The Decoction Mash

Decoction mashing has both a mystic and feared quality to it. Purists imagine achieving perfection in the ultimate Bavarian or Bohemian lager. The more pragmatic of us fear the time-intensive triple decoction with its grueling brew day and extended mess. Like most things, the truth lies somewhere in the middle. Decoction mashing is not done without cost, but it can also add a unique character to beer that is difficult to replicate with any other method.

The foundation of the decoction technique is not hard to understand. It is a method for heating your mash by extracting a portion of the wort and grains from the mash and bringing them to a boil in a second vessel. The boiling mixture is then added back to the mash to raise the temperature of the mash as a whole. It is most often done as part of a multi-step mash, with decoction used for each step after the first. By varying the portion you pull off and boil you can accurately control the temperature for each step.

Decoction is most closely associated with European lagers, though it can also be done with ales. In particular, many of the Bavarian and Bohemian beer styles were traditionally made using decoction, though the practice spread to other breweries around the world.

The decoction method provides a rich, bready maltiness beer drinkers closely associate with German lagers, and also excellent wort clarity that likely aided in development of the first light-colored lagers. There are some additional technical benefits that we’ll cover in more detail shortly. The downside of decoction is mainly in terms of time. It takes substantially longer than a simple infusion mash, especially if you want to perform the traditional triple decoction mash. 

History of Decoction 

Decoction has its roots in ancient brewing techniques. While it’s hard for many of us to imagine life before cell phones, the thermometer is a fairly recent invention, as is modern brewing science. Daniel Fahrenheit invented the alcohol thermometer in 1709, but it was not widely used until much later. Similarly we had little scientific understanding of the subtleties of the malting process, mash enzymes, or what temperature ranges were best for mashing. As a result, the malts used were often undermodified (lacking the digestion of cell walls during germination) and the mash process itself involved a lot of convoluted steps.

Going back to medieval times, Mika Laitinen’s recent book Viking Age Brew: The Craft of Brewing Sahti Farmhouse Ale describes the ancient farmhouse process of brewing beer. Beer was made locally, with local ingredients, usually in the same location it was consumed. It was mashed in wooden vessels, as metal was expensive and often rare. Hot stones were added from the fire to a wooden mash tun to heat the water and grain. 

Since neither the temperature nor process was well understood, the mash temperature would slowly be raised by adding more stones over a period of hours until it reached boiling, and there was no separate boil stage. This long process had advantages for converting the often undermodified malts as lower temperature stages allowed time for cell wall digestion and phosphate release needed for sugar conversion. The wort was then lautered, often over a filter bed with herbs or spices to infuse flavor, and then fermented either open or with reharvested yeast.

As brewing moved from home to commercial settings, a dizzying variety of mash techniques were developed. Most were quite complex by modern standards, as brewers struggled to make enough fermentable sugars to produce good beer. Georges Lacambre describes in his 1851 book, Traité Complet de la Fabrication des Bières, some insanely convoluted Belgian brewing practices of the time involving five vessels, baskets, pans, strainers and “eight to ten strong brewers” to manage the whole process. Multi-step mashes, perhaps derived from the ancient mash process, were quite common though the method for heating and boiling the wort had evolved.

Unfortunately I could not find a definitive time or location for the invention of decoction mashing. The technique became commercially popular in Bavaria and Bohemia regions, but most of the techniques we now recognize as “traditional” decoction techniques were likely developed in the 1800’s. Pilsner Urquell is the first brewery cited to use decoction methods, and it was established around 1840. The great German breweries we associate with decoction were all established after that date.

Though the lack of thermometers and well-modified malt are often cited as a reason behind decoction, very likely the momentum of “tradition” played a larger role. In fact, by the 1800s both well-modified malts and thermometers were available. The significant advantage of decoction mashing is that it provided a very repeatable process to achieve a multi-step mash at precise temperatures and also it was simpler than some of the convoluted multi-step mash procedures that preceded it. Also as the technique was perfected, it resulted in highly fermentable wort of improved clarity, which was critical for the development of the lighter-colored European lager styles it is so closely associated with. Light lagers were also a mid-1800s invention, as darker ales dominated commercial beer production prior to that date.

