Double Dipping: A Double-Decoction Lesson
Mention the word “decoction” to most homebrewers and you can expect a puzzled reflection. Even among the most ardent all-grain brewers, decoction may elicit a bit of skepticism. Decoction mashing has a reputation for being time-consuming, difficult to control and not worth much in comparison to other mashing methods. I hope to convince you that at least two of the three preconceptions are wrong.
There are three basic mashing regimens. Single infusion is the easiest, both conceptually and in practice. This is the method used in English breweries. It involves the “infusion” of the grist (milled malt) with hot water to attain the “saccharification rest” at 148° to 158° F. (Saccharification is the process of breaking starch into simpler sugars.) This mash schedule is appropriate for well-modified malts — which constitute virtually all malts available to homebrewers over the past dozen years. Single infusion is the most common mashing regimen employed by homebrewers, brewpubs and micros for the production of both lagers and ales.
The other two mash schedules, decoction and step-mash, are similar to each other in that the mash includes additional rests at lower temperatures, typically a protein rest at 122° F and perhaps an acid rest at 100° F. The main role of the acid rest is to increase the acidity — lower the pH — of the mash and subsequently the beer. The principle roles of the protein rest are to provide nutrients essential for healthy fermentation, reduce haze and increase foam.
Decoction differs from step-mash in the manner in which the mash temperature is raised. In step-mashing, the mash tun is heated (on a stove or outdoor cooker) to raise the mash from one rest to another. In decoction mashing, a portion of the mash is removed from the mash tun, brought to a boil in another kettle and then added back to the mash tun to “jump” the temperature to the next rest.
Decoction mashing was historically used throughout central Europe, including Germany and the Czech Republic. Decoction brewing is widely used in the Czech Republic to this day. However, many German breweries have moved to step-mashing. This trend away from the traditional decoction mash is likely to continue in Germany, and it is my expectation that many Czech breweries will ultimately move away from decoction as well.
There are two forces driving decoction toward, if not extinction, then rarity. The first is simple economics and the second is malthouse efficiency and technology.
In the simplest terms, malting and mashing are both processes along the continuum in the conversion of the food reserves of the barleycorn into sugars. (In fact, the Czech word for brewer and maltster is the same, “sladek.”) The maltster first changes the hard barleycorns with insoluble starches into soft malt with soluble starches. The brewer then breaks the starches down to sugars in the mash. But there’s a region in which malting and mashing overlap. The malting process may be stopped at a point that requires the brewer to employ an acid and protein rest in the mash — such malt is said to be “under-modified.” Or the malting process may be extended to a point that renders these rests unnecessary — this malt is “well-modified.”
The cost of conducting acid and protein rests in the brewery is considerable, while the additional cost to the maltster of producing well-modified malt is negligible. That explains the economic motivation towards single infusion and away from decoction. Step-mashing is also less time-consuming and uses less energy than decoction.
This begs the question, why did anyone ever use a decoction mash? Prior to the last part of the 20th century, malting was a poorly controlled process by today’s standards. The greatest difficulty in malting is getting all the barleycorns to march in lockstep toward modification. Imagine a field of corn in which all the plants spring from the earth at the same moment! That is essentially the task of the maltster. The reality is that there is a distribution of modification within each batch of malt — some under-modified, some well-modified and everything in between. This distribution is usually very small today, due to the technology employed in malthouses and the systematic control of farming practices and seed selection. However, modification distribution was quite varied prior to this century. And decoction is preferable when malt has different levels of modification.
Daniel Fahrenheit invented the mercury thermometer in the early 18th century. Beer, thank goodness, was invented much earlier. So the decoction mash predates the thermometer. A decoction mash does not actually require the use of a thermometer, since the temperature of each rest is determined solely by mixing a known volume of boiling mash with a known volume of the remaining mash.
Although decoction is the traditional mashing method of continental Europe, this is not the case for the British Isles, where single infusion has its roots. The reasons for this appear to be a complex interplay of agricultural conditions, barley varieties and beer styles. Historically, England has favored the production of ales, while in other parts of Europe, lagers have long been favored. Because pale ales are darker golden in color than pilsners, the pale-alt malt needed to be kilned longer than the malt used to make lagers.
