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Cultivation of wheat arised thousands of years ago with both durum and emmer wheat being discovered in Egyptian tombs of the first dynasty. The discoveries of wheat in these tombs indicates that wheat cultivation along the Egyptian Nile river occurred at least 6,000 years ago. Chinese traditions suggest that the Chinese were growing wheat as far back as 2,700 BC. Wheat cultivation has occurred for the last 5,000-6,000 years around the Eastern Mediterranean and Mesopotamia with plenty of evidence that wheat was the principal and most important staple food for the ancient civilizations of Babylon, Egypt, Crete, Greece and Rome (Matz, 1991). The production and utilization of wheat has been linked with agricultural as well as civilization development over the last 12,000 years so it can be seen that wheat production has been occurring for many thousands of years. The exploitation of this wheat has been a global phenomenon and has facilitated community settlement, religious and cultural development and continuos population growth because food has been produced in sufficient quantities to support these things. Additionally wheat is able to tolerate a range of conditions for growth which does not restrict its production to particular regions making it a highly valued product all over the world (Gooding & Davies, 1997).
Various different species of wheat was cultivated to feed the population within the Mediterranean region further illustrating the importance of wheat many centuries ago. The dominance of wheat in the Roman Empire was immense leading to the area often being referred to as a wheat empire, however the great migration from the north led to displacement of wheat by rye for a certain duration. Rye was a more important food within Europe during the middle ages in comparison to the different types of wheat available at that time but proportion of wheat to the total grain utilised for food was significantly larger than indicated by the production with the simple reason behind this being because rye had uses as feed whereas wheat was predominantly used for food purposes.
Wheat had eventually risen to be known as the finest of the cereal foods and its availability for food purposes was believed to indicate a high stage of civilization. The significance of bread within the western world became increasingly greater as wheat quality improved, thus leading to higher quality bread production. The versatility of wheat is such that it is harvested all year round all over the world such that in any given month wheat will be harvested in a number of countries depending on climate for example in January it is harvested in Australia, New Zealand, Argentina and Chile and in March in India and northern Egypt (Pomeranz, 1988).
Wheat is the name specified to species that come under the Triticum genus, with this genus being classified under the Triticeae Dumort tribe which also happens to contain rye(Secala)Â and barley (Hordeum) genera. Within the Triticum genus, cultivated species tend to be grouped depending on the amount of chromosomes they have; 14(diploid), 28(tetraploid) or 42(hexaploid). Hexaploid wheat represents the most common wheat used for human consumption (wheat: more than just a plant journal). As it is the one consumed the most by humans, hexaploid wheat is the most cultivated and important of the different varieties of wheat as it is extremely versatile in that it can be grown under many climactic conditions and different soils (modern cereal chemistry kent-jones). with the varieties being grouped based on a number of different factors; milling properties (hard or soft), the rheology of the dough (strong or weak), colour of the bran (red or white) and vernalization requirements (spring or winter) (Florian DiekMann: commodity of the quarter wheatâ€¦journal). Within each of these factors, further classification of wheat goes according to bushel or test weight(measure of bulk density), grain cleanliness(avoiding contamination with other cereal grains, weed seeds and any foreign material) and moisture content amongst other factors(wheat chemistry and technology Pomeranz).
Within wheat and the products derived from wheat exist many essential nutrients for the human diet. Wheat is a great source of all the following; energy, fiber, carbohydrates, proteins, B vitamins, iron, calcium, phosphorus, zinc, potassium and magnesium further illustrating why wheat is a staple food all over the world, in particular in Africa and asia where wheat along with other cereals contributes over 70% of energy in the populations diet (Y Pomeranz (ed 1) Wheat chemistry and technology page 11-12).
The wheat grain
The wheat grain consists of three main components; the bran, the germ and the endosperm each responsible for different functionalities. The bran is used primarily for feed, the germ is used as a food supplement for diets and the endosperm is utilized to produce flour (Y Pomeranz (ed1) page 15). Endosperm constitutes approximately 82% of the wheat kernel and is made up primarily of a proteinaceous matrix within which granules of starch are embedded, the bran constitutes approximately 15.5% and is made up of all the outer layers including the aleurone layer, which is removed during the milling process along with the other layers, but botanically is actually the endosperms outer layer. Finally the germ makes up 2.5% of the wheat kernel and consists of both the scutellum and the embryo (Fate of starch in food processing: Jan A. Delcour page 88, effect of wheat pearling on flour quality severino pandiella).