In examining the history of decoction mashing, it is indeed hard to separate the technique from the development of lightly-colored lagers. Pilsner Urquell, released in 1842, is widely cited as the first commercial pale lager, though many dark lager styles predate it. It was followed quickly by the release of a wide number of lager styles we associate with Bavaria and Bohemia. By 1870, lagers made up 97.9% of the production in Bohemia.1 With the development of rail transportation and refrigeration, the light lager craze spread across the globe, becoming the most popular beer style worldwide in the late 1800s. Despite the American craft beer revolution, Pilsner is still the dominant beer style by a wide margin both inside and outside the US.

The Advantages and Disadvantages of Decoction

Before we dive into the fine details of decoction mashing, let’s discuss some of the advantages and disadvantages of decoction. First, we need to acknowledge that decoction mashing breaks some of the modern fundamental rules of mashing. Yet, breaking these rules turns out to also
be a key to the method’s success.

For example, when I learned all-grain brewing, I was taught to never raise the temperature of the mash above 178 °F (81 °C) or I would risk extracting tannins. However, decoction does exactly that — in fact it brings a portion of the mash to a boil multiple times! How can this be? Well it turns out that temperature is not the critical factor driving tannin extraction and in fact the pH, particularly during the sparge, drives most of the excess tannin extraction. The pH in a decoction mash does not rise high enough to promote excessive extraction of tannins.

The other obvious oddity is direct heating of the decoction itself. Most homebrewing systems are designed to avoid directly heating the mash tun to avoid scorching or darkening the grains. Instead they use infusions of hot water heated separately or a recirculation method to avoid directly heating the grains. However, in decoction we extract a portion of the mash to a separate vessel and bring it to a full boil with direct heat. This does risk scorching the grains, so care must be taken to constantly stir the decoction, however this direct heating is also responsible for developing much of the malty character we associate with decoction.

A unique malty finish to the beer is a critical advantage of decoction. While single-infusion mash brewers often attempt to replicate this effect using melanoidin malt, it is difficult to achieve the exact decoction flavor. Directly heating a portion of the grains to boiling creates melanoidins, which are a major color/flavor compound in the malts via a Maillard reaction. This slightly darkens the malt but also produces a slightly higher content of high molecular weight polymers that contribute maltiness and body to the finished beer. Munich malts, which are a large part of the grain bill for many Bavarian beer styles, have a high melanoidin content that is enhanced by decoction.

Boiling a portion of the mash also helps to break down the cellular walls in the grains. This releases additional enzymes and substrates from the endosperm into the mash, which generally results in slightly higher overall conversion rates and fermentability in a decocted beer. Breaking down proteins in the cellular walls of the grains may also contribute to enhanced clarity in the finished beer.

Clarity is another advantage of the decoction method. As a portion of the mash is decocted and boiled, the proteins in the wort tend to coagulate and fall out. For a triple decoction mash, three different boils may be used giving a portion of the wort three chances to eliminate some of the protein. Reducing the protein remaining can result in much clearer wort and a clearer finished beer.

The only disadvantages of decoction mashing are the added complexity in terms of equipment and time. To perform a decoction you generally need a separate mash vessel with a heat source to bring the decocted portion of the mash to a boil, in addition to the original mash tun, which still needs to be able to maintain its temperature during long decoction steps. 

Aside from the added equipment, decoction can easily add several hours to your brew day depending on how many stages you use. Each decoction must be drawn off, measured, slowly heated to a boil while constantly stirring, and then mixed back into the main mash to complete each step. A complex triple decoction can easily turn into an all-day affair.

Variations in Decoction 

Before you start a decoction mash you need to select a mash schedule. Since decoction is a technique you could apply to any mash step, it could be used with any step mash profile. The traditional approach is a triple decoction, though obviously a single or double decoction involves a lot less work. When counting steps, the first step is typically reached using a simple infusion of hot water, so a triple decoction actually involves four mash steps, with three separate decoctions after the initial mash-in. You might want to start with a single decoction initially as it is much easier than a triple decoction.

