Decoction Mashing, Part 1

Decoction Mashing, Part 1

Demystification of the Decoction Mash

(This post was restored from the old site, and contains some really good and knowledgeable information, and deserves to be kept up. If you are reading this David and would like it removed just contact us) Props to David for the awesome write-up.
By David Cordrey

Of the three mashing methods Single Infusion, Step Infusion and Decoction, decoction mashing remains a mystery to many homebrewers. Single infusion mashing is by far the most common mashing technique and is employed by most all-grain homebrewers. Some homebrewers use a step infusion or temperature controlled mash which includes a protein rest, but few and far between are homebrewers that have ever tried to conduct a decoction mash.

In this article, I’ll attempt to demystify the decoction mash by explaining what decoction mashing is, what it’s benefits are and what beer styles have traditionally used decoction mashing. In Part 2, I’ll talk about how to successfully conduct a decoction mash in the homebrewery.

Webster’s defines:

  • “Decoct” 1) to extract the flavor of by boiling 2) boil down, concentrate
  • “Decoction” 1) the act or process of decocting 2) the extract obtained by decocting

From these definitions it stands to reason that a decoction mash involves the boiling of the water/malt mixture, and that the intent is to extract and/or concentrate flavors.

But how can that be? The first thing an all grain brewer learns is that if a mash is boiled, the precious amylase enzymes will be destroyed preventing starch conversion, and excessive amounts of tannins will be leached from the grain husks, leaving an undesirable astringent flavor. The answer to this paradox, as you’ll soon see, is that careful technique overcomes these potential problems; indeed, a decoction mash when performed properly results in a beer with the highest malt flavor profile and highest extract yield of the three mashing techniques. Decoction mashing also results in less hot and cold break material, and reduces the mash pH naturally, without the addition of dark malts, lactic acid or other water treatments.

In decoction mashing, a portion of the mash is removed from the mash tun and is transferred to a boiling pot. This portion is called the decoction, and it is heated slowly to bring it to a boil. After boiling for a period of time the decoction is added back to the main mash, thereby raising it’s temperature. In this respect, the decoction mash is similar to the step mash or temperature controlled mash. For example, the initial mash temperature and volume of the decoction can be chosen so that the temperature rise goes from the protein rest temperature to the sacharification rest (starch conversion) temperature. This would be called a single decoction mash because only one decoction was made. An additional decoction can be made to raise the mash temperature again to mash out (double decoction) or a total three decoctions (triple decoction) could be used to achieve an acid rest – protein rest – sacharification rest – mash out profile.

Long ago brewers had worked out the details of decoction mashing for beer making – even before the thermometer had been adopted by brewers. Proper strike water temperature was by achieved mixing measured volumes of boiling and ambient temperature water, and mash rest temperatures were achieved by mixing boiling and non boiling mash fractions. Through trial and error, good luck and patience these early brewers discovered the proportions of each needed to effectively step through the various temperatures to acidify the mash, degrade proteins, and convert the malts starch into the fermentable malt sugars.

In fact, a simple infusion mash using the under modified malts of this period would have produced weak, hazy, inferior beer. Decoction mashing was an enabling technology for clear pale beers like those produced in Pilzn. You see, by boiling the grain, starches dissolve and insoluble proteins are denatured and coagulate as a scum on the top. The vital amylase enzymes are quite soluble, so if a “thick” decoction mash is pulled for boiling, the “thin” rest mash contains almost all of the enzymes where they are safe from heat degradation. When the decoction is added back, the dissolved starches are immediately available for the enzymes in the rest mash to go to work on, and the rest mash temperature is raised. The proteins that coagulate in the decoction are usually skimmed off the top before the decoction is added back to the rest mash, which improves wort clarity.

Eventually, maltsters in Britain learned how to make higher modified malt, the thermometer was accepted as a brewing tool and infusion mashing was born. This technique enabled shorter brewing sessions, the use of less fuel and in general lowered the cost of beer; all good things considering beer sustained many a laborer during Britain’s industrial revolution.

Decoction mashing did not die. In fact, to this day most European lagers still use a decoction mash, even though their malts are now have a high degree of modification. And not just because they are steeped in tradition. Infusion mashing is not prohibited by the Reinheitsgebot. But, decoction mashing produces a richer malt profile with complex caramelized flavors that are the hallmarks of most continental European beer styles, particularly Pilsner, Marzen, Bock, and especially Dopplebock.

The specific flavoring agents produced by decoction mashing have not been rigorously identified by chemical name, but it is presumed that they are the result of certain browning (melanoidin) reactions and caramelization. These are the same types of reactions that happen when you cook a roast in the oven. An analogy can be drawn between oven roasting vs. microwaving a roast and decoction vs. infusion mashing malt. The browning reactions require the presence of protein and sugars and carmelization requires a high sugar concentration. While carmelization does occur in the main boil, the concentration of sugars is generally higher in the mash so decoction mashing will give more carmelization than wort boiling. The browning reactions are not as prevelant in the boil because the wort has been separated from the grist, and there is not a sufficient amount of protein in clear wort to support them as much. These browning reactions, and high sugar content in the decoction also serve to lower the pH of the decoction so that leaching of tannins form the grains husk is not a problem.

There has been a trend in continental Europe recently of brewers moving away from the triple and double decoctions as a matter of economics. Many are now using a single decoction, though rumors have it that a few are either using or experimenting with infusion mashes. Today’s highly modified malts, the availability of large variety of specialty malts, superior milling, automated temperature control and superior water chemistry have all lessened the requirement for triple decoction mashes. However, even a single decoction will produce malt flavors unobtainable by any other means.

Hopefully the craft of decoction mashing won’t be entirely lost among commercial brewers for economic reasons. As homebrewers we should be prepared to carry the torch and keep this historic and beneficial technique alive. In Part 2, I’ll explain how to get started decoction mashing at home with a minimum investment.

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