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Introduction About 12,000 years ago, humans discovered how to grow plants and domesticate animals, initiating a process that changed the face of the earth and the lives of nearly every organism that inhabits it. At that time, the human species numbered about 3 million individuals, many of whom ate mainly wheat. After 7,000 years of growing this grain, the population numbered approximately 100 million, and the Egyptian farmer who lived in the shadow of the first pyramids was capable of producing triple the food needed to support his family. At the beginning of the last century, after another 5,000 years of cultivation, 70% of the food energy consumed by 1.6 billion individuals still came from cereals, especially wheat. In 2000 70 per cent of the 2.5 billion tons of dry matter intended to feed 6 billion people consisted of cereals, primarily wheat (21 per cent), rice (16 per cent) and maize (22 per cent), the latter being devoted to a large extent to livestock farms. Although it has lost some position, wheat is still the main source of dietary protein (19% of the total), surpassing foods of animal origin (meat, fish, milk, cheese, eggs, overall (17%) and legumes (soybeans, beans, peas, peanuts, overall (13%). Grinding Grinding is the fundamental step in transforming wheat into flour and its primary goal is to separate the starchy egg white of the kernel from the peripheral parts with the best possible yield. The main milling product of durum wheat is groats, while of common wheat it is flours. The transformation of wheat into flour products involves three fundamental phases: grain cleaning, conditioning and actual grinding. ​ Cleaning It is intended to remove foreign material of a mineral or vegetable nature; it is of great importance and must be conducted with special care, as it can affect the quality of semi-finished and finished products. The various cleaning systems adopted, however, have common devices, such as the suction device to eliminate lighter impurities (straw), the calibration device to separate large grains from small foreign seeds, brushes to clean the grain surface and finally a magnetic peephole and separator device. Conditioning A stage in which the grain is wetted with a sufficient amount of water, to facilitate the detachment of the external parts (integuments) from the floury almond and its breaking. This phase aims to soften the casing to prevent fragmentation and promote detachment, to reduce the hardness of the egg white to facilitate its transformation into flour, and to achieve a degree of starch damage optimal for the different uses. Conditioning is influenced by the amount of water added, the temperature of the treatment, and the length of time the grain rests. With hydration, the grain is brought to 16-17% humidity, with a resting time ranging from 12 to 48 hours. The duration of rest is defined on the basis of the initial moisture of the grain and the degree of greater or lesser friability of the almond. For common wheat, in particular, conditioning is differentiated according to the hardness of the kernels (hardness). Generally, higher amounts of water and times are required for hard grains than for soft grains. Consequently grains belonging to different hardness classes should be ground separately to optimize the milling process. For this reason, the hardness parameter of caryopses is increasingly taken into account in commercial transactions and grain storage. ​ Grinding It consists of two actions: the fragmentation/dissociation of the kernels and the separation of the constituents. The first operation, called breaking, allows the central almond and the external coatings to be dissociated, the dressed groats to be divided and the almond to be reduced to flour; the second ensures the separation of the bran and the coatings based on the grain size and their physical properties. The equipment currently used for grinding wheat is the roll rolling mill, which came into use towards the end of the 19th century. Before the introduction of cylindrical mills, grinding was carried out using balls made up of two cylindrical wheels, one fixed and the other rotating. Percussion mills were also used, equipped with rotary hammers or beaters, still partly used today to finely pulverize different materials in a single stage or regrind milling waste. The cylinder rolling mill normally consists of pairs of cylinders; if the machine comprises only one pair, it is called a simple rolling mill, but normally the most common situation comprises two or more pairs of cylinders, a solution designed to save considerable space. Rolling mills transform wheat grains into flour (from the grinding of durum wheat, mainly groats are obtained, from common wheat, flours) through breaking, undressing and regrinding actions. The breaking mills have the function of breaking and crushing the wheat grains, and of more or less completely detaching the almond, which shatters, from the linings, which are removed in the form of bran. The breaking operation must be conducted gradually, in order to avoid excessive crushing of the cruscal parts which otherwise become difficult to separate. Each breaking operation is followed by a sieving separation operation that allows the