magazine

Introduction Corn, of all agricultural raw materials, is the one that has been able to adapt more than any other to different agronomic environments, representing an irreplaceable source for direct use and industrial transformation.  The changing primary dietary needs, combined with the development of new knowledge in the chemical and microbiological fields, as well as the acquisition of increasingly sophisticated industrial technologies, have allowed, since the mid-18th century, corn to be considered the preferred material for industrial use. This is how, thanks to its chemical-physical properties and high caloric power, intuited more than four thousand years ago by the peoples of Central America, numerous industrial activities have developed capable of exploiting and enhancing the properties of this wonderful “green mine”. Among these, the main ones are wet starch extraction and its use in the milling industry and green chemicals, which use corn for renewable energy production and to replace plastic materials with biodegradable products. ​ ​From Corn to Starch: The History of Starch from Its Origins to Today The starch extraction technique has been known since ancient times when it was obtained from a mixture of wheat and barley flour. The discovery of ancient Egyptian papyrus sheets dates the use of starch to 3,500-4,000 years before the coming of Christ: at that time, rice and wheat were widely cultivated and were used not only for human consumption but also for technological purposes, following the path of civilization. In the first century AD, the Greek scientist Dioscorides, in his treatise on substances with beneficial effects on human health “Perí haplón pharmákon” (Treatise on Medical Practice), was the first to speak of a substance of plant origin used for the production of medicines and household uses, not exclusively for food. The Romans were initially and subsequently credited with improving and spreading the technique of extracting starch from cereals, which remained almost unchanged until the late Middle Ages. The modern history of the wet-mined starch industry developed at its origins in the United States, where, in the early 19th century, starch was obtained from wheat and potatoes. The credit for the birth of the first corn starch mill is commonly given to Wm. Colgate & Company, which converted the existing plant in Jersey City, NJ, where wheat was previously processed, to corn: it was the year 1844.  From this moment on, the great diffusion of starch in the United States began, and corn soon became the raw material par excellence. The use for bouzzima, as an adjuvant in the spinning of plant fibres and the packaging of fabrics, as a sizing represented the first significant commercial outlet for starch. In the same years, starch extraction from wheat and potatoes was taking its first steps in Europe. The production in 1866 of dextrose, a simple sugar that represents the basic element of the complex starch molecule, marked an important moment from which it took its first steps and then the chemistry of sugars developed: dextrose soon became the privileged energy support for the fermentation industry. In the years that followed, the starch hydrolysis technique was refined, allowing the production of sugar mixtures intended for a wide variety of uses, especially in the food sector, acting as sweeteners replacing cane sugar.  When starch extraction takes place on an industrial scale, starches begin to valorize all those “fatal” products which, being like starch also constituents of the corn kernel, are separated during the subsequent starch separation phases. This is how the pericarp, a thin coating layer of the fiber-rich kernel, gluten, which represents the protein fraction, the germ with a high oil content, and the maceration water rich in soluble elements, find their natural outlet in the livestock feed and fermentation sectors. Only at the beginning of the 1900s did starch chemistry develop, capable of fully exploiting and enhancing its main rheological characteristics such as viscosity and fluidity. After developing technologies capable of raising purity levels, the production of roasted starches, dextrins, cold-soluble pre-cooked starches, and chemically modified starches begins. In the 1920s, microbiological research gave a major boost to the sector, introducing the use of enzymes capable of acting in a targeted and specific way on the starch molecule for the manufacture of the first hydrolysis products, crystallized dextrose and therefore anhydrous (dehydrated) dextrose and maltodextrins. The possibility of producing purified and crystallized dextrose, together with the availability of new and more efficient enzymes, subsequently allowed the manufacture of isomerization products such as fructose mixed with dextrose from isoglucose, sucrose substitute, beet and cane sugar.  