1 The Technology of Malting

Malting refers to the germination of cereal grains under artificially created or controlled conditions.

The process of germination results in green malt, which must be dried; for this reason, germination is followed by kilning. Once this has been accomplished, the final product is referred to as kilned malt.

The primary purpose of the malting process is to produce enzymes in the kernels. During germination, these enzymes bring about certain transformations in the substances stored as reserves in the grain. The formation of enzymes and their effects during germination should occur only to the extent necessary to carry out the desired function. Too much or too little enzyme activity will have a negative impact on the quality of the final product.

1.1 Malting Barley

A number of different cereal grains can be employed to produce malt (refer to Section 1.9); however, two-rowed barley is best suited for this process if the kernels have undergone consistent growth and uniform development. Barley with multiple rows, the original form of the grain, is not utilized for malt production in Europe to any great extent due to the weak, asymmetrical formation of the lateral spikelets (less space to develop on the ear means they are thin and crooked). Outside of Europe, however, this kind of barley is used in malt production due to its higher protein content and greater enzymatic power, facilitating the use of large quantities of adjuncts in brewing.

Two-rowed barley is divided into two main groups:

1. Upright barley: the spike is dense, wide, and usually stands erect while it is maturing; the individual kernels are arranged, so that they are close together (Hordeum vulgare ssp. distichum erectum).
2. Nodding barley: the spike is long, narrow, and bends, so that the ear hangs during maturation. The kernels are spaced further apart (H. vulgare ssp. distichum nutans).

Several varieties of nodding barley have found use as malting barley. These are primarily planted and cultivated as spring barley. The characteristics of the barley remain quite stable if breeding efforts focus on creating highly productive varieties that are adapted to the cultivation and harvest conditions of either a Continental European or a maritime climate. Additionally, these barley varieties are bred for enhanced resistance to plant diseases (mildew, barley rust, net blotch, etc.) in order to reduce the number of pesticide applications.

Some varieties of two-rowed winter barley have attained a qualitatively high level due to recent efforts in breeding, although how widely they will be available around the world in the coming years will ultimately be determined in part by policy decisions concerning malting barley. Breeding naked barley has not yet become established. This is also the case for procyanidin-free barley (refer to Section 1.1.2.6), for varieties with low lipoxygenase activity, and barley with thin cell walls, i.e., varieties with a lower ß-glucan content (refer to Section 1.1.2.2). The quality of these barley varieties suffers under unfavorable climatic conditions, and they exhibit severe losses in yield compared to normal malting barley varieties.

A single mature kernel of barley can be classified as belonging to one of the two main groups based on the shape of the base of the kernel as well as the shape of the rachilla and the type of hair covering it. In addition to these characteristics, the shape of the lodicules and the spiculation of the inner lateral spinal nerves can be used for varietal identification.

Electrophoresis is one method offering a greater degree of certainty for identification through separation of the prolamin fraction (refer to Section 1.1.2.8). Immunological analysis is also possible. Recently, polymerase chain reaction (PCR) has been conducted in two stages for distinguishing barley varieties and has proven useful for this purpose as well. The advantage of analyzing the DNA in this manner is that the determination is not undermined by the malting process as is the case with electrophoretic methods when the malt is overmodified.

Malting barley is commercially classified and traded according to its provenance and variety. Depending on the climatic conditions and the characteristics of each individual variety, there may be substantial differences in the degree to which a particular variety can be malted and in its value as a brewing grain. For this reason, blending should be avoided.

1.1.1 The Morphology of Barley

The barley kernel, which is the fruit of the plant, can be described morphologically as follows:

1.1.1.1 The Embryo The embryo is the living part of the seed and is situated at the proximal end of the kernel on the dorsal side. It consists of the following structures: the shoot apical meristem (future stalk), cotyledon (seed leaf), and radicles (future roots). Merged with the embryo is the scutellum, which is also affixed to the endosperm and channels nutrients to the growing embryo from there. This function is performed primarily by the scutellar epithelium with its tube-like cells facing the endosperm.

1.1.1.2 The Endosperm The endosperm chiefly consists of two layers of tissue: those containing starch and those containing fat.

The core of the endosperm is made up of cells containing starch embedded in a framework of protein and gum substances.

The cells containing starch are surrounded by a triple layer of rectangular, thick-walled cells known as the aleurone or subaleurone layer. It is composed of proteins and fats. The layer close to the embryo is only one cell thick. A thin layer of empty compressed cells, the depleted endosperm layer, lies between the starchy tissue of the endosperm and the embryo. The contents of the cells in this layer have already been consumed by the embryo.

All biological and chemical changes in the barley kernel take place in the endosperm. As the plantlet develops, the endosperm is broken down to its constituent parts and utilized. Consumption of the endosperm during malting should be kept to a minimum for economic reasons. In this respect, the formation of enzymes and the degradation of structural and support substances take on a singular importance.

1.1.1.3 Tissues Surrounding the Kernel The tissues surrounding the kernel: the husks protect the kernel, which houses the developing plantlet, and consist of the inner husk on the ventral side, the palea, and the outer husk covering the dorsal side, the lemma. Under the husks, barley kernels possess two fused layers, an ovary wall or pericarp, and an inner wall, the seed coat or testa. Both are composed of multiple layers of cells that appear to be fused. The testa is semi-permeable, e.g., water can penetrate the membrane while higher molecular weight substances are retained. In addition, water brings various ions to the interior of the kernel.

1.1.2 The Chemical Composition of Barley

Barley consists of dry matter (80-88%) and water (12-20%). The dry matter contains organic compounds, with and without nitrogen, as well as inorganic components (ash).

1.1.2.1 Starch Carbohydrates, especially starch, are the main component of nitrogen-free organic compounds. Barley contains 60-65% starch (calculated as dry matter). With the help of chlorophyll, CO2 and H2O are ultimately converted to starch under the influence of sunlight, releasing oxygen in the process.

The reason that barley kernels accumulate starch is to create a store of nutrients for the plantlet, which can later be utilized in the early phases of its development. The starch is deposited as granules. They occur in two forms: the large granules are lens-shaped, while the small ones are more spherical. The latter increase with the protein content of the barley, and they are richer in minerals compared to the larger starch granules.

A starch granule consists of two structurally different carbohydrates, amylose and amylopectin. Amylose (normal or n-amylose) makes up 17-24% of the starch. It is usually located inside of the starch granule and consists of long, unbranched chains wound into a spiral configuration. Amylose chains are composed of 60-2000 glucose residues connected through a-14 bonds (maltose bonds). The length of the molecules varies with the molecular weight ranging from 10,000 to 500,000?Da. Amylose turns pure blue with iodine; it dissolves to create a colloidal suspension in water and does not form a gel. Enzymatic degradation of amylose, e.g., by a-amylase and ß-amylase, results in the formation of the disaccharide maltose.

Amylopectin (iso-amylose or i-amylose) accounts for about 76-83% of the starch. In contrast to amylose, it consists of branched chains of molecules, which in addition to the predominant a-14 bonds, amylopectin also possesses a-16 bonds (at a ratio of about 15 to 1). The amylopectin chain branches at approximately every 15 glucose units, on average. This three-dimensional, branched structure is what determines the gelatinization capacity of amylopectin. Encompassing 6000-40,000 glucose residues, the molecular weight of amylopectin ranges from 1 to 6?million Da. Amylopectin also contains about 0.23% phosphoric acid incorporated...