rest temperature

After 5 mins, I check the pH, and adjust if needed. At 10 mins, I pull the first decoction.

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I use the skimmer to remove the grain

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The grain is added to the decoction kettle

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Then mash liquid is drawn off via the MLT drain to thin the decoction

It is a fool’s errand to try and calculate a precise volume for each decoction. I just pull around 30% of the volume in the mash tun, including as much of the grain as I can skim out. This gives me more than enough decoction to move the temperature from saccharification to dextrinization; any extra is left to cool and added back slowly over the course of about 10 mins to maintain the rest mash temperature.

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I aim for a moderately thin decoction, so it's easy to stir and avoid scorching while heating. I estimate around 1 qt/lb thickness

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The decoction kettle is placed on the burner

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Speaking of stirring... always stir while the decoction is being heated

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The decoction is rested at a high saccharification temperature, in order to convert the starch. I generally turn the burner to a low flame when it reaches 68c/155f, then allow the temperature to slowly raise to 72c/162f over the course of about 10 mins

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At 10 mins, I start checking for conversion with iodine. This reaction is about 50%

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And this is almost negative. Close enough for the decoction

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After the iodine test is negative, the decoction is heated to boiling and boiled for 10 mins

I like a gentle boil, just above a simmer, for light beers. The above photo was just after the hot break/foam up, so it looks a little more vigorous than normal.

Contrary to a lot of what you’ll hear in the American homebrewing community, decoction boiling doesn’t add much color to the wort, nor does it produce a substantial amount of maillard reaction products or melanoidins, UNLESS it is specifically handled with that goal in mind.

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After the boil, the decoction is added back to the rest mash to reach the next temperature step. Any leftover decoction can be added back slowly over a few minutes, or left in the decoction kettle, if the next decoction will be pulled soon

Because this was a Hochkurz schedule, I only pulled grain from the mash tun once. The next decoction was pulled 15 mins after establishing the second rest.

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The second decoction is a lauter decoction, ie liquid only. I simply drained the mash liquid from the MLT manifold, and added it to the leftover decoction in the kettle

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Because the mash has already been sitting at 70c/158f for 15 mins, I don't worry about a conversion rest for the second decoction. It is heated straight to boiling and boiled 10 mins

That’s all the pictures I have, my photographer got bored before the job was finished, but the rest is straightforward. The lauter decoction is added back to the MLT after the boil to hit the mashout rest of 75c/167f, then recirculating and sparging proceeds as normal.

Decoction mashing isn’t for everyone, it definitely takes some thought and effort, but it is a fairly straightforward process. I like it because it gives me something to do while the main mash is converting, and I notice a more distinct malt flavor and aroma in my decoction mashed beers, as well as clearer wort to the boil kettle, less hot break, better conversion efficiency, and greater control over the body and mouthfeel of the beer.

Plus, the smell wafting through my basement as the decoction comes to the boil is absolutely HEAVENLY… and no, boiling wort doesn’t come close to comparing to boiling mash!

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The result. Prost!


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