Furthermore, the weather in Great Britain is wet and warm, without harsh winters, while northern continental Europe has harsh winters followed by relatively dry and occasional hot summers. This led to English barley varieties that were lower in protein and plumper than those of Europe, which in turn led to both easier modification of English barleys, as well as production of clear beer without the rigorous decoction mash. Much of this may be a chicken-and-egg question; did desire for ale lead to these barleys or did the growing conditions lead to barleys suitable for ale?
This underscores one of the reasons that under-modified malt has become increasingly scarce, even in continental Europe. The market demand for well-modified malt has resulted in the development of hybrids best suited to a high degree of modification, while varieties suitable for under-modified malt have been phased out.
I had the pleasure of traveling extensively in the Czech Republic over the past two years, visiting numerous breweries and maltings. I spent an entire day, 14 hours, quizzing a Czech brewmaster as a dark lager moved from doughing-in to pitching yeast. The decoction procedure detailed here reflects that experience. But the procedure is tailored to common homebrewing equipment and includes several tips that make the process easier and less time-consuming.
The Kettles
Decoction requires 3 kettles, or 2 kettles and a plastic pail or cooler. The kettles should be 7-gallon capacity or larger if you are making 5-gallon batches. Both kettles need drains, and one must also have a false bottom.
The third kettle, or the plastic pail, will be used for pure water — first for cool water, which we will use to adjust rest temperatures, and later to hold hot sparge water. Two kettles are needed for the mash. One of these doubles as a boiling kettle. You will also need the usual mash equipment of thermometer and spoon or paddle.
The Malt
Scores of homebrewing articles and books cite this mantra: “Use single infusion with well-modified malts and step-mash or decoction with under-modified malts.” Although this counsel certainly has merit, homebrewers have had little opportunity to use under-modified malt due to its scarcity. The result is that homebrewers have been forced to use well-modified or moderately-modified malts in decoction and step-mashes. This has led to much debate over the past decade regarding the merits of decoction, as well as step-mashing, with modern well-modified malts.
On one hand, many brewers believe acid and protein rests and decoctions impart desirable and authentic flavors, as well as improve foam. This was the prevailing view in most homebrewing books and articles until recently. However, scientific literature has documented the negative effects of using malts intended for single infusion mashing in decoction or step-mashing. In particular, a protein rest at 122° F may actually result in poor foam! This, ironically, is quite the opposite of one of the supposed benefits of a protein rest. This is the reason that Anheuser-Busch skips the protein rest and many German breweries use a mash schedule called “hochkurz maischverfahren” (high-short mashing scheme), a simplified decoction mash that begins at a high temperature, 140° F, thus skipping the protein rest.
There are numerous other defects — or at least differences — in decoction beers brewed with well-modified malts. Higher pH, sulfur dioxide levels, and the levels and types of esters and higher alcohols all reflect on the perceived quality of the beer.
Homebrewers have used virtually every type of malt for decoction mashing. Regardless of the opposing views regarding protein rests (my own view is that the negative effects are minimal if the rest is brief), beers made from a decoction mash are certainly different from those made from step-mash or single infusion. The decoctions deepen the color and flavor of the beer. The pH of decoction beers is slightly lower, as well. One of the well-documented trends in German beers over the past two decades is the increase in beer pH, which is perceived as a decrease in the “liveliness” of the beer. This defect is directly attributable to modern well-modified malts.
The only under-modified malt available in North America is Budvar malt. Budweiser Budvar, the “original Budweiser,” is a Bohemian brewery that insists on malt made from the Forum variety, grown in the Hana region of Moravia. The brewery specifies malt that is under-modified to match the decoction mash employed at the brewery for over a century.
The English pale malts (Beeston, Muntons, Pauls, Hugh-Baird, Crisp) as well as the American pale malts (Briess, Great Western, Schreier) and the Belgian DeWolf-Cosyns malts are all well-modified. The modification differences between lager (a.k.a. pilsner) malts and pale ale malts from these maltings are generally quite small. Some German malts, such as those from Weyermann, Weisheimer and Durst, are moderately-modified.
The Water
Czech lagers are brewed with very soft water. The water of northern Germany is less soft, but great pilsners are brewed there as well. If your water source is hard and alkaline, I would suggest diluting by half or perhaps two-thirds with RO or distilled water. If you are not sure about the calcium content, add a pinch of calcium chloride.