products to be classified before being sent to subsequent cylinders. This operation is carried out with the plansichter, a device consisting of a set of sieves placed one on top of the other and subjected to movement in order to ensure a smooth passage of products from one sieve to the other. The sieving fabrics can be of metal or silk, they have square-shaped meshes through which the finer particles of the material to be selected pass, while the larger ones end up being discarded. Rolling mill cylinders are made of cast iron and can be rifled or smooth; the rifled ones are provided with grooves or lines designed to cut and reduce the size of the material introduced, while the smooth ones act by pressure or stretching. The rifled cylinders are constructed of very hard cast iron and of greater strength than that used for smooth cylinders. Cylinders always work in pairs; the elements of a pair act at different peripheral speeds, so there is always a fast and a slow cylinder: if the speeds were equal, the material would simply be crushed. In the case of durum wheat milling, the semolina obtained is separated from the bran fragments still attached to the semolina particles by means of the semolina machine, consisting of inclined sieves subjected to oscillatory movement and a suction system that allows the particles to be separated on the basis of their properties (shape, size and density). ​ ​Properties of the flickers and evaluation methods The products of durum wheat milling, as mentioned above, are groats and granulated; those of common wheat, flours. The definition and characteristics of the different types of flour products are regulated by a specific law (Law No. 580, of July 4, 1967, as amended) that regulates the processing and trade of cereals, flour products, bread, and pasta, establishing the limits of certain analytical parameters. From the grinding of durum wheat, the following are obtained: -“durum wheat semolina” or simply “semolina”, a sharp-edged granular product obtained from the grinding and subsequent abatement of durum wheat, cleaned of foreign substances and impurities; - “durum wheat granulated” or simply “granulated” the product obtained from the grinding and subsequent abatement of durum wheat, cleaned of foreign substances and impurities, after semolina extraction; - “whole durum wheat semolina”, a sharp-edged granular product obtained directly from the grinding of durum wheat, cleaned of foreign substances and impurities; - “durum wheat flour”, a non-granular product obtained from the grinding and subsequent milling of durum wheat, cleaned of foreign substances and impurities. From the milling of common wheat, the following are obtained: - “soft wheat flour” or simply “flour”, a product obtained from the milling and subsequent milling of soft wheat cleaned of foreign substances and impurities. Soft wheat flours can be produced in types “00”, “0”, “1”, “2”. - “whole wheat flour”, a product obtained directly from the grinding of soft wheat cleaned of foreign substances and impurities. The legal characteristics of durum and soft wheat flour products marketed in Italy are reported on the side. The parameters considered are essentially humidity, content in mineral substances (ash) and proteins. The maximum humidity allowed for all glazed is 14.5%. The mineral content of a semolina or flour can be considered an index of its purity, that is, contamination by the peripheral layers, since the external layers of the grain are particularly abundant in mineral substances and that, on the contrary, the amylaceous endosperm contains only low levels. The chemical-physical characteristics of the various constituents of the caryopsis determine the quality of the floured products and therefore of the finished products. The qualitative characterization of the flickered products requires chemical-physical and rheological analyses. The latter are analyses that are generally carried out by simulating, with specific tools, the behavior of the doughs during the processing. Chemical-physical analyses allow us to determine the components of the kernels and the floureds (ash content, protein content, gluten content, amylose/amylopectin ratio, lipid content, amino acid composition, etc.) and the texture of the kernels (hardness or hardness). Rheological analyses allow us to evaluate gluten quality (gluten index, sedimentation index, Chopin alveograph, Brabender farinograph, extensograph, etc.), enzymatic activities (Hagberg drop index, amylographic test, etc.), experimental baking and pastification tests. Some of the most widely used methods for the qualitative characterization of flours and groats are briefly described below, excluding chemical analyses. ​ ​Hardness or hardness of the kernels. It can be determined by measurements of the grain size of the wholemeal flour or flours according to the PSI (Particle Size Index) or NIR (Near Infrared Reflectance) methods. Another method, proposed more recently, is based on the evaluation of the resistance that kernels resist to crushing (Single Kernel Characterization System, SKCS). Results are generally expressed by an index in the range 1-120 that increases as hardness increases. Sedimentation volume. It is a method that allows to evaluate both the quantity and quality of