As brewers, we refer to the entire process of converting the starch present in grains and adjuncts into sugar as mashing. We use the enzymes present in pale malted grains to perform this conversion. These enzymes are active over a range of temperatures, with more activity within certain ranges than outside of these ranges.
Decoction mashing is the method of boiling portions of a mash, which can extract flavors and fermentable sugars from those ingredients while allowing the remainder of the mash to “rest” (which is why it’s called a “rest mash”). When the boiled (decocted) mash is re-introduced to the rest mash, it raises the temperature of the rest mash.
When sufficient decocted mash is added back to the rest mash, the entire mash is raised from the range at which one or more enzymes are active to the range at which other enzymes are active.
Grain and Water
Decoction mashing began in the days before the development of scientific method or even simple instruments such as thermometers and hydrometers. Through trial and error and careful observation, brewers learned how to raise the temperature of a “porridge” of crushed grains and water (what we now call a mash) by boiling portions of it and re-combining it with the remainder of the mash to convert the starch in the grains into fermentable sugar.
Of course that was also before brewers knew of such things as alpha amylase, acidity, and even yeast. They just knew that if they started with a certain amount of grains and a certain amount of water and boiled a portion of it, the starchy porridge would turn sweet. Probably they would boil more of the mash in cold weather than in warm weather. It took more heat from the decocted portion of the mash to raise the temperature of the combined mash during the cold season. That’s because they were starting out with cooler water and grains, and because there was probably greater heat loss through the mash tun.
In addition, since German and other continental grains are not as completely malted (meaning not fully modified), there are portions of the barley corn that are hard and “steely” (undermodified is the technical term). These hard kernels are not as easily crushed as the remainder of the corn and not as accessible to the mashing enzymes. The decoction boil causes these areas of unconverted starch to become totally hydrated (soaked with water) and ultimately to burst, making them accessible to the mashing enzymes and increasing mash yield over a simple infusion mash.
With this perspective in mind, can you believe you have the ability, with better instrumentation and other equipment, to perform a decoction mash? Sure you can!
How does decoction mashing differ from other forms of mashing?
Infusion mashing: Infusion mashing is a process by which a measured amount of hot water of a known temperature is combined with a measured amount of crushed grains at a known temperature so that the resulting mash settles at a desired temperature. After the mash has “rested” at this temperature for a while, i.e., until conversion of starch to sugar is complete, the sweet wort is separated from the husks and other remaining matter comprising the mash.
This is the simplest form of mashing, and it differs from decoction mashing in that no part of the mash is ever boiled. Although both mashing techniques are used to convert barley starch to fermentable sugars, the process used to accomplish this goal is quite different.
Temperature program mashing (upward step infusion mashing): This is a relatively new development in the history of brewing and was specifically developed to mimic the temperature rests inherent in decoction mashing.
A temperature program mash proceeds similarly to an infusion mash; a known quantity of water at a known temperature is mixed with a known quantity of grain at a known temperature to arrive at a “rest” temperature. But instead of this temperature being in the saccharification range (142° to 158°F), it is in a range where an enzyme attacks and degrades proteins (protease) to yield a wort that is more conducive to yeast growth and resulting fermentation, as well as yielding a potentially clearer product.
The Stages of Decoction
In a decoction mash there can be a protein and a saccharification rest, but instead of applying heat to the entire mash or adding boiling water (thus thinning out the mash), part of the mash is removed to another vessel. Heat is applied to that part of the mash to raise it briefly to the saccharification temperature range, then to the boiling point. It’s held for a period of time, cooking the mash.
It’s also possible to use a decoction boil for mash-off. There’s an important distinction between the portion of the mash removed for decoction at this point and the portion removed in the earlier decoction, however. In this decoction only liquid is removed from the mash for boiling, while the first decoction called for removing the thick part of the mash (mostly grain) and leaving as much liquid behind as possible.
That’s because the mashing enzymes (alpha and beta amylase) are contained in the liquid, and for the first decoction boil they need to be left behind to perform the actual work of converting starch to sugar. At this point, when the intention is to disable the enzymes, it’s a good idea to remove just liquid. That way the bulk of the mashing enzymes are exposed to boiling temperatures, effectively denaturing them and“freezing” the character of the beer with respect to the flavor, fermentable sugars, and non-fermentable dextrins contributed by the grist bill.
Adding this liquid back to the rest mash will raise the temperature of the entire mash. The target temperature range is 168° to 170°F.
When Decoction Works Best
Decoction mashing may be used for nearly any kind of brew in which you wish to emphasize the maltiness of the beverage. Suppose you were planning a brew similar to Paulaner Salvator, a beer very malty and alcoholic. You might choose to perform a decoction mash to emphasize the malt character of this brew.