The Triple Decoction

The triple decoction is the traditional approach most brewers associate with Bavarian and Bohemian brewing. The first step is done by adding hot water to the grains in a simple infusion step to achieve a lukewarm temperature of about 99 °F (37 °C). The modern term for this step is called an acid or phytase rest, and it is known to slightly lower the mash pH. Typically it is held for only 20 minutes or so (however, in practice, about two-thirds of the mash stays around this temperature much longer as the first decoction is being heated up).

The first decoction is pulled and used to raise the temperature of the mash to around 122 °F (50 °C) for the second step. While heating the decocted portion up to a boil you want to stir it constantly to reduce the chance of it scorching. The modern term for this is called a protein or beta-glucan rest. It was done to help break down proteins and assist developing enzymes to help mash undermodified malts. However, modern malts are all highly modified, and a protein rest using modern malts can actually reduce protein levels enough to harm the final head retention and body of the beer. As a result, modern brewers typically will skip the protein rest for most barley-based beers and only add a protein rest if brewing beer with a large percentage of protein-rich adjuncts like wheat, flaked barley, oats, or rye. The protein rest typically lasts around 20 minutes.

A second decoction is pulled and used to raise the temperature for the main starch conversion step. This step, which could be anywhere in the 148–156 °F (64–69 °C) range, is where long starch sugar chains are broken down into shorter sugar molecules that are fermentable. This is the main mash step you typically perform in a much shorter single step mash, and will last anywhere from 30 to 80 minutes.

A third decoction is pulled to raise the temperature for the mash-out step and is performed at a mash temperature of around 168–180 °F (76–77 °C). This step slows enzyme activity and also decreases the viscosity of the mash and wort, which will aid in lautering. Typically this is a short step, only 5–10 minutes before you go directly into your lautering process.

While the triple decoction is the standard most closely associated with Bavarian and Bohemian beers, there are alternatives that take less time and still achieve most of the character of a triple decoction.

The Double Decoction

A double decoction is identical to the triple decoction, except that it skips the first decoction and first mash stage (the acid/phytase rest). Instead, the first infusion of water is used to initiate the protein rest, and then two decoctions are performed to reach the starch conversion and mash out steps. However, since you are not performing the first decoction (which aids in overall efficiency), many brewers will alter the main starch conversion step to choose a slightly lower mash temperature to compensate. For example, they might perform the starch conversion step at 148 °F (64 °C) instead of 152 °F (67 °C). Done properly, a double decoction will retain most of the character of a triple decoction, while cutting the mash time by at least
a third.

Single Decoction

The single decoction typically eliminates the later decoction “mash- out” step but preserves the protein rest and main starch conversion step. So you would start by infusing hot water to reach your short protein rest step, and then perform a single decoction mash to reach your main starch conversion step. So only one decoction is performed for this two-step mash.

Many modern brewers don’t want to thin the beer with a protein rest, due to the fact that modern malts are all highly modified, and instead will target a higher temperature range for the first step. Often this is just below the typical starch conversion range — around 144 °F (62 °C). Then the decoction is performed to reach a step temperature near 155 °F (68 °C) for the main conversion. This gives you a mash schedule similar to the high/low two-step mash schedule often used with lagers and results in a high attenuation and clean finish on the beer.

Schmitz Process Decoction

The Schmitz process is a homebrew variant of a single decoction that still develops the desired malty character of the decoction without as much effort as a full triple decoction. It is typically done on a stovetop or in another large mash vessel where you have direct heat available.

The Schmitz process can be thought of as a “reverse” decoction. You start by using either an infusion or direct heat to bring the mash temperature up to 150 °F (66 °C), stirring to avoid scorching. Next you let the grains settle to the bottom and instead of pulling the thickest part of the mash off, you actually pull the hot liquid from the top of the mash and collect it in a separate vessel to the side. Now you actually take the thick grain mash and slowly bring it to a boil for 15 minutes, stirring constantly to avoid scorching. Boiling the grain breaks down cell walls and adds color and malty complexity.

Next you need to cool the boiled mash down, stir in the liquid you set aside earlier and continue to mash at around 150 °F (66 °C) until starch conversion is complete.

Let’s Do Some Math

Though we’ve covered the basic decoction process, there are some additional details like how much water to use and how to determine the fraction of mash to pull that are important when performing any of the previously mentioned decoction mash techniques.