wheat proteins and is based on the swelling and flocculation characteristics of the proteins in a lactic acid solution. There are numerous versions of this method, the most widely used being the Zeleny test and the sedimentation volume in SDS. The results are expressed in ml with a value that increases proportionally to the improvement of the qualitative characteristics. Gluten content. The amount of gluten is determined starting from the palinate (semolina or flour), which is kneaded with a 2% sodium chloride saline solution and subsequently washed with water in order to eliminate starch and soluble proteins. The wet gluten thus obtained can be dried in an oven or with appropriate drying plates. The result is expressed as a percentage as both wet gluten and dry gluten. Gluten index. It is a method that allows you to evaluate the quality of gluten. The extracted wet gluten is subjected to centrifugation and forced to pass through a special sieve under controlled conditions. The percentage of gluten that remains on the sieve after centrifugation is called the gluten index. If gluten is very weak, it passes entirely through the sieve and the gluten index is 0; conversely, if gluten is very strong it does not pass at all and the gluten index is 100. Hagberg fall index or Falling number. It is a method that allows to highlight grain defects due to pre-germination of the kernels and therefore high presence of α-amylases which make the doughs sticky. The drop index provides indications of the viscosity of a flour suspension in water. The result, expressed in seconds, is inversely proportional to the α-amylase content. Chopin's alveographer. It allows us to evaluate the behavior of the dough, obtained with fixed hydration, when it is subjected to deformation by blowing air which transforms it into a bubble until it causes it to break. Simultaneously with these transformations, a path is produced from which various information can be obtained. The area under the path indicates the resistance offered by the dough to deformation, therefore the strength of the flour (W); the height of the curve represents the toughness of the dough (P); the length of the curve represents its extensibility (L); the ratio between toughness and extensibility expresses its equilibrium (P/L). Brabender's Farinograph. It measures and graphically represents the variations in consistency of a dough produced by different mechanical stresses during the kneading phase. Water absorption (%) represents the maximum amount of water that can be absorbed by the flour to produce a dough with optimal consistency. The development time (min) represents the time required for the flour to absorb the optimal amount of water and bring the dough to the optimal consistency. Stability (min) represents the time in which the flour maintains optimal consistency conditions; it follows that long stability times correspond to strength characteristics of the flour, which ensure high resistance to processing and leavening. The degree of drop (UB) expresses the loss of consistency of the dough after a predetermined interval of time. Baking test. It allows to represent the bread-making quality of the grains in the most complete way. The most widely adopted method internationally (AACC 10-10B) allows to evaluate the volume and height of small cassette loaves obtained from 100 g of flour. Bread volume is highly correlated with all parameters derived from chemical-physical and rheological analyses. Pastification test. It is carried out on pilot plants, therefore using limited quantities of material (2-3 kg of semolina), obtaining indications on the quality of the finished product (pasta). The resulting pasta is then cooked under well-defined conditions and evaluated based on three parameters: stickiness, nerve, and massing. The evaluation is generally done with an organoleptic test. ​ Industrial use In the case of durum wheat, almost all of the flour products are intended for pastification, as durum wheat groats are the raw material of choice for the manufacture of food pastes; soft wheat flours can also be used for this purpose, but produce lower-quality products. In the case of common wheat, flour products are used for a variety of products, therefore the intended use is established on the basis of the quality characteristics of the flours. In order to respond adequately to the varied demands of the industry for the first and second processing of common wheat, the need to differentiate the grains according to their intended use by using certain quality indices deemed to be of fundamental importance has long been felt. The classification provides for the identification of five classes, each of which makes precise reference to the intended use of the product: strength wheat (FF), top bread-making wheat (FPS), bread-making wheat (FP), biscuit wheat (FB) and wheat for other uses (FAU). The intended use of soft wheats is therefore defined on the basis of the rheological and technological characteristics of the flour products, as well as some chemical parameters. In order to enhance the quality of national production, in the absence of official standards, voluntary standards (UNI standards) have been prepared for the classification of hard and soft wheats and their processed products. ​