Carry Brewtech · Difference between Infusion Mashing and Decoction for Brewing Beer

Decoction mashing is a traditional and intensive method of mashing. While the method was once used by most breweries, today decoction is a controversial topic among brewers. Many German brewers (among others) claim that it develops malt character, depth, and superior foam. Others feel that it is a waste of energy and time, and is unnecessary now that modern well-modified malts are available to everyone.

The basic principle of decoction is to remove a part of the mash, boil it, and return it to the main mash, which is held at a constant temperature.

Historically, mashing systems have evolved largely as a result of the advantages or for that matter the disadvantages inherent in the available brewing ingredients: water, malt, and adjuncts. Mashing systems vary widely but are conveniently grouped under three methods: infusion mashing, decoction mashing, and double mashing. Infusion mashing is a mashing technique where hot liquor (i.e., brewing water) is blended with malts to create a mash that undergoes one rest (e.g., saccharification temperature) or a series of rests at different temperatures. Infusion mashing differs from the other mashing systems in that it takes place in one vessel, the mash tun or mash/lauter tun, which is used for both starch conversion and wort separation. Decoction mashing involves boiling a portion of the mash in a mash kettle at various temperature rests and then returning them to the mash mixer (also known as the mash conversion vessel), raising the temperature.

Infusion Mashing

Infusion mashing, although not as popular, is a classical British method of brewing ales and stouts, where the brewer produces and recovers the extract at a single mash temperature, called the conversion temperature. Unlike other mashing methods, traditional infusion mashing doesn’t require a series of different temperatures and rests. The conversion temperature represents a compromise between the optimal temperatures for alpha- and beta-amylase. Any deviations from the intended temperature could affect the beer since there is only one temperature determining makeup.

Single Mash Infusion

Grains that have been “well-modified” (i.e., malted to maximize their conversion potential) usually just require a one-step mash, which is called a single infusion mash. A single infusion mash only involves one rest, at saccharification temperature at which the beta- and alpha-amylase enzymes are active in converting the malt starches into wort sugars.

Temperature-Programmed (“Step”) Mash

The infusion mash was designed to process well modified British ale malts. Due to extensive modification during malting, most of the barley endosperm protein and non-starchy polysaccharide matrix is sufficiently degraded for the brewer to primarily concern themselves with starch extraction and enzymatic conversion. However, as previously discussed, malt quality differs around the world. In practice, this means that the brewer must use more involved mashing sequences (mash profiles) to accomplish the required extract yield, i.e., step mash.

Other Sep-Infusion Programs

Another step-infusion program starts with mashing-in at 35 degrees C (95°F) and holding for 30 minutes before raising the temperature to 40 to 45 degrees C (104–113°F) for a protein rest. The temperature is then either raised slowly to 55 to 65 degrees C (131–149°F), followed by a rise in temperature to 70 degrees C (158°F) for starch conversion, or raised quickly to a temperature of 70 degrees C (158°F) in one step.

Decoction Mashing

Decoction mashing is the traditional method used in the production of wort for bottom-fermentation beers and is most commonly associated with the production of lagers in Germany. It was developed largely as a result of the use of under-modified or enzymatically weak malts. Decoction mashing involves one-, two-, or three-decoction steps, which are referred to as single- double or triple-decoction mashes. The choice of the number of decoctions and the duration of the boil provides control over protein coagulation and malt sugar composition. Unlike infusion mashing, decoction mashing requires two separate vessels: (1) a mash kettle for heating the decoction (often referred to as the mash cooker) and (2) a mash mixer (often referred to as the mash conversion vessel) which is used for mixing the main mash.

Three-Step Mash Decoction System

The three-step decoction involves acid, protein, and saccharification rests. The overall processing time is about 6 hours from mashing-in to lautering. There are many minor variations on the classical triple-decoction mash, especially with regard to the time in heating the decoction, the rate at which the decoction part of the mash is mixed with the main mash, and the length of the stands. Figure 8.4 shows the temperature profile for a three-step-decoction mash.

Two-Step Mash Decoction System

The two-step decoction involves only protein and saccharification rests. The entire process usually takes 2 to 3 hours. As with the three-step decoctions system, there are many minor variations of the two-mash system, especially with regard to speeds of heating, the rate at which the decoction part of the mash is mixed with the main mash, and the lengths of the stands.

Single-Step Decoction System

The single-step decoction involves only a saccharification rest. The entire process usually takes fewer than 2 hours. As with the other decoction systems, there are many minor variations of the single-step mash system.

Double Mashing

The double-mash infusion system is the most widely used system in North America. Double mashing was developed to utilize adjuncts as a source of cheaper extract and as a means of producing lighter, less-satiating beers that have traditionally found favor with North American consumers. Rice and corn are mostly used as adjuncts, though barley, wheat, and sorghum are used to a limited extent. It is important to note that the unmalted grains used in this process do not have active enzymes to convert the starches into sugars.