Thanks to high purity standards, corn syrups have therefore contributed to the exponential growth of the fermentation industry for the manufacture of yeasts, enzymes, organic acids, productions very often integrated downstream of the starch industry. In parallel with the evolution of sugar chemistry, the transformation of starch was refined in the second half of the twentieth century, which allowed us to differentiate the supply of chemically and enzymatically modified products. The doors have therefore opened wide for the use of starches in the food, pharmaceutical, industrial (foundries, spinning mills, cement factories, paints), paper and cardboard sectors and only more recently has it been used for the production of biodegradable plastic materials. The search for maximum efficiency in plant management, linked to ever-increasing economies of scale, saw the development in the United States, in the post-war period, alongside starch manufacturing, the production of ethanol manufactured directly from corn or its hydrolysis products (corn sugars). Only recently in Europe has there begun to be talk of ethanol production from maize and wheat, a decision which, because of the high prices of the raw material, is now being called into question. Corn, on the other hand, continues to represent the main raw material for starch making, as corn starches and their derivatives are destined to be used in a myriad of applications in the most disparate fields. ​ Corn caryopsis Before delving into the various processing stages that are carried out in a wet corn extraction industry, commonly called “stew”, it is advisable to briefly put the corn kernel under the magnifying glass, highlighting its conformation, composition and the main properties of the elements that compose it. Water solubility, specific gravity, density, and hydrophobicity are specific properties of each of the elements present in the grain, fundamental characteristics for carrying out the separation and purification processes of the components extracted from the grain. ​ What is starch Starch is the main energy storage material present in the plant world. Cereals (corn,wheat, barley, rice together with potato tubers and tapioca) represent the primary source of starch found in nature and used for industrial purposes. Visually, starch molecules appear to vary in shape depending on their origin: by observing them under a microscope and using a contrast solution, polyhedral structures typical of corn can be identified; rounded shapes of irregular size are characteristic of wheat starch. The lenticular-looking granules distinguish potato starch commonly referred to as starch. For simplicity, the starch molecule can be compared to a ball of yarn in which filaments made up of a linear sequence of dextrose molecules called amylose are rolled up, which are opposed by branched chains called amylopectin. Amylose and amylopectin are arranged radially in the granule and are therefore kept cohesive by the presence of a dense network of chemical bonds. Commonly the starch contained in cereals is formed of about 15-25% amylose and 75-85% amylopectin. It is interesting at this point to remember that starch is not soluble in water due to the particular structure of its granules in which the tangential arrangement of the hydrophobic terminals is observed which, having no affinity with water, make it insoluble. To solubilize it, it is necessary to disperse it in water and therefore, following heating to a temperature above 60/70°, a dense suspension is formed in which the filaments that make up the starch granule space apart, allowing the insertion of water molecules: the so-called starch weld is then formed.   The presence of water inside the granule is temporary and unstable: following the subsequent cooling that follows the cooking and the relative bursting of starch, the water is expelled from the solder and chemical bonds are reformed, especially between the amylose filaments. This phenomenon is known by the term retrogradation.  Each type of starch, depending on its botanical origin, has its own cooking temperature and a specific response to the heating and subsequent cooling cycle, which is ultimately expressed in the different level of retrogradation. Waxy maize starch, for example, thanks to its high amylopectin content (99.8%) is able to stabilize the water absorbed during heating and therefore has a very low level of retrogradation. A further characteristic of amylopectin is represented by the ability to complex iodine: it follows that if waxy corn starch is sprayed with an aqueous solution of potassium iodide, the red color of the contrast liquid remains evident. In contrast, in the case of common corn starch, the presence of amylose causes a dark blue, almost black coloration to appear, the same as that observed on all other types of starch. The iodine test is commonly employed to verify in a simple, but certain way, the purity of the waxy starch and the grain from which it is obtained. The behavior during cooking and subsequent cooling is very important for characterizing the rheology of native starches, obtained from individual raw materials. Using the Brabhender analytical method, the change in viscosity of the starch weld is