It should not be used in most English ales. These beers traditionally are brewed with a single-infusion mash, and their flavor profile reflects this. Also, as most English malt is heavily modified (meaning that it’s been fully malted), a decoction mash may inhibit proper head formation and retention because of the effects of heat on the proteins in the grain.
The Up Side
There are many reasons to choose decoction as your mash style. Here are four:
A clear advantage decoction mashing has over infusion mashing comes when undermodified grains are used. The hard tips (“steely ends”) of such grain are not typically available for conversion from starch into sugar but become gelatinized (liquefied) and available for mashing after a decoction boil. A decoction mash using undermodified grain will have a greater yield in terms of fermentable sugars than an infusion mash with the same grain.
This advantage doesn’t apply when fully-modified grains are used, because there are no undermodified portions of the ungelatinized starches present in the grain.
Another advantage is the emphasis on the maltiness of a decoction-mashed brew, described above.
Especially in a triple-decoction mash, you’ll find that the resulting beer is more likely to be clear than a similar recipe that uses an infusion mash. That’s because there’s a hot break that takes place during each decoction, which is subsequently filtered out during the sparge.
Finally, because boiled mash is used to raise the temperature of the mash from one strike temperature to another, the mash is not as thin as it can become in some temperature program mashes that use boiling water to raise the temperature of the mash. This is an advantage in two ways:
A thick mash enhances the formation of unfermentable dextrins, which aid in body and head formation and retention, versus the formation of fermentable sugars with a thin infusion mash, which yields a beer with less body.
Larger amounts of grain can be mashed using the same equipment, because less room is taken up by water in a thin mash.
A Question of Color
When the mash is heated to boiling, some of the sugars that were converted are exposed to fairly extreme heat on the bottom of the decoction pot and are carmelized, which will darken the resulting brew in proportion to the length of time the mash is boiled. Five minutes of decoction time, as recomended in the first recipe, will result in minimal darkening, even though the decocted mash will appear significantly darker than the rest mash when it’s added back after boil. This color will not carry over into the finished product.
A Word of Caution
For the brewer considering a triple-decoction mash for the first time, the task may seem nearly insurmountable. So the greatest disadvantage it presents is a perception that it’s very difficult to do. Granted, a triple-decoction mash involves many more steps than a single-infusion mash. But a single-decoction mash, when laid out in the form of a plan, isn’t much more complicated than a step-infusion mash.
In addition a brewer’s first decoction mash requires significantly more time than a single-infusion mash because of lack of experience. There are several things that could be happening at once. The experienced decoction brewer can take advantage of this and shorten the time required for a single-decoction mash to approximately the same time as a step-infusion mash.
In fact decoction mashing presents no disadvantages other than the extra time required to do the job right, and that extra amount of time will not be significant once you’ve done it a couple of times.
If you’re already doing infusion mashing, you’ll only need a little extra equipment for a decoction mash, and chances are you already have it.
Additional boiling pot for the decoction boils. For mashing five-gallon batches, this need only be a couple of gallons in size, and the bottom of it should either be heavy-gauge stainless steel or something that’s “copper-clad” such as Revere Ware.
You could use your brew pot for this, but be sure to rinse it out before you sparge into it at the end of the mash.
A strainer or slotted ladle. You’ll use this to strain the mash liquid from the grain (also called the “thick” part of the mash). You probably already have one.
A two- to four-cup measuring pitcher with handle. This is really handy in moving mash from the mash tun to the decoction boil pot and back again after the decoction boil. You can also use it to stir up the mash as you transfer decocted mash back to the mash tun, distributing the heat of the decocted portion throughout the entire mash.
If you don’t already have some, pH test papers will come in handy. If you’re already doing mashing without these, though, you can probably continue to get by.
Not a large list, is it? Now, on to the good part!
A Simple Mashing Schedule
For a single-decoction mash, we’re going to use the boiled mash to raise the temperature of the entire mash from the protein rest at 122°F to the conversion rest (also called the saccharification rest) at about 155°F.
This mash will start out very similarly to a temperature program mash, by adding hot water to crushed grain and stabilizing the temperature at the strike temperature of 122°F. At this point, we’ll deviate from the next step usually taken in a step-infusion mash.
Instead of adding additional boiling water to raise the temperature of the mash to the conversion temperature, we’ll remove a portion of the main mash, boil (decoct) it, and return it to the main mash. The higher temperature of the decocted mash will raise the temperature of the entire mash to the conversion temperature.
