Hops

Hops, Hamulus lupulus, is a truly remarkable plant. Although it originally grew wild, and still does, it is intensively cultivated in a few countries for use only in beer. The major hop-growing countries are Germany, the United States, the Soviet Union, Czechoslovakia, Yugoslavia, and the United Kingdom. Figure 8 shows hops growing in Germany. Hop picking by hand in Czechoslovakia is shown in Figure 9.

The use of hops in beer only goes back some 500 years. Many plants had been used to flavor beer, until it was discovered that hops not only makes beer pleasantly flavored but also controls the growth of spoilage bacteria. The use of hops is now universal in beer.

Hops contain a group of compounds, humulones, which are very insoluble in water, but which undergo a chemical rearrangement during the brewing process to form an isomeric group of compounds called isohumulones. The iso-humulones are soluble in water and impart to beer a

Figure 6. Structure of the linear starch fraction. Each black circle represents a glucose unit, and the aldehydic terminus of the chain is indicated by an asterisk. Interglucose bonding is a-1,4, as shown in the inset, with carbon atoms in the glucose unit numbered in conventional fashion.
through an a-1,6 linkage, as shown in the inset.

palate-cleansing bitterness that provides beer with its unusual property of drinkability. The isohumulones in beer can be readily analyzed, permitting a quantitative measure of their presence and thus of the beer's bitterness. Not many flavor compounds in other foods are so easily measured. A diagram of humulone and its conversion product isohumulone is shown in Figure 10. The analogues of humulone (and isohumulone)—cohumulone, adhumulone, and prehumulone—differ only in the number of carbon atoms in the side chains.

In addition, hops contain a volatile oil containing many odoriferous compounds, some of which survive into the finished beer. Some varieties of hops, such as Clusters and Galena, are used primarily for bitterness, whereas others, such as Hallertau and Cascade, are used for their aroma.

The essential oil of hops is, as in all plant materials, of terpenic origin. The major terpenes are myrcene (1), a di-terpene; humulene (2), and caryophyllene (3) sesquiterpenes (Fig. 11). Oxidation products of these hydrocarbons, such as humaladienone and caryophyllene epoxide have

Figure 9. Hand picking of hops. Source: Courtesy of S. S. Steiner.

Figure 9. Hand picking of hops. Source: Courtesy of S. S. Steiner.

Hops is a perennial vine that grows to more than 20 ft in one season. They are trained to high wires held by long poles. The flowers are mechanically picked and dried in a kiln. Hops are used in several forms. The dried cones, compressed into bales weighing 200 lb, are used by many brewers. In this state, hops must be kept refrigerated. Alter

Figure 10. Humulone and isohumulone.

been found and are probably more important to the flavor of beer.

Also present in hop oil are alcohols, such as linalool and geraniol; ketones, such as undecanone-2; and esters, such as geranyl butyrate. These survive into beer and are important components of the hoppy aroma of some beers.

Figure 11. The terpenes (1) myrcene, (2) humulene, and (3) caryophyllene.

natively, the hop cones can be milled to a powder and then recompressed into pellets. These are easier to use at a brewery, but also need refrigeration. Lastly, the hops may be extracted, with an organic solvent such as hexane or alcohol, or with liquid carbon dioxide, and the extract used. These do not need refrigeration and are popular in tropical countries. A cluster of Fuggle hops is shown in Figure 12. Some varieties of hops grown commercially are listed in Table 3, with the country producing the major quantities indicated.

A typical analysis of hops is shown in Table 4. YEAST

Yeast is a unicellular microscopic organism that is fairly distinctive in being able to metabolize sugars either to carbon dioxide and water, in the presence of air; or to alcohol and carbon dioxide, in the absence of air. It is this latter trait that is used in all alcoholic fermentations.

One genus of yeast, Saccharomyces is used in brewing. But there are two species. One is S. cerevisiae, used in producing ales, and also for making bread, wine, and whiskey. It is a fairly hardy yeast and survives in the atmosphere.

The other is S. carlsbergensis (uvarum) used only for lager beers and found no where else but in breweries. It is

Table 3. Hop varieties (In Order of Acreage Devoted to Each Variety)

United States

Figure 12. A cluster of Fuggle hops. Source: Courtesy of S. S. Steiner.

Europe

Australia

Washington

Galena

Nugget

Columbus

Willamette

Cluster

Chinook

Cascade

Mt. Hood

Perle

Tettnanger Horizon Olympic Golding

Idaho

Galena

Cluster

Chinook

Willamette

Nugget

Mt. Hood

Oregon

Willamette

Nugget

Perle

Golding

Mt. Hood

Fuggle

Tettnanger

Hallertau Magnum (G) Hersbrucker (G) Hallertau Tradition (G) Spalter Select (G) Hallertauer (G) Nugget (G) Tettnanger (G) Northern Brewer (UK & G) Fuggle (UK) Golding (UK & SU) Brewers Gold (UK & G) Styrian (Y & SU) Saaz (Cz)

Hallertau Tarus (G) Spalter (G) Target(G) Huiler (G) Orion (G) Record (G) Bullion (G)

Pride of Ringwood

Note: G, Germany; Y, Yugoslavia; SU, Soviet Union; Cz, Czechoslovakia; and UK, United Kingdom.

Table 4. Chemical Composition of HopS

Moisture

10%

Total resins

17-20%

Volatile oils

0.3-1.2%

Polyphenols

2-5%

Waxes and lipids

3%

Ash

7%

Cellulose

55%

Figure 12. A cluster of Fuggle hops. Source: Courtesy of S. S. Steiner.

temperature-sensitive and does not survive in the atmosphere.

Yeast reproduces asexually and multiplies severalfold during a normal fermentation. Because yeast enters a commercially sterile liquid, wort, it may be reused many times in successive brews without danger of contamination. Beer is the only fermented product that starts with a sterile medium. A photograph through an electron microscope of a dividing yeast cell is shown in Figure 13.

The two species of yeast differ in many biochemical characteristics. Table 5 gives some of these differences.

Figure 13. Dividing yeast cell.

Table 5. Biochemical Characteristaics of Yeast Used in Beer Making

S. carlsbergensis S. cerevisiae

Ferment melibiose + -

Utilize ethanol aerobically - +

Attitude after fermentation Settles to bottom Rises to top

Most breweries have their own strains of yeast and continue to use them indefinitely. Very often a pure yeast culture is maintained and propagated in each plant, or, more often, in the parent plant if the brewery has more than one plant.

Figure 13. Dividing yeast cell.

Table 5. Biochemical Characteristaics of Yeast Used in Beer Making

S. carlsbergensis S. cerevisiae

Ferment melibiose + -

Utilize ethanol aerobically - +

Attitude after fermentation Settles to bottom Rises to top

Most breweries have their own strains of yeast and continue to use them indefinitely. Very often a pure yeast culture is maintained and propagated in each plant, or, more often, in the parent plant if the brewery has more than one plant.

Figure 14. Six-roller malt mill. Source: Courtesy of Wittemann Hasselberg.

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