monitored by describing a typical path for each type of starch. As can be seen in the graph on the side, the Brabender records the viscosity changes in the individual phases of the cooking cycle: it starts with the initial heating (A), followed by the swelling and bursting of the starch granules (B), and ends with the viscosity drop resulting from the cooling of the starch weld (C). Thanks to precise chemical treatments, it is possible to modify the behavior of the starch at different stages of cooking, thus describing modified paths compared to those specific to native starches. In any case, the initial characteristics typical of the individual materials being worked on remain fundamental, enhanced thanks to the chemical modifications made. In addition to viscosity, there are also other rheological characteristics that characterize the different raw materials, which are reported in the following table. ​ Quality of maize used by the starch mill The production process carried out in the starch factory is well suited to corn, which therefore represents the most important part of the raw material used. Alongside common corn, the so-called special corn (waxy, amylo-corn) are also used, to a lesser extent than common corn, but very interesting in relation to the respective rheological characteristics of its starch. Alongside these, for some processes, white corn is used, interesting for its natural characteristic linked to the white color of the kernel due to the absence of xanthophyll (yellow pigment), which allows the production of completely unpigmented starch defined as extra-white. All special types of maize share the characteristic that the gene determining the single specificity is recessive: it follows that, in the case where the egg of one of these maize is fertilized by a pollen grain from a normal plant, it loses its original nature, giving rise to a polluted kernel. Since these are recessive genes that are expressed quantitatively, recessiveness manifests itself punctually on each caryopsis, characterizing all the starch it contains. It follows that it is possible to find all pure kernels on the same ear or, in case of contamination with foreign pollen, 100% pure kernels can coexist, alongside others whose starch is completely contaminated. The number of contaminated kernels in relation to the total number present on the ear indicates the level of pollution of the corn. By commercial convention special corn is deemed pure when pollution does not exceed 2% for white corn and 5% for waxy and amylo-corn.  The existence of these genes in nature has been known for centuries, but only as a result of the development of starch and in accordance with the need to identify new types of starches for technological use have researchers developed specific Mendelian genetic improvement projects to enable their production on an industrial scale. Turning to the aspect related to industrial use, it is essential that special corn be pure, that is, free from contamination due to foreign pollen. Production must be carried out in scrupulous compliance with certain precautions: – use only pure seeds; – use machinery for sowing, harvesting, drying, storing, and transporting perfectly clean from other corn, avoiding the causes of any occasional contamination; – sow only “isolated” plots, that is, distant from fields cultivated with other types of corn in order to prevent contamination by foreign pollen. That is, the same rules must be adopted for the production of hybrid seeds. Processing into starch represents, for waxy maize and amylo-maize, the only use that justifies their production, providing a certain market outlet for producers. These special corn, together with white kernel corn, are grown on the basis of a supply chain contract concluded before sowing with the processing industry. In light of scrupulous compliance with specific specifications, aimed at production in isolation and in purity, a price differential is recognized, provided that the consignments meet the required quality standards. Except for the purity of special corn, processing into starch does not require additional characteristics of the corn: commercial quality, understood as “a healthy, fair, and marketable commodity” in compliance with current health regulations, fully meets the needs of the starch industry. The quality of the grain is checked promptly upon entry into the factories in order to verify compliance with commercial parameters. The obligation to comply with national and EU legislation on the health and health of food also requires that processed corn be free from fungal (aflatoxins and more generally mycotoxins), chemical (plant protection products), and radioactive contamination. From a health perspective, corn quality is closely related to proper agronomic practices, starting with the choice of hybrids appropriate to the environment in which they must be grown in the absence of stress and kept free from parasitic attacks, and the correct and timely completion of subsequent harvesting, drying, and storage operations. In