While traditional infusion mashes are typically done at a relatively thick ratio of around 1.5 quarts/lb. (3.1 L/kg), it is not uncommon for decoction to use water-to-grain ratios that are as high as 1.9–2.4 qts./lb. (4–5 L/kg). The additional water can reduce the chance of scorching when heating the mash, and was used in many older decoction schedules, but you need to carefully consider what will fit in your mash tun as well as the volume of your separate boiler. Ratios below 2 qts./lb. (4.2 L/kg) are more commonly used and more manageable for brewers.

The first mash step is reached via hot water infusion, just as you would do for a traditional infusion mash. Calculating the water temperature for the infusion step can be done using your brewing software or an online infusion calculator, and you merely heat the water needed to reach the first step temperature and then mix in your grains.

For the decoction steps, you will need to calculate the volume of mash you need to pull and boil. Typically this is expressed as a fraction of the total mash volume. It is best to pull from the thickest part of the mash-grain mixture for each decoction. To get an approximate fraction to pull you can use brewing software or the following equation from Marc de Jong, Homebrew Digest:

Fraction = (TS – T0)/(TB – T0 – X)

For the equation, fraction will be the fraction of the total mash volume we are going to decoct and boil. All temperatures are in degrees Celsius. T0 is the starting temperature of the mash. TS is the temperature of the target step we are moving to next. TB is the boiling temperature, which is 100 °C unless you are working at high altitude. Finally, X is a factor to compensate for your equipment thermal losses. Typically 10–18 °C is a good number. Use X=14 °C as a starting point, but you can adjust this up if your step temperatures come in too high, or down if your step temperatures are too low.

Here is an example of a decoction with the equation above, using 4 °C
(7 °F) for environmental loss.

T0 = 60 °C
TS = 72 °C
TB = 100 °C
X = 4 °C
Fraction = (72-60)/(100-60-4) = 33%

Some Closing Decoction Tips

At this point, I’ve covered everything you need to know to perform your first decoction, but here are a few summary tips to make sure your decoction is a success: 

• Plan ahead and make sure you have allotted extra time in your brew day for performing your decoction and also the additional cleanup needed.

• Ensure that you have the extra equipment needed including a separate vessel and heat source to bring the decocted portion to a boil, along with tools (large ladles or small pots and gloves) to safely move large volumes of hot wort around.

• Choose your decoction schedule in advance. For your first decoction, a single decoction or Schmitz process decoction is usually best.

• Determine your water-to-grain ratio up front when calculating the first infusion step, and make sure you have enough volume for both water and grain in your mash tun.

• Calculate the fraction of the mash you are going to decoct at each step in advance, and have a method for measuring the volumes as you pull the decoctions.

• Pull your decoction fraction from the thickest part of the mash (you can use a ladle for a small system, or a pot with a long handle or something similar for a larger home system). 

• Have a way to maintain the main mash at a steady temperature while you are decocting the separate portion. Often a mash cooler works well for maintaining a steady temperature.

• When bringing your decoction to a boil, stir it continuously to avoid scorching the mash on the bottom of the boil pot.

• Be very careful moving around hot pots and transferring large volumes of boiling hot mash. It is very easy to get burned, so use gloves and ladle the mash back and forth, or perhaps using a small pot rather than trying to dump hot mash directly between vessels.

• You can use small volumes of hot or cold water to adjust the step temperature if you don’t precisely hit your target temperatures.

• When the mash is done, you lauter, boil, chill, and ferment your beer just as with any traditional beer, so don’t make changes outside of the mashing process to your regular routine.


While some brewers do see decoction mashing as a real chore, it can be fun to get a few friends together and make a day of it and try something new. The precise malty but clean finish you get from a decoction mash is nearly impossible to duplicate using other methods. Decoction is a great way to add something special and unique to your beer, and is appropriate for a wide variety of European beer styles. I hope you enjoy your first decoction and the unique beer you’ve made!


1 Pasteur, Louis, Studies in Fermentation, 1879. English translation re-printed 2005 ISBN 0-9662084-2-0 p10. Citing Moniteur de la Brasserie, 23 April 1871.

Issue: October 2019