PANDIELLA, EFFECT OF WHEAT PEARLING
Spikelets forming two vertical rows with one row either side of the central stem (also known as rachis) are what make up a single ear of wheat. Several florets create a single spikelet with each floret being an individual flower which, as with all grasses, has an ovary consisting of an ovule (a single egg cell). This ovule eventually develops into a seed post-fertilisation which stays enclosed inside the wall of the ovary. Upon ripening of the structure, the ovary wall begins to form the pericarp, the thin outer layer made up of fibrous tissue with the seed still strongly attached. The seed possesses a seed coat known as the testa and this along with the pericarp on the outside is the general form of the wheat grain (cereal science and technology).
The wheat grain possesses two very distinctive sides; the ventral side which is dissected by a crease, and the dorsal side which is the curved back of the grain. Opposite to the germ end (where the embryo is encapsulated) is the brush end, covered in a fine layer of thin hairs. The bulges present on the sides of the crease located on the ventral region are known as the cheeks with the dorsal regions adjacent to the region of the embryo known as the shoulders of the grain (wheat production and utilization page 22)
Botanically, the wheat grain is classified as a fruit as it has a seed inside a pericarp and in particular does not open up and release the seed making it an indehiscent fruit. This type of fruit is generally called a caryopsis by botanists however the wheat grain tends to be called a seed, grain, berry or kernel. Grain seems to be the most appropriate reference for the wheat caryopsis as seed is incorrect, berries are succulent fruits with many seeds and kernel refers to the soft, edible interior of a nut.
As mentioned previously, the wheat grain comprises of three main parts being the bran, endosperm and the germ. In the early stages of the grain development, both the germ and endosperm are enclosed within layers of tissue until expansion of the endosperm occurs as a result of it becoming filled with starch. The consumption of starch by the endosperm results in the destruction of the tissue leaving the thin testa and the outer pericarp behind. The endosperm during its earliest stages consists of nuclei which freely segregate until the formation of cell walls occurs between them, the cells then progressively begin to divide, leading to the accumulation of starch, and then cell division stops. The formation of the aleurone layer occurs upon differentiation of the thick cell walls produced by the endosperms outermost layer and signals the end of the increases in surface area experienced by the endosperm(cereal science and technology). Wheat grains tend to be between 4-10 mm in length however the length of grains are usually affected by location of grain development on the spike and spikelet, as well as the variety of wheat that the grain belongs to (wheat chemistry and technology..hlynka isadore, page 56 joule library!)
The Starchy Endosperm
The starchy endosperm is responsible for producing commercial white bread flour while mill bran is made up of the wheat grains outer parts including the aleurone layer. Although the aleurone composition is significantly different to that of the endosperm, it is still a part of the endosperm thus giving rise to the term 'starchy endosperm' to distinguish them from each other. The germ and the aleurone represent the only living tissues within the wheat grain and both contain significantly large amounts of enzymes, different proteins, vitamins and lipids to the starchy endosperm, pericarp and testa (cereal science and technology). The proteins and enzymes within the aleurone layer play a pivotal part in the germination process (http://www.springerlink.com/content/ll783t36172031r6/fulltext.pdf and cereal science and technology)
Within the starch endosperm, starch granules of varying diameter ranging between 1-40Âµ (wheat starch and gluten, Knight, page 2) are fixed within a protein matrix, of which these proteins form the gluten (the storage protein of wheat(principles of cereal science and technology:carl hoseney page 8) within the process of dough synthesis (http://www.springerlink.com/content/ll783t36172031r6/fulltext.pdf(http://www.springerlink.com/content/ll783t36172031r6/)). Three types of cells; prismatic, central and peripheral, compose the starchy endosperm and each varying in shape, size and location within the grain (the storage protein of wheat(principles of cereal science and technology:carl hoseney page 8).
The characteristics of hard and soft wheat are believed to be brought about by the manner in which adherence occurs between the protein matrix and the starch granules. Within hard wheat, the starch granules remain fixed inside the protein matrix upon breakage, which tends to occur between the endosperm cells. Soft wheat on the other hand, stimulates the release of the starch granules from the protein matrix upon undergoing cleavage through the cells (cereal science and technology: palmer page 374). These characteristics are important with regards to the quality of the wheat grain as well as the end use of the milled flour from the grain.