addition to the traditional contractual criteria for controlling the raw material, the starches have an internal control method, the promatest, used to verify the quality of the corn to be used. This is an analytical method that, by quantifying the denaturation of proteins caused by poor drying practice, allows us to predict, by analyzing a representative sample, the quality of the corn that will be processed in the plant. Taking into account the capacity of a starch factory, which in Europe can vary from 1000 to 2000 t of processed corn per day, promatest has significance when it is carried out on representative samples of large homogeneous batches of corn, as is the case for example in France, where a large part of production is concentrated in large collection centers. On the other hand, it appears to be of little practical interest, because it is not representative, in the event that the supply of maize is fragmented, as happens in Italy. In order to adequately respond to the needs expressed by the food sector regarding the “non-derivance” of starches and their derivatives from genetically modified maize, European and Italian starches in particular have implemented certified procedures for the traceability and traceability of starches and derivatives obtained exclusively from conventional maize. ​ Wet steelyard workings The processing of maize into starch represents the typical industrial cascade process, in which the result of a single processing stage can be at the same time a finished product intended for sale or raw material for subsequent industrial stages. In any case, at the end of the production process, the starches and derivatives obtained constitute the raw material for use in various industrial sectors and only in very limited cases (such as for coproducts for livestock use) are they themselves finished products. An important aspect lies in the fact that nothing is lost of the components of the corn kernel: all its constituents are extracted, isolated and find useful use. Most of the processing is carried out in an aqueous environment and at high temperature conditions, thanks to the use of steam: it follows that, in addition to using large quantities of agricultural raw material, the starch also requires the use of high volumes of water and a very significant consumption of energy, not only for the operation of the machinery, but also for the production of steam, for the evaporation of water, up to the drying of the finished products. To give an idea of the energy needs, just think that the electricity demand of an average plant processing 1500 t of corn per day is comparable to that consumed by a town of 20,000 inhabitants. Going into the details of the production process, we first proceed to the careful screening and cleaning of the grain, with the aim of eliminating all impurities and small fragments: only the almost intact kernels are intended for processing. The first real stage of the process takes place in a humid steelyard where the corn is left to macerate in water for more than thirty hours at a constant temperature above 50° C. The purpose of maceration is to soften the grain to make its subsequent separation possible, while recovering all soluble elements. The separation is also facilitated by the use of reduced quantities of sodium bisulfite: an osmotic exchange allows the diffusion of soluble materials from the kernel into the maceration water, enriching it with mineral salts, amino acids, proteins and lactic acid (formed naturally thanks to the establishment of a lactic fermentation of the free sugars present in the grain), leading overall to the formation of the so-called corn steep liquor. At the end of the maceration, the corn steep liquor is separated and, after being concentrated and sometimes atomized, is ready for marketing. A significant portion is also added to corn semolina to increase its protein content, forming corn glutinate flour or corn gluten feed. The grain, after being separated from the maceration water, is sent to large plate grinders which, in an energetic but delicate way, mash the corn while preserving the integrity of the germs and transforming everything into a thick slurry. The mechanical separation phase of corn then begins, during which the different density and specific gravity characteristics of the caryopsis constituents are exploited. The germs are very light given their high oil content. Therefore, thanks to the use of large hydrocyclones, they are separated first since they are located “floating” on the suspension consisting of starch milk, gluten and bran. By injecting this suspension into the apical part of the hydrocyclones and thanks to centrifugal force, a vortex is generated in which the lighter parts, i.e. the germs, are pushed upwards to be extracted. The germ is then washed repeatedly and the excess water is removed, before proceeding to drying. The germ thus conditioned is ready to be squeezed or, alternatively, treated with solvents to extract the oil, obtaining as co-products respectively germ cake or corn germ extraction flour, used in animal nutrition. The next processing step involves separating the bran (the pericarp, i.e. the external part of the caryopsis) from the starch and gluten milk, carrying out subsequent passes through sieves, interspersed with repeated washing. A light pressing of the germ is then carried out to remove excess water and allow the addition of the concentrated corn steep liquor that had been separated previously. After drying, the semolina is ground and conditioned to also be used in the livestock sector. Finally, the proteins are separated from the starch using flat centrifuges. The proteins, which have a lower density and which float on the denser starch milk, are refined by outcrop (overflow) through successive passes on flotation crates. The excess water is then removed by using drum filters that operate in a vacuum. Drying and conditioning conclude the processing of proteins which are then intended for animal feed. At this point, after isolating the maceration water and recovering the germ, sifting the semolina and extracting the gluten, all that remains is to deal with the starch milk. First of all, it is necessary to repeat the washing of the starch milk several times through a countercurrent step process with drinking water, in order to reduce the protein content from the original 2-4% to the final 0.3-0.4%. The search for the purity of starch milk is fundamental, given that the outcome of the subsequent technological applications for which starches and their derivatives are intended depends on it, with particular attention to corn syrups and sugars: that is, the aim is to prevent the residual presence of proteins that can cause the syrups to brown, degrading their quality, when they are heated due to the onset of the well-known Maillard reaction. It should be remembered that there is a direct correlation between the separation of starch from proteins: if corn is dried under suboptimal conditions, the protein fraction is glued to the amylaceous fraction. Centrifugation of part of the pure starch milk in cloth filters therefore allows the starch to be dried in a hot air stream and ground, a prelude to final conditioning for sale, as native starch. The most significant part of starch milk represents the raw material for further processing, carried out in the downstream departments of the wet starch factory for the production of modified starches, corn syrups and sugars, hydrogenated products, organic acids, etc. ​​ Starches obtained from maize Concentrated and purified starch milk is the raw material for the production of various types of starches. Native starch. This is starch in its natural state, as it was extracted from corn without undergoing any treatment: it is obtained directly by centrifuging starch milk and dried in a stream of hot air. Native starch is used as an ingredient in baking, as a thickener in the food industry (puddings, creams, and desserts), or as a base for glues in the paper industry. Pre-cooked starches. Starch by its nature is insoluble in cold water: to make it soluble it must be cooked before being dried. The starch milk is then heat treated at a temperature above 120 °C, generated by steam under pressure. The starch milk suspension at high concentration levels is then poured onto a drum which, thanks to counter-rotating rollers, creates a dough that is simultaneously cooked and dried. The resulting sheet is then finely ground before being conditioned. The product obtained is a cold water soluble powder. With a heat treatment of the starch, a reduced water content and in a slightly acidic environment it is possible to toast the starch obtaining the dextrins which find natural use as a basic element for the production of glues and sizing. These dextrins, normally called “yellow dextrins” because of their characteristic straw colour, should not be confused with maltodextrins, which are used for food. Modified starches. Starting from native starch, a series of transformations of an exclusively chemical nature can begin aimed at the production of modified starches. This category includes: – fluidized starches. The fluidization treatment, which takes place in an acidic environment at a temperature above 40°C, aims to reduce the viscosity of the starch and increase its fluidity, making it more easily usable at high dry matter concentrations, as required in the formulation of glues for the preparation of corrugated cardboard or for the formation of drywall. – etherified and esterified starches. They are obtained by inserting chemical dinature groups on the starch chain. In the case of etherified starches, by providing positive charges, the so-called cationic starches are formed which, by interacting with the anionicity (negative charges) of the cellulose fibres, improve the strength and general characteristics of the paper. In view of the different chemical reagents used, the esterification reaction allows the manufacture of acetylated and crosslinked starches. The modified rheology of these starches is able to express high resistance to