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, 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 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.
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.
The first step, before adding adjuncts, is to mash-in a small quantity of malted barley in the hot water of the cereal cooker. The alpha-amylase of the malt will hydrolyze the gelatinized starch, rendering the cooker mash fluid enough for pumping. The quantity of malt used depends upon the enzymatic power of the malt, the nature of the adjuncts, and the heating cycle of the cooker. A typical malt charge, according to Dougherty, is usually 10 to 20 percent of the total amount of cereal used (Dougherty, 1977).
About the time the adjuncts are being added to the cereal cooker, the malt and water are added to the mash tun to begin a peptonizing rest within the same range, 38 to 50 degrees C (100–131°F) (Dougherty, 1977). After 15 to 30 minutes of peptonizing, the temperature is raised to 50 degrees C (131°F).
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