As brewing has evolved some techniques that were once considered essential have become obsolete. Decoction mashing, however, arguably maintains  important aspects of crafting a well-respected beer. But its role has changed. In earlier days it was a necessary step in breaking down undermodified malts, which are less prevalent now. Today die-hard decoction mashers are convinced of decoction’s finer attributes: that it makes a richer, more complex beer and adds a sense of tradition.     

Before the development of modern malting techniques, two basic types of malt were produced. The difference between the two is based on modification, the degree of enzymatic degradation within the malt kernel. These two types of malt, the well modified and the undermodified, largely influenced the mashing procedure of the brewers who used them.

The well-modified malt of the British was perfectly suited for a single-temperature infusion mash. Because most of the degradation occurred during malting, British malt released its extract very easily. The same cannot be said for the undermodified malts of continental Europe, specifically Germany. These malts were less modified. The hard tips of the malt were evidence of undegraded barley.

In an almost Darwinian responsiveness, continental brewers developed a mashing method that compensated for their partially malted barley. Known as decoction mashing, this method compensates for a lack of enzymatic decomposition by removing one-third of the mash, boiling it, and returning it to the main mash to increase the main-mash temperature. This heat-intensive process breaks down chemical structures in the malt, making them available to enzymes in the mash.

Traditionally, the mash regimen called a triple decoction required three decoctions and four temperature rests: an acid rest at 95° F, a protein rest at 121° to 131° F, a starch conversion at 150° to 158° F, and a mash-out rest at 165° to 168° F. Today the less time-
consuming double- and single-decoction methods are more common.

The double decoction usually starts with a temperature of 128° to 131° F that is increased to 152° to 155° F and finally 165° to 168° F by two decoctions. The single decoction requires only one decoction to raise the mash temperature either from the starting point, 128° to 131° F, to a mash-out at 152° to 155° F or from 152° to 155° F to mash-out at 165° to 168° F.

Modern malting techniques have made undermodified malt such as that formerly found in Germany very rare. Likewise, the process of decoction mashing is slowly becoming somewhat of a novelty in the brewing industry. No longer a necessity to convert modern malts, the process is also time consuming and expensive in terms of energy consumption. Still, some die-hard decoction brewers persist, claiming that the process yields more extract per pound of malt than other methods and creates a richer, more complex beer due to the flavorful melanoidins (dark organic compounds) produced by boiling the grains. For German brewers decoction mashing reflects a part of their brewing history. Continuing to carry the torch of decoction mashing in an age of streamlined, high-tech brewing adds a sense of tradition and uniqueness to their products.

Homebrewing by decoction mash is an intriguing and challenging reenactment of a brewing tradition. The decoction mashing process, although appropriate for all German styles, best brings out the maltiness of dark German beers such as bock, Märzen, and dunkel. The following procedure details the process of a double decoction mash.

The protein rest. Mash the grains with the mash water to reach a temperature of 128° F (2.2 pounds of malt into 3 liters of 140° F water, for example). Mix thoroughly so that no clumps of crushed grain remain. During this step, called the protein rest, some protein as well as gummy beta-glucans may be degraded.

The first decoction. After the grains have been properly mixed (all clumps are gone and the temperature has stabilized), remove 30 to 40 percent of the mash by volume. This may be difficult to ascertain on the spot. By calibrating your mash tun with notches for every gallon, a more precise amount of mash can be removed. It is important to remove the thickest portion of the mash. Most of the enzymes are in the liquid portion and should remain with the main mash. A slotted spoon may help accomplish this. The decoction should then be placed in a pot and heated slowly to 158° F, where it is held for a 15-minute starch conversion rest. After the rest, slowly bring the decoction to a boil while stirring continuously to avoid scorching. Boil for 15 minutes. If the decoction becomes too dry, it will easily burn. Adding water and stirring will prevent this.

The starch conversion rest. By mixing the boiling decoction into the main mash, the total mash temperature is increased to a conversion temperature between 152° and 155° F. When adding back the decoction, mix the boiling grains into the main mash in increments. Be sure not to overshoot the desired temperature. Allow the main mash to rest undisturbed for 30 minutes before removing the next decoction.

The second decoction. Repeat the decoction procedure. The goal here is to raise the main mash temperature to mash-out temperature, 165° to 168° F. The wort recirculation, run-off, and sparge can then begin.

Five Decoction Tips  

• Always stir the decoction to avoid scorching.
• Use an insulated mash tun to maintain rest temperatures in the main mash.
• Mix decoctions incrementally into the main mash to avoid overshooting target temperatures.
• Remove the thickest part of the mash for decoction, but allow enough moisture to avoid scorching. Add water if needed.
• Pay attention to time and temperatures and take good notes.