Pretty simple in concept, isn’t it? It’s not too much more difficult than other mashing styles in practice, and you’ll quickly decide that it’s no more difficult than handling the boiling water required to rinse the temperature of the mash in a step-infusion mash.
And now the important part: the recipe!
(Recipe for 5.5 gallons)
1.50 Hours Boil
- 4 lbs. Pilsner Malt
- 4 lbs. Munich Light
- Hopping Schedule:
- .75 oz. Perle, 9% alpha, 60 min.
- .75 oz. Tettnanger, 3.80% alpha, 40 min.
- .75 oz. Hallertau Tradition, 5.80% alpha, 40 min.
- .50 oz. Tettnanger, 3.80% alpha, 10 min.
- .50 oz. Hallertau Tradition, 5.80% alpha, 10 min.
OG: 1.040 - 1.047
FG: 1.007 - 1.012
Alcohol: 4.6-5.3% by volume
Yeast: Wyeast Bavarian (W2206)
Protein Rest: 122°F
Conversion Rest: 155°F
Add approximately two gallons of water at 129°F to the grains to hit the first strike temperature of 122°F. Hold for 15 minutes. At the end of this time, draw off about 40 percent of the mash into a separate pot, leaving as much liquid behind as possible.
While maintaining the temperature in the main mash at about 122°F, raise the temperature of the decoction mash by about 5°F per minute to 155°F, stirring constantly. The mash you moved to the decoction pot was fairly thick and dry, but there is water bound up by the starch that will be released when heated. If it is still a little dry, add additional water to make stirring easier and to help avoid scorching the grain on the bottom of the pot.
Hold the decoction mash at this temperature for five minutes, then again raise its temperature by about 5°F per minute until boiling, stirring constantly. Once the mash is boiling constant stirring is not as necessary, but stir it occasionally to make sure the entire mash is cooked thoroughly. Boil for about five minutes.
At the end of this time, remove the decoction mash from the heat. Begin adding it back to the main mash a few cups at a time, stirring thoroughly between additions to distribute the heat uniformly. When about three-quarters of the decoction mash has been added back, begin monitoring the temperature. When it reaches 155°F, discontinue adding the decoction mash back to the main mash. Set the remainder aside until it cools to about 155°F, and then add it back to the mash.
Test for conversion with iodine by placing several drops of the mash, with no visible particles of grain or husk, in a small puddle on a white porcelain dish (Corning Corelle works well and doesn’t stain) and letting it cool. Then, placing a drop of iodine into the middle of the puddle, observe any color reaction along the edge of the iodine. If you observe the colors blue or black, then there’s still starch in suspension and the mash needs to continue. However, if brown appears or there is no color change, then it’s safe to prepare for sparging.
If you’re not using a combination mash/lauter tun, transfer the mash to the lauter tun. In either case thoroughly stir the mash and let it settle for 10 minutes before initiating the sparge. Collect seven gallons of wort. You can be testing the specific gravity and tasting the sweet wort. Discontinue the sparge when the specific gravity of the runoff drops below about 1.010 or the taste reminds you of warm tea (an indication that tannins are being extracted from the husks). If this happens before you’ve collected the entire seven gallons of wort, just use plain water to make up the difference.
Boil the wort for a total of 90 minutes, adding hops per the schedule indicated. Before beginning to chill the wort, reserve two quarts of wort for later use in priming the beer. You can use sanitized mason jars for this purpose, which you’ll then store in the refrigerator.
Chill the remaining wort to about 70°F and then pitch the yeast. Transfer the fermenter to a 45°F refrigerator for three to four hours after pitching and ferment for seven to 10 days, then transfer to a secondary fermenter.
When the beer is clear (about two to three weeks), rack it to the bottling bucket into which the reserved priming wort has been poured. Bottle as usual.
Triple Decoction Bock
For the next brew, a Bock, we’ll hold the boil for a bit longer, resulting in a greater degree of darkening of the beer and a correspondingly greater degree of maltiness in the flavor profile.
We’re going to proceed to a more advanced recipe this time with a triple decoction-mashed Bock. This beer can be brewed with chocolate and crystal malts to add color and character, but we’re going to rely on three different decoctions to accomplish this. The result will be a true-to-style German Bock beer, and although the mashing schedule seems very involved, it’s no more difficult than performing a single decoction; you’re just doing it more often.
Traditional German Bock
(Recipe for 5.5 gallons)
1.50 Hours Boil
- 6.50 lbs. Pilsner
- 2 lbs. Pilsner, Toasted in 350°F oven for 15 minutes
- 4 lbs. Munich Dark
- 1 oz. Hallertau Tradition,
- 5.80% alpha, 60 min.