Double Decoction
Many German breweries employ single decoction, while most Czech breweries use double decoction. Triple decoction is reportedly employed at Pilsner Urquell. Single, double, and triple simply refer to the number of portions of the mash that are removed and boiled. Both triple and double decoction typically involve the same four temperature rests. For clarity, I will give details for a double-decoction mash of five gallons of pilsner beer.
Step 1: Dough-In and Acid Rest
Doughing-in, also calling mashing-in, is mixing the strike water with the crushed malt. To do it, bring 17 quarts (4.25 gallons) of water to 101° F. Mix in 8.5 lbs of milled malt. Add a couple of pounds at a time, then stir with a spoon to thoroughly mix. The temperature should be 98° F, but don’t worry if it’s anywhere between 96° and 100° F. Let this sit for 10 to 15 minutes.
The decoction mash for Pilsner is a very thin mash, with roughly 2 to 2.5 quarts of water per pound of malt. This is at least 50 percent more water than for a single-infusion mash.
Here’s an equation for determining the temperature of the strike water. This equation applies to
single-infusion mashes as well:
Tw = TD[2.08 x M + 0.4] – [0.4 x Tg]
2.08 x M
Where TD is the dough-in temperature in °F, Tg is the temperature of the grist in °F, M is the water/grist ratio in quarts/pound, and Tw is the strike water temperature in °F.
Tip 1. Use 2 quarts of water per pound of grain for doughing-in. This allows you to add more water later in the mash to adjust the temperature. Applying the above equation, the strike water need only be at 101° F if you’re using 2 quarts/lb. for a 98° F dough-in (assuming the grain is 70° F). Note that 1 pound of malt in 2 quarts of water results in 2.5 quarts of mash. For this mash (17 quarts of water and 8.5 lbs. of grist), the total mash volume will be 21 quarts (5.25 gallons).
Step 2: Protein Rest
Turn burner on and raise the mash temperature — at a rate of 2° F per minute — until it is between 122° and 127° F. Hold at this temperature for 15 minutes.
At this point, you are conducting a step-mash. It is important that you apply sufficient heat to move quickly to the protein rest stage. Stir the mash occasionally to even out the heat and prevent scorching.
Step 3: First Decoction
Use a small pot to ladle 10.5 quarts (almost 2.65 gallons) of the mash into another kettle. Take the thin mash at the top, leaving the thick mash at the bottom.
Apply heat to the thick mash that you left behind in the original pot to bring the temperature to 145° to 149° F (again, at 2° F per minute). Rest for 10 to 15 minutes.
Then raise the temperature to 163° to 165° F for a 10 to 15 minute rest.
Now bring this to a boil for 20 minutes. Stir the mash occasionally, particularly as it reaches a boil. Note: The thin part of the mash, which you moved to another kettle, should be kept between 122° and 127° F during this entire step.
The greatest difficulty in decoction brewing is pulling the proper amount off the mash, which when boiled and added back, will raise the entire mash temperature the precise amount.
Tip 2. The volume of the first decoction will depend on your system, but I would suggest taking 45 to 50 percent of the total mash. This will likely result in overshooting the temperature. Keep some cold water handy, and if you overshoot, bring the temperature down with the water (see Tip One). The following equation (adapted from “Technology Brewing and Malting” by Wolfgang Kunze) provides an estimate of the amount of your decoction:
Decoction Volume in quarts = (temperature increase in °C ) x (Total Mash Volume in quarts)/(90 °C – temperature of unboiled mash in °C).
The decoction is the thick portion of the mash, which is at the bottom. In a single-infusion mash, the entire mash is said to “float” like porridge. However, in a thin decoction mash, the grain sinks to the bottom while the thin watery portion remains at the top.
Tip 3. How do you get the thick portion off the bottom of the kettle if you cannot pump it from the bottom as is done in commercial breweries? Quite simply, you don’t. Remove the thin portion from the top (you will also need to remove some of the thick mash to achieve the 50 percent left for the decoction). I use a small pot to ladle the mash over. In other words, the decoction is what is left behind.