chemical attacks and mechanical stresses, thus stabilizing the starch solder during its applications mainly in the food sector, for example for the production of pre-cooked foods. It is also possible to produce starches capable of combining two or more of the aforementioned chemical modifications, allowing starch to be attributed emulsifying properties. – Dietary fiber. By subjecting native starch to a dextrinization treatment under tightly controlled conditions, a repolimeration process is carried out that leads to the formation of new structures that are resistant to enzymes from the human midgut tract but are able to ferment in the subsequent colon tract. Soluble dietary fiber is used in practically all those food products in which it is intended to increase the fiber content in order to improve digestive function, sometimes entering into the formulation of particular foods. ​ ​Corn syrups and sugars Starch milk is liquefied under the action of acids and/or enzymes, meaning its chain is cut into pieces of various compositions, giving rise to mixtures of sugars. This type of intervention is exactly the opposite of what nature does. In fact, the plant polymerizes the simple sugars obtained at the end of the photosynthetical process, leading to the formation of starch. Two enzymes are used for starch hydrolysis: α-amylase, which roughly breaks the glucoside chain making starch soluble, followed by the action of ’ amyloglucosidase, which pushes the separation up to the single monomer, i.e. glucose. At the end of the various hydrolysis processes, the enzymes are thermally deactivated. The resulting sauces are filtered and purified by passing them through filters of fossil flours, ion exchange resins, and activated carbons, in order to eliminate any residual impurities and make the resulting solution perfectly transparent and odorless. After being concentrated, corn sugars can then be marketed. The sweetening and organoleptic properties are a direct function of the degree of hydrolysis and the related level of dextrose equivalent. It follows that, for the same dry matter and at low levels of hydrolysis, syrups are viscous and not very sweet. Pushing the hydrolysis until dextrose is produced progressively increases the viscosity and with it increases the sweetness.  All sugars are distinguished by a proper number of equivalent dextrose (DE), which identifies the degree of hydrolysis achieved compared to that of dextrose which, by convention, is taken equal to one hundred, the monomer being the result of the total hydrolysis of starch. Through the procedure described above, mixtures with different levels of hydrolysis and therefore of viscosity and sweetness are produced, depending on the type of final use. For fruit candying, for example, a viscous and not too sweet product is required; conversely, in the packaging of canned fruit, ice cream, or soft drinks, sweetness is preferred. The corn syrups also include hydrols, starch syrups that do not have very high levels of purification. These are intended for use in the fermentation industry, competing directly with beet and sugar cane molasses. Not all syrups are marketed,and a significant portion are sometimes used as raw materials for subsequent processing, within the same starch factory, for the production of organic acids, yeasts, or even ethanol, as often happens in the United States. Maltodextrins. By operating only a slight attack with inorganic acids, maltodextrins are produced, characterized by the presence of maltose (dimer consisting of two dextrose molecules) and a low level of DE, less than 20; furthermore, they do not crystallize easily and are fermentescible. These chemical-physical characteristics determine its widespread use in baby products, sports drinks and foods, sausages, sauces and food soups. Dextrose. By pushing the enzymatic process with amyloglucosidase to the maximum, the starch is completely hydrolyzed, thus obtaining dextrose, the basic constituent of starch. Through the subsequent purification and crystallization process, powdered dextrose is obtained, and by reducing the water content to the crystallization level alone, anhydrous dextrose is obtained. This is widely used in the food industry where, in addition to its sweetening value, it is used as a humectant to promote the ripening and preservation of meat. Under strictly controlled production conditions, solutions of non-pyrogenic dextrose are also produced, used as an excipient and energy in physiological solutions injectable into a vein. Isoglucose. By acting isomerizing enzymes on dextrose, it is possible to obtain fructose which, in a 42% mixture with dextrose, constitutes isoglucose, a liquid sugar sweetening sucrose substitute (beet or cane sugar). The fructose content can be raised up to 55% by enriching the isoglucose by chromatography, a very energy-intensive process. This practice is widespread in the United States where isoglucose “55” is the preferred sweetener for the manufacture of carbonated beverages, such as cola. The main use of isoglucose is