The germ consists of the scutellum and embryo as previously stated. During germination, the new plant is formed by the embryo axis, the scutellum, located between the embryonic axis and endosperm, initially acts as an instant food reserve source prior to becoming the absorptive organ that governs food reserve translocation from endosperm to embryo axis. The embryo is the most fundamental part of the grain responsible for ensuring the survival of the species due to its capabilities of forming plants of the filial generation. Lipid and lipid-soluble vitamins are present in the highest concentration within the embryo compared to anywhere else in the grain, along with the highest moisture content (cereal grain structure and development, tony evers, cereal science and technology).
The bran is comprised of all the outer layers of the grain (effect of wheat pearling;severino pandiella) being the testa, pericarp and including the aleurone layer, all of which greatly differ in their compositions. The testa contains non-starch carbohydrates, cutin-like material and phenolic pigment (cereal science and technology page 378), the pericarp is predominantly made up of non-starch carbohydrates from a cell wall origin and the aleurone, as mentioned earlier, consists of significant amounts of proteins, lipids, minerals, vitamins and enzymes within the contents of the cell and pentosan within the thick cell walls (cereal science and technology).
Chemical composition of wheat grain
**** come back to this *******
Starch is a carbohydrate that is in abundant supply all over the world, existing within green plants as semi-crystalline, microscopic granules with diameters ranging from 0.5-175Âµm (starch hydrolysis products: worldwide technology and applications, characteristics of pores in native and hydrolyzed starch granules pages 23-25).
Pure isolated starch is a white, amorphous and tasteless solid without any odour and is also insoluble in cold water (the starch industry, jw knight page 1). Starch has been widely and diversely used in many different branches of industry as a raw material, most commonly upon modification using enzymatic as well as chemical and physical methods (characteristics of pores in native and hydrolyzed starch granules). Starch's versatile nature is because of its molecular structure which, in relation to temperature and water, has been reported to provide unique properties like solubility, viscosity,gelling and adhesion. Hydrolysis of starch to simpler molecules like glucose is also relatively easy and allows for a wider range of derivatives to be produced. (wheat production and utilization page 285)
Starch is made up primarily of two polymers of glucose; lineal amylose (20-25%) and branched amylopectin(75-80%)(Enzymatic hydrolysis of Wheat starch into glucose journal, Ewa Nebesny, Justyna ROSICKA) (see figure), both arising as a results of the linkages of a substantial amount of glucose molecules, linked end to end within amylose polymer, and branched within amylopectin polymers (wheat production and utilization page 285). The general formula for these polymers is (C6H10O5)x(STARCH chemistry and technology, 2nd ed, Roy Whistler, James BeMiller, page 154).
Common starches are around 20-25% Amylose(the starch industry, knight, page 21) and consist of Î±-(1,4)- linked D-glucopyranosyl units with a low amount of branching and less than 1% linkages, making it almost linear. The molecular weight of amylase falls within the range of 105 - 106(Fate of starch in food processing: From raw materials to final food products). Even in dilute solutions of 1% or less, amylase stability is such that it is highly unstable in water. While around 20-25% Amylose is present within common starches, the granules can range from 0-85%, leading to the starches having significantly differing properties; for example dissolution in starches with 50% or more amylose content can only occur at temperatures above 95oC. Post gelatinization (to be discussed later), stiff gels are formed rapidly upon cooling. Precipitation as a floc readily occurs within dilute solutions and at higher concentrations a rigid surface film is created by the gels. Precipitated amylose as well as high amylose starches can only undergo redispersion if exposed to significantly higher temperatures of around 120oC(starch hydrolysis products: page 26-28).
Amylopectin (around 75-80% in common starches), in contrast to amylose is highly branched and is like amylose is made up of chains of Î±-(1,4)- linked D-glucopyranosyl units joined together through Î±-(1,6) linkages. It has a molecular weight of 107-108, known to be significantly high for naturally occurring polymers (Fate of starch in food processing: From raw materials to final food products). In contrast to amylose, amylopectin is relatively stable in water solutions and with exception of significantly high concentrations, amylopectin gels possess soft and fluid properties. At temperatures of around 50oC, reversibility of amylopectin gels that exhibit rigidity occurs. Crystallization of amylopectin within concentrated gels â‰¥30% occurs in two ways; upon leaving to stand or if dried to a film.
