Chances Occurring In Malting Grains

Carefully selected grain, usually barley, is first hydrated, or steeped (1-4,6-11). Usually this is achieved by immersion in water, but sometimes water is sprayed onto the grain. At intervals the grain-water mixture is aerated by blowing compressed air in at the base. At the end of each immersion the water is drained to waste, and air (which may, to advantage, be cooled and saturated with water vapor) is sucked down through the grain. During each airrest period the downward ventilation, or carbon dioxide extraction, cools the grain, provides oxygen, removes carbon dioxide, and accelerates germination. Typically the grain may be successively immersed in three batches of clean water. Later, water is sometimes sprayed on to adjust the moisture content.

After steeping, the grain, which has started to germinate, continues to grow surrounded by humid air (1—4,6— 10). Rootlets (culms, sprouts) grow from one end of each grain and the embryonic coleoptile, also known as the shoot or acrospire, grows beneath the husk. The grain respires, using oxygen and producing carbon dioxide and heat. Hydrolytic enzymes are formed in the scutellum and later, partly in response to gibberellin hormones from the embryo, in the aleurone layer. These enzymes are released into the starchy endosperm, where they degrade the cell walls, some of the reserve proteins, and some of the starch. At the same time some sugars and simple nitrogenous substances accumulate. Collectively these changes are termed modification. When modification is sufficiently advanced, usually when the acrospire is about 0.8-0.9 the length of the grain (and certainly before it has grown out from beneath the husk) and endosperm cell-wall degradation is nearly complete, the malt is ready to be dried. This green malt (green means undried; it is not green in color) is now kilned or sometimes it is cooked and dried in a drum. In a very few cases the green malt is used directly (it cannot be stored), such as in grain distilleries where large amounts of starchy materials must be broken down in mashes and therefore maximum enzyme survival is needed (1,2). In kilning, the malt is dried and cooked, or cured, to a limited extent in a stream of heated air. This stops germination, produces a stable product, removes undesirable flavors, and gives the malt character (desirable color, flavor, and aroma). When pale malts are being made, the initial airflow is rapid and the air temperature is low to maximize enzyme survival and minimize color formation. As the malt dries, the air temperature is raised and the airflow is reduced without major effects on the enzymes, which are more stable in drier grain. When colored malts are being prepared, the temperatures used are higher and the airflows are less. At first the grain is held warm and moist, conditions that encourage first enzyme formation and then, as the temperature rises, enzyme inactivation, but that also favor the accumulation of sugars and amino acids (1,3,4,8). Later, as the temperature is raised, the sugars and amino acids interact to form colored melanoidins and flavorful, aromatic substances. Because darker malts contain lower levels of enzymes, they must be mashed with pale malts, which provide the enzymes to hydrolyze the starch.

After kilning the cooled malts are dressed, that is, sieved to remove the rootlets, which are sold for animal feed, sieved to remove malt and grain dust and thin grains (1-4,6-10). Barley malts lose only rootlets, but malts from naked (huskless) grains, such as wheat, rye, triticale, and sorghum, also lose shoots, because they are not protected by adherent husks (1). After kilning, pale malts are often stored for about 6 weeks when, for reasons that are not understood, their performance in mashing improves. In contrast, darker malts should be used soon after preparation, so that they do not lose their special flavors and aromas.

Roasted and caramel malts are prepared in roasting drums (1,3,4,8), which fall into two classes: (I) those in which kilned malts are roasted (brown, chocolate, and black malts, which are friable) and (2) those in which green, undried malts are processed (caramel malts in which the endosperms are replaced by hard, barley sugarlike masses).

Thus malting converts tough, raw-tasting, enzyme-poor grain into (usually) readily crushed, flavorful, and, at least in the case of pale malts, enzyme-rich materials that can easily be stored and transported and that when mashed give worts that are suitable for a range of uses, such as the manufacture of beer. However, matter is lost during this process. During the preparation of pale malts, made without additives, the total loss (dry weight) is about 10%, 1% in steeping, 4% as rootlets, and 5% as respiratory losses) (1-4,6-10). The losses incurred in making colored malts can be much greater. Losses may appear to be greater until it is realized that the initial moisture content of the barley going into steep may be 8 to 16%, and the moisture of the finished malt 1.5 to 6%.

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