through its incorporation into soft drinks and fruit nectars. Its use remains limited in Europe due to Community legislation that quotas its production by tying it to production quotas. In contrast, in the United States, isoglucose (HFCS-High Fructose Corn Scyrup) is by far the most widely used sweetener. Polyols. The production process involves the hydrogenation of simple sugars (dextrose, fructose) or dimers (maltose), a reaction that occurs in a catalyzed environment and under rigorous control. The products obtained, called polyols (sorbitol, mannitol, xylitol etc.), constitute the category of natural sweeteners (sweeteners) and are characterised by a reduced caloric power (2 Kcal/g) compared to that of sucrose (4.1 Kcal/g). They are also acariogenic, as they are not fermented by bacteria naturally present in the mouth. It follows that polyols are widely used as sweeteners or simply for sugar-free confectionery in candy production and chewing gum. The particular rheology towards water also allows its use as humectants and stabilizers in the cosmetics industry, which incorporates very large volumes of sorbitol into toothpaste. Sorbitol itself is able to stabilize the humidity of cigarette tobacco. Cyclodextrins. Cyclodextrins are manufactured following a highly technological process thanks to the action of cyclizing enzymes acting on maltodextrins that have previously undergone a liquefaction process. Enzymes are able to organize maltodextrine molecules in a cyclic form, forming a ring capable of mechanically including molecules whose size is compatible with the empty space inside the cyclodextrin itself. Depending on the number of molecules that make up the ring, we have α-cyclodextrins with six glycopyranose units, β-cyclodextrins with seven units and γ-cyclodextrins with eight glycopyranose units. Because they are insoluble in water, cyclodextrins can bypass medicinal ingredients through the first tract of the human digestive system, while being fermented by the bacterial flora of the colon. They can also delay the release of flavorings in chewing gum, slow oxidation, or simply mask the unpleasant aroma of cod liver oil, intended for oral administration and lastly as an odor capture for domestic environments. Coloring caramel. Treatment at elevated temperatures above 160-170°C of concentrated glucose syrup induces browning of the solution resulting in the production of caramel. Depending on the treatment conditions (temperature and salt charge), it is possible to modify the color intensity of the finished product. Caramel, a natural colorant, is widely used in the confectionery industry, soft drinks, spirit drinks, beers, and vinegar. Corn in the milling industry Grinding for the production of food flours represented the first ever processing of corn. The milling technique has evolved greatly over the centuries: it has gone from grinding in mills powered by the energy of draft animals to subsequently exploiting the power of the water and wind captured by the mills themselves. The processes carried out in modern plants allow for the best use of the physical characteristics of the grain, obtaining, with desired precision, a wide range of products intended for human nutrition, fermentation, and animal nutrition. The goal of mill processing is to mechanically crush the caryopsis, in order to selectively separate the germ and bran from fractures of different calibers, while limiting the formation of flickers. All types of corn can be used in mills; however, it is preferable to use varieties with vitreous fracture, which better respond to mechanical stresses, allowing for better manufacturing yields and ensuring the production of finished products suitable for subsequent industrial applications. There are various techniques that can be used to grind corn, but they can all be traced back to two general principles: dry processing and processing with prior hydration of the grain. First of all, it is necessary to proceed with the careful screening and cleaning of the corn to eliminate all impurities and any foreign corpuscles. The cleaned corn is then sent to the degerminators who mechanically determine the clear detachment of the germ, thanks to the elasticity of the latter which contrasts with the compactness of the vitreous part, and the friability of the floury part of the kernel. After an initial selection of the fractures obtained as a function of grain size, the larger ones are restarted at the rolling mills to be treated again. The passage on tarare and on densimetric tables allows to isolate the germ and the vitreous fractures from the floury part and from the bran. The glass fractures are then ground by roller mills (rolling mills) until they reach the desired grain size, allowing the production of coarse-medium-fine broken pieces, beer gritz, polenta semolina and livestock flour. The separation of the germ, combined with the calibration of the glass breaks, occurs thanks to its different specific gravity. The germ is then subjected to further mechanical purification in order to separate the last residual impurities and be sent for oil extraction. In addition to the dry mill processing scheme, more sophisticated techniques are adopted that involve resorting to different levels of preventive grain hydration to allow the manufacture of different types of finished products, a process that has nothing to do with processing in a starch mill where the separation of the corn involves prolonged maceration.  