Generally, amylose presence determines gelation properties of starch whilst amylopectin presences determines the starch granule structure and swelling properties (starch hydrolysis products: page 28). Reactions of both amylose and amylopectin with iodine generate characteristic blue and red colours respectively, with the blue coming as a result of the strong adsorptive properties of amylose (the starch industry, jw knight, page 26-29).
Figure above taken from http://www.sigmaaldrich.com/etc/medialib/life-science/biochemicals/migrationbiochemicals1/Starch_GOP_Assay_Kit.Par.0001.Image.575.gif
Gelatinization of starch
The heating of starch in a sufficient amount of water leads to absorption of water and results in the swelling of the starch granules. It is possible to reverse this effect under a characteristic temperature known as the gelatinization temperature, however, at or above the gelatinization temperature irreversible modifications occur, resulting in starch granule disruption and crystallinity loss, this is known as gelatinization (Fate of starch in Food processing: From raw materials â€¦Jan A Delcour, Charlotte Bruneel). Gelatinization occurs as a result of the hydrogen bonds between poly-(1-4)-Î±-glucan chains breaking within the crystallites upon exposure to heating in the presence of water (as mentioned above). However, it can also occur at room temperature upon exposure to solvents such as liquid ammonia and dimethyl sulphoxide, and by mechanical means through milling(starch:properties and potential, BLANSHARD, page 33) (to be discussed later)
The gelatinization temperatures of starch vary greatly for different sources of starch. Tableâ€¦..illustrates the range of temperatures for different sources of starch, where the gelatinization temperature is likely to fall between.
Gelatinization temperature range(oC)
Wheat Starch A
Wheat Starch B
Cassava Starch A
Cassava Starch B
Potato Starch A
Potato Starch B
Maize Starch A
Maize Starch B
Reference = The starch industry, JW Knight, page 2
Enzymatic hydrolysis of starch
Starch is the most abundant carbohydrate component in wheat and wheat flour, giving rise to the term starchy endosperm, where it is exists as granules inside a protein matrix
Within flour, the total proteins can be divided approximately into two different fractions being soluble and insoluble fractions. The soluble fractions are obtained through extraction of flour or using water to manipulate dough. The insoluble fraction is what is known as gluten. Within the extraction process from flour (to be discussed later), the impure gluten is isolated and has the following characteristics; it is a consistent, rubber-like wet mass of a cream colour that has significant extensible properties. Vital gluten finds extensive use as a pivotal ingredient in yeast-raised baked foods, especially bread. Upon exposure to heat, destruction of gluten 'vitality' occurs. The gluten that is extracted from flour and utilised in its wet form exhibits all desired properties as it exists within the flour but upon this exposure to heat and drying treatment, the ability of the gluten to produce higher quality bread suffers. So the ideal form of gluten is of it's freshly extracted, hydrated and non-exposed to drying form(Wheat starch and glutenâ€¦KNIGHT PAGE 84-90).
Wheat milling process
***talk about hard and soft wheats?*****
Milling is the industrial process by which the starchy endosperm is separated from all the other grain components (cereal grain structure and development TONY EVERS AND S MILLAR PAGE 268). It is a process of producing flour using a number of stages with the two principle aims of; breaking the endosperm down into smaller, finer particles and removing the bran (effect of wheat pearling PANDIELLA). The generation of flour from whole wheat by the process of dry-milling and refining is the starting point from which the separation of wheat starch and protein(gluten) oocurs(laboratory scale dry/wet milling process for PETER STEENEKEN) . Upon milling into flour, the cells within the endosperm divide and begin to form endosperm agglomerates as well as free starch granules, and both proteicaneous matrix and starch are broken (Wheat starch and glutenâ€¦KNIGHT PAGE 2)
Modern methods of milling involve a complex set of processes consisting of grinding, separating and mixing which results in a wide range of different flour grades. Within common methods, the grooved cylinders that rotate at differential speeds are used to assist in the breaking of the grain leading to production of some fine flour refererred to as first break flour, coarse nodules of flour known as semolina and large fragments of grain which still have the layers of bran attached to them. Sieving seperates these three fraction after which they are fed successive break rolls in order to separate an increased amount of semolina from the bran. Seperation of the bran fractions may be done by sieving along with other processes such as air purifiers and further flour may undergo scraping from the bran by use of specialized equipment known as 'scratch' rolls. Semolina is further ground down to fine flour by a series of 'reduction rolls' with various different grain material streams being produced with each level of grinding. The amount that each different stream produces can be varied in order to produce flour of differing grades. These grain materials have varying compositions and particle sizes, leading to final flour commonly being a product of a significant amount of streams with 72% of grain being used in typical production of white flour. The remaining 28% of white flour tends to consist of milling by-products namely bran~(14%), middlings(12.6%), shorts(0.3%) and red dog(1.1%) (wheat production and utilization page 12-13).