- .25 oz. Hallertau Tradition,
- 5.80% alpha, 20 min.
- .25 oz. Tettnanger,
- 3.80% alpha, 20 min.
OG: 1.065 - 1.073
FG: 1.008 - 1.014
Alcohol: 6.7 - 8.5% by volume
Yeast: Wyeast Bavarian (W2206)
Acid Rest: 95°F
Protein Rest: 122°F
Conversion Rest: 155°F
Note: We’ll leave some of the details out here, having already covered them in the prior recipe.
Add approximately 3 1/4 gallons of water at 99°F to hit the first strike temperature of 95°F. Hold for 15 minutes. At the end of this time, draw off about 40 percent of the mash into a separate pot, leaving as much liquid behind as possible. Maintain the temperature of the rest mash during the decoction.
Raise the temperature slowly, about 5°F per minute, to 155°F. Hold for five minutes, then raise the temperature quickly to boiling. Boil for 30 minutes, stirring occasionally. Then transfer the boiled mash to the rest mash two cups at a time, until the rest mash is at the next strike temperature, 122°F. Set any remaining decocted mash aside until it cools to 122°F, then stir it into the mash. Let the mash rest for 15 minutes, then proceed to the second decoction.
Again draw off about 40 percent of the mash, leaving behind as much liquid as possible. Raise the temperature 5°F per minute to 155°F, hold for five minutes, then raise the temperature quickly to boiling. Boil for 30 minutes. Transfer the boiled mash to the rest mash two cups at a time until the rest mash is at the next strike temperature, 155°F. Set any remaining decocted mash aside until it cools to 155°F, then stir it into the mash.
Let rest for 15 minutes, then proceed to the third decoction.
In this decoction instead of boiling the thick part of the mash, we’ll be boiling the liquid part of the mash. Draw off 40-50 percent of the liquid and bring it quickly to a boil. Hold for at least 30 minutes.
Test the rest mash for conversion with iodine as described above, then add the decocted liquid back to the rest mash until the mash-out temperature of 170°F is reached. Set any remaining liquid aside until it cools to 170°F, then stir it back into the mash.
There are two reasons we’re boiling the liquid at this point:
- That’s where the sugars reside now, so boiling the high-gravity liquid will contribute greatly to maltiness and color by caramelizing some of the sugars in the liquid.
- Since we’re no longer concerned with preserving the amylase enzymes now that conversion is complete, it’s to our advantage to disable them. That way the dextrins in the mash, which contribute to body and head retention, aren’t further converted into fermentable sugars, resulting in a thin beer.
Let the mash rest at the mash-out temperature for 10 minutes, then transfer to the lauter tun if a combination mash/lauter tun isn’t being used. In either case thoroughly stir the mash so the heavier husks settle out and form a well-stratified filter bed.
Proceed with the sparge, stopping when you’ve collected seven gallons of wort or when the specific gravity of the runoff drops below about 1.010 or the taste reminds you of warm tea (an indication that tannins are being extracted from the husks).
Boil the wort for a total of 90 minutes, adding hops per the schedule indicated. Reserve two quarts of wort for later use in priming the beer.
Chill the remaining wort to about 70°F and pitch the yeast. Transfer the fermenter to a 45°F refrigerator for three to four hours after pitching and ferment for seven to 10 days, then transfer to a secondary fermenter.
When the beer is clear (three to five weeks), rack to the bottling bucket into which the reserved priming wort has been poured. Bottle as usual.
Is It Working?
As in the single-decoction mash, when you remove the mash to be decocted it’s important to make sure that you leave as much liquid behind as possible.
With the exception of the last decoction, you’ll again observe that the mash becomes much more liquid after a brief stop at 155°F.
The last decoction, since it involves a high-gravity liquid, is likely to boil over unless you maintain strict control of the heat, just as any wort boil is subject to boiling over.
As mentioned before, some of the sugars that were converted during the brief conversion time in the decoction boil are caramelized, which will darken the resulting brew in proportion to the length of time the mash is boiled. Thirty minutes of boiling time will result in noticeable darkening, and significant additional maltiness will be contributed to the resulting beer.
A Final Note
If you decide to perform decoction mashing in a future brew, do yourself a big favor: don’t pass judgment on how much longer it takes to mash this way versus the infusion mash. Just like everything, it takes practice to learn how to do the mash efficiently and performing more than one task concurrently. By overlapping tasks you can shorten the time required to mash in this manner, and a single-decoction mash shouldn’t take any longer than a temperature program mash.
So... give it a try!