It is important to note that the enzymes essential for the saccharification step are principally in the thin liquid portion of the mash. If one were to boil this portion, the enzymes would be denatured and rendered useless. This explains the wise counsel to never boil all the mash or even the thin portion. However, I have witnessed one Czech brewery that uses the thin portion for the first decoction, but not the second. So don’t fret about how much of the thin portion you boil, as long as you exercise reasonable care.
Step 4: Add Decoction Back
Turn off heat and add the thick decoction mash, which is boiling, into the kettle that has the thin portion of the mash. (Remember that the thin portion of the mash has been sitting at 122° to 127° F during this time.) The entire mash should now be at 145° to 149° F. If it is too high, add some water. Rest 10 to 15 minutes. Be careful when handling the boiling liquid. I recommend using the small pot to ladle at least some of the boiling mash over.
Step 5: Second Decoction
Use a small pot to ladle 8.5 quarts (a little over 2 gallons) of the mash into another kettle. Take the thin mash at the top, leaving the thick mash at the bottom.
Apply heat to the thick mash that you left behind to bring the temperature to 163° to 165° F (at 2° F per minute) and rest for 10 to 15 minutes. Now bring this to a boil for 20 minutes. Stir the mash occasionally to prevent scorching.
The second decoction will be larger than the first, on the order of 50 to 60 percent of the mash. I recommend using the upper range of 55 to 60 percent. So ladle the thin top portion and some of the thick mash to another kettle.
Step 6: Add Decoction Back
Turn off heat and add the thick decoction mash, which is boiling, into the kettle that has the thin portion of the mash. This thin portion has been sitting at 145° to 149° F.
This should bring the entire mash to 171° to 172° F. If it is too high, add some cold water to bring it within range. Rest for 30 minutes.
Step 7: Siphon off the Top
Now you’re ready to lauter, the process of collecting the extract from the mash tun. You will find the thin portion of the mash to be extremely clear — much of the break material, typically found in the boiling kettle, is in the mash tun due to the boiling of the decoctions.
Siphon the top, clear portion from the mash into the boiling kettle. Do not siphon the cloudy wort. To start the siphon, fill plastic tubing with water and quickly immerse one end into the mash and the other into the kettle.
Tip 5. The top portion is so clear that you need not lauter it. The first wort can actually come off the top through a siphon hose. This will be as much as 40 percent of the total mash volume (about 2 gallons in this recipe). It is common in Czech breweries to remove the first runnings in this manner. This is a great time-saving technique.
Step 8: Lauter and Sparge
Heat 3 gallons of plain water to 176° F. This water will be used for sparging — rinsing the extract from the mash. Now begin lautering by opening the valve on your mash tun. Collect the first runnings, which will be cloudy, in a small pot until the runnings become clear. Pour the runnings back into the mash tun. Recirculate the runoff until it becomes clear; this should only take a minute for a decoction mash.
Note that the rate of the run-off depends on the surface area of the grain bed. In a typical homebrew set-up, this equates to about 1 pint per minute.
Carefully monitor the depth of the liquid above the grain bed. When it reaches a depth of less than 1 to 2 inches, add sparge water at the same rate that you are collecting the runoff. Continue to collect the runoff until you reach a boiling kettle volume of 5.5 gallons
You will not need to add any sparge water for some time because of the thin mash. Note: If the wort drops below the level of the grain bed, and then you add sparge water, you run the risk of getting a stuck mash.
Tip 6. Expect a decoction mash to get stuck. In fact, it’s unusual for the mash not to get stuck. There are two reasons for this. First, you have precipitated a lot of break material during the decoction boils. Also, boiled husks do not make a good filter medium.
Here’s a little trick that I have used with great success. Add a pound of rice hulls to the mash during the last rest. The rice hulls improve the filter medium and thus ease the lauter.
If the runoff gets stuck, stop the lautering process, add some 176° F sparge water and stir gently. Then lauter again, remembering to recirculate for a minute until the runoff clears. You may have to repeat this two or three times if you do not use rice hulls during the last rest.
Step 9: Boil and Ferment
Now you are ready to move on to the usual boil and fermentation stages. Traditional Central European breweries employ a 1.5- or even 2-hour boil. In the interest of time, I never exceed 1.5 hours. A good rolling boil with about 10 percent evaporation is fine.