The addition of water is aimed at softening the grain, which occurs over the course of 8-10 hours and gives greater elasticity to the germ, facilitating the detachment of the pericarp. The final passage through the planesicher channel (a machine used to separate the ground products from the rolling mills, dividing the flour from the bran) is used to classify the following products: – hominy gritz: broken products of a caliber between 5700 and 4000 microns; – corn-rice: broken rice substitutes (3160-1000 microns), used for human consumption in Southeast Asia; – broken pieces of various grain sizes. Depending on the different processing techniques, whether dry, wet, or semi-wet, different production balances can be drawn up, in addition to obtaining finished products with different characteristics, which determine their use in the various sectors. The production of corn flour, whether braised or foil, is intended for the preparation of polenta or for baking. This remains the most common employment. The evolution of tastes and consumption linked to the intrinsic properties of corn, which represents an important source of fermentescible carbohydrates, has led the milling industry to modify the nature of its finished products according to new application needs.  Pre-cooked flours have thus joined the traditional craving, which can be cooked in just a few minutes and which respond effectively to the accelerated rhythms of modern times. The same pre-cooked, highly digestible flours are used in baby foods and baby weaning foods. In recent years, the market for corn-flakes, products rich in fiber, consumed mainly for breakfast, has developed. The coarse husked corn stews are previously mixed with water, flavorings, malt, and various additives before being cooked in an autoclave. After a resting phase, which can be extended for up to 24 hours, they are laminated, dried and then packaged. The high total starch content, approximately 70%, makes corn the preferred cereal as a raw material for fermentations and, in particular, for the production of alcoholic beverages such as whisky, gin, rum, vodka, etc. The use of degerminated corn stews in this field of application allows for high yields, up to ’82-83%. Granulated corn gritz blends (250-1250 microns in size), with approximately 35-40% malt, are the basic recipe for brewing beer. Starch and green chemistry Starch plays an important role in the “green chemistry” sector, which identifies that set of activities that process agricultural raw materials with the aim of progressively replacing dangerous, toxic and polluting substances, in accordance with the European strategy of developing eco-sustainable industrial activities. Starch can therefore be fully defined as a biorefinery that, to produce starch, uses exclusively renewable raw materials such as corn. Starch, as we have seen, is a perfectly biodegradable polymer that presents itself as a valid alternative to the use of products that are largely usually obtained from raw materials of fossil origin. Through fermentation processes, citric acid, lactic acid, organic acids, enzymes, yeasts and ethanol are produced. Chemical processes produce resins, biodegradable plastics (polylactates), textile fibers alternative to polyesters, biodegradable solvents, lubricants, solvents, pesticides, car tires, adhesive bands, glues, as well as drugs, mulch films, etc. ​ Biodegradable plastic  Biodegradable plastics represent a clear example of how corn, through the use of its own derivatives obtained in the starch industry, plays a fundamental role in the widespread use of environmentally friendly, easily compostable and fully recyclable products. Dextrose, a simple sugar obtained from the hydrolysis of starch, represents the raw material for the creation of a natural fermentation process that leads to the production of lactic acid, an organic acid found in nature at the end of numerous biological processes. Thanks to a subsequent crystallization process, it is possible to eliminate water, a preliminary step for a subsequent polymeration process, which leads to the formation of polylactates (PLA and PHA). These products, after other industrial processes, can give rise to resins or fibres of various appearances, flexibility, plasticity and strength. Biodegradable plastics are widely used in the production of organic waste containers, shopping bags to replace pulp paper, food film and packaging, and various utensils. Further and increasingly sophisticated transformations make it possible to produce textile fibres similar to polyester or to be used in the manufacture of tyres as a replacement for smoky black.