Enzymatic Reactions Malting and Mashing

The first part of beer manufacture, the enzymatic steps, actually begins far from the brewing facility, in the malting houses that convert barley into malt. It is the malt that serves as the source of the amylases, proteinases, and other enzymes necessary for hydrolysis of large macromolecules, such as starch and protein. For most beers, the malt also serves as the substrates for those enzymes (i.e., malt contains the starch and protein hydrolyzed by malt enzymes). In addition, malt is the primary determinant of color and body characteristics in beer, and influences flavor development. Considering the critical functions that malt contributes to the beer-making process, it is evident that malt quality has a profound influence on beer quality.

The goal of the maltster is to convert barley to malt such that enzyme synthesis is maximized and enzyme activity is stable and well-preserved.The process starts with selection of barley. Several different barley cultivars are used to produce malt. In North America, six-row barley is generally preferred, whereas in Europe and the U.K., two-row barley is used (however, some six-row is also used in Europe and the U.K. and some two-row is used in the United States). Six-row barley contains more protein and less starch than two-row barley. The former also contains a higher level of starch-degrading enzymes, making it more suitable for beers containing adjuncts (discussed below). The harvested barley is then cleaned, graded, and sized. Unless the barley is to be used right away (which is usually not the case), it is dried from about 25% moisture to 10% to 12% so that it can be safely stored.

Malting

Mashing

Fermentation Post-Fermentation

Malting

Mashing

Figure 9-3. Manufacture of beer. The beer manufacture process consists of four distinct stages: malting, in which barley is converted to malt; mashing, in which enzyme and substrate extraction and reactions occur and a suitable growth medium is prepared; fermentation, in which wort sugars are fermented to beer; and post-fermentation, in which the beer is made suitable for consumption.

In the next step, the barley is allowed to germinate or to develop the beginning of a root system. Barley is essentially a seed—if it is held under warm, moist conditions, it will begin to sprout or root, just as it would if it were growing in nature. For malting purposes, germination is done by steeping the barley in cool water at 10°C to 20°C for two to three days, or long enough to increase the moisture from 10% to 12% to about 45%.The steep water is usually changed every twelve hours, in large part to minimize the impact of potential spoilage organisms. During this step, the material is well aerated to promote the germination process. The moist barley is then removed from the steep water and incubated in trays or drums under cool, humid, and well-aerated conditions for two to eight days. The barley initially swells, then germinates, such that

"rootlets" or sprouts appear. Germination is accompanied by the synthesis of myriad enzymes that the barley grain theoretically needs for subsequent growth into new barley plants. The barley has reached its maximum enzyme activity when the sprout reaches a length of one-third the size of the grain.

Next, it is necessary to arrest further germination and to stabilize and preserve the enzymatic activity. This is done by a step-wise drying process, in which the germinated "green" barley is dried incrementally within a temperature range of 45°C to 60°C.The purpose of this slow drying process is to remove water without inactivating enzymes.The dried malt,there-fore, becomes a stable source of enzymes. Since moist heat is more detrimental to enzymes than dry heat, it is important to dry slowly at the start (when the grains are still

Box 9-2. Beer Terminology 101

The manufacture of beer, like that for wine making, bread making, and other food processing technologies, has evolved its own peculiar vocabulary to describe many of the manufacturing steps.Thus, the brewing jargon contains words and phrases unique to beer making, but not so familiar to the casual reader. Given that the origins of modern beer manufacture arose in Germany, it should not be surprising that many of the terms are derived from German. In fact, much of the overall beer vocabulary used by brewers even today contain German expressions. Below are some of the more common terms used in brewing.

Coppers—Vessels used for wort-boiling, called coppers because of the construction material used in their manufacture; even though these kettles are now made from stainless steel, they are still referred to as coppers. Diastase, diastatic power—Refers to the overall starch hydrolyzing activity present in the malt.

Fass—The process of pumping beer into kegs. Kiln—The oven used for drying and cooking malt.

Krausen—The carbon dioxide layer that forms at the top of the fermentation tank; "high krausen" refers to the period at which the krausen reaches its maximum. Krausening—The addition of krausen (containing very active, log phase cells) to beer to promote a secondary fermentation. Lagering—The act of storing or conditioning the beer at low temperature to promote maturation.

Lauter tun—A tank, containing a false bottom, used to promote clarification and separation of the spent grains from the wort. Mash—The heated malt-water mixture, consisting of malt-derived enzymes and substrates. Mash off—At the end of mashing, when the temperature is raised to about 170°C to inactivate enzymes.

Mash tun—Where the mashing step takes place; may contain a false bottom and be used for wort separation. Oast house—The facility used for drying whole hops. Pitch—The step when wort is inoculated with yeasts.

Trub—The precipitated material obtained from the wort after boiling; it is rich in protein and hop solids.

wet), and only later, when the moisture is reduced, to dry at higher temperatures.

During the drying step, the moisture drops from 45% at the start to about 15% to 18% at the end.The dried malt is then further dried— or "cured" or "kilned"—at temperatures as high as 80°C, and the moisture decreases to less than 5%. At this point the water activity of the malt is usually reduced to 0.3 or lower, so enzymes are well preserved and no microbial growth is expected to occur. At this point, the malt contains mostly carbohydrate and protein (Table 9-1). Finally, the malt is placed in large trucks or train cars for large breweries or packaged in bags and shipped to smaller brewers.

Although the main purpose of the drying and kilning steps is to arrest germination and preserve enzyme activity, another important series of reactions also takes place. It is during kilning that non-enzymatic browning and associated heat-generated flavor reactions occur, which is readily apparent in the malt and espe-

Table 9.1. Approximate composition of malt.

Component

% dry weight

Starch

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