German and Czech brewers historically have used 3 hop additions in equal amounts: the first addition for 1.5 hours, the second for 1 hour, and the final for 20 to 30 minutes. Budweiser Budvar uses a method called “first-wort hopping,” in which hops are added to the first runnings during lautering (for more on first-wort hopping, see page 45). The second addition is at the beginning of the boil; the final addition is 30 minutes before the end of the boil.
Decoction Differences for Dark and Strong Beers
The decoction procedure I have detailed is appropriate for pilsners or other pale lagers. There are a couple of differences when brewing dark beers. The rests for pilsners are each 10 to 15 minutes, except the last, which is 30 minutes. When brewing a dark lager, the rests are typically 5 to 10 minutes longer. Additionally, black malt is never boiled; it is added during the last rest only. Furthermore, dark or strong beers such as bock and Oktoberfests are typically made from thicker mashes than are pilsners. For example, a water/grist ratio of 1.5 quarts/pound would be appropriate for a bock.
Lynne O’Connor (nee Karas), a second-generation Texas Czech, owns St. Patrick’s of Texas Brewers Supply in Austin. She is greatly indebted to the following Czech brewers and maltsters: Petr D., Rosta R., Jiri R., Josef V., Vlastimil Z., and two anonymous Czechs. Their knowledge is exceeded only by their patience.
Four Beers, Double Decoction
Hoppy Czech Pils
(5 gallons, all-grain)
OG = 1.051 FG = 1.010 IBUs = 45
Ingredients
8.5 lbs. under-modified or moderately-modified malt
Three 1 oz. additions of Czech Saaz hops (at 90 minutes, 60 minutes, 20 minutes)
Czech Pils yeast (Wyeast 2278)
1 cup corn sugar for priming
Step by Step
Follow double-decoction procedure outlined in the article. Primary fermentation at 48° F for 12 days. Lager at 32 to 36° F for 3 to 9 weeks.
Original Budweiser
(5 gallons, all-grain)
OG = 1.051 FG = 1.010 IBUs = 22
Ingredients
9.75 lbs. under-modified or moderately-modified malt
Three 0.75 oz. additions of Czech Saaz whole leaf hops (at first runnings, 60 minutes and 30 minutes)
Budweiser Budvar (Wyeast 2000)
1 cup corn sugar for priming
Step by Step
Follow double-decoction procedure. If using pellet hops, slightly reduce the amount of hops. Primary fermentation at 48° F for 12 days. Lager at 32° to 36° F for 3 to 9 weeks.
Note: This recipe uses more grain than the previous pilsner recipe, although they have the same starting gravity. Budweiser Budvar does not sparge the spent grains to the extent employed at most breweries. This results in decreased efficiency (only 27 to 28 points per pound) but produces a beer that is smoother, with a rounder flavor.
German Bock
(5 gallons, all-grain)
OG= 1.068 FG = 1.016 IBUs = 25
Ingredients
6 lbs. under-modified or moderately-modified malt
5 lbs. light Munich malt (10° Lovibond)
1/2 lb. crystal malt (50° to 60° Lovibond)
1/3 lb. black patent malt
Three 1 oz. additions of Hallertau Mittelfrueh hops (at 90 min., 60 min. and 30 min.)
Bavarian Yeast (Wyeast 2206)
1 cup corn sugar for priming
Step by Step
Follow double-decoction procedure, with the exception of using a thicker mash. Do not add the black patent malt until the last rest. Primary fermentation at 48° F for 16 days. Lager at 32° to 36° F for 5 to 12 weeks.
German Märzen
(5 gallons, all-grain)
OG = 1.058 FG = 1.012 IBUs = 26
Ingredients
8.5 lbs. under-modified or moderately-modified malt
3.25 lbs. light Munich malt (<10° Lovibond)
8 oz. DeWolf-Cosyns aromatic malt or Weyermann melanoidin malt
1 oz. addition of Hallertau Mittelfrueh hops (at 90 min.)
0.5 oz. additions of Tettnang (at 60 min. and 30 min.)
Bohemian yeast (Wyeast 2124)
1 cup corn sugar for priming
Step by Step
Follow double-decoction procedure, with a thicker mash. Primary fermentation at 48° F for 15 days. Lager at 32° to 36° F for 5 to 12 weeks.