As mentioned already, milling aims to remove the endosperm from all other grain components, in practive however, the removal of the starchy endosperm in a pure enough state for use as white baking flour is not entirely possible. A number of factors contribute to the amount of flour that is extracted like condition and natural weight per weight bushel, variety of wheat and its milling characteristics, preparation methods as well as the milling plant and techniques available and used (Modern Cereal Chemistry KENT JONES page 4). Post-extraction of flour leaves the wheat residue commonly known as wheat-feed, this is subsequently manufactured into feed for livestock.
Receiving and storage of wheat:
Wheat can be received via road, rail or water or by a combination of 2 or even all 3 of them. It is then stored in the elevator which consists of a number of different things; unloading facilities, scales, storage bins, conveying systems, wheat cleaning machinery and the associated equipment like exhaust systems, dryers, wheat turning and blending machinery. The wheat flows through the elevator and undergoes weighing, sampling and analysis for any foreign material or contaminants such as other seeds, straw, earth, sand, stones, insects, damaged kernels for example burnt or immature kernels and so on, moisture and protein content of wheat also undergoes analysis.
The wheat is weighed and then coarse foreign material is removed upon sieving the wheat through a grate, it is then passed over a magnet and through an initial cleaner known as a receiving separator on route to a storage bin which classifies and stores the wheat according to class, grade and protein content. The receiving separator goes about removing materials that are considerable larger or smaller than wheat kernels for example sticks, stones and other coarse and fine materials by utilizing inclined oscillating sieves and reciprocating screens. Additionally, exhaust systems (also called aspirators) that can be built into the receiving separator or exist as a separate unit, filter out lighter impurities such as wheat chaff, shrivelled kernels and dust.
*********scan image of receiving separator from Pomeranz*****************
The cleaned wheat is transported via a conveyor to the main storage bins which tend to be hopper-bottomed with single or multiple bin outlets. Wheat is then transferred to intermediate storage bins via a conveying system, different grades may be blended from this wheat to produce a milling grist that satisfies requirements. This movement of dry wheat always results in generation of dust within the elevator and this must be removed to prevent contamination of wheat. This is achieved by use of a central exhaust system possessing suction inlets capable or removing dust generated in open conveyors as well as preserving a negative pressure in closed conveying systems, bins and machinery.
Preperation of Wheat for milling:
Extensive cleaning of wheat, as already implied, is imperative and the precleaning machine alone is not enough concerning the removal of foreign or hazardous materials like stones, mud, straw, ergot and other seeds which can detrimentally affect appearance or functionality of the milled product and can possible even lead to damage of the mill. So prior to milling, wheat transfer from the elevator to the cleaning section (known as the 'screen room' occurs. Here the wheat is tempered (conditioned) with an appropriate amount of water in preparation for milling(Y pomeranz).
The first step in the cleaning process involves wheat passing through a separator fairly similar to the receiving separator in the elevator section but designed to be more selective in the removal of larger or smaller impurities than wheat. As wheat is passed through the separator, the top screen removes all larger impurities like corn and soybeans and the finer sieve of the bottom screen filters the smaller impurities like mustard, flax and rapeseed as well as sand which are all collected separately. The wheat, now semi-cleaned, goes over the finer sieve and into the aspirator, where the lighter impurities of shrivelled kernels, chaff and dust are removed by currents of air (Y Pomeranz wheat chemistry and technology volume 2 page 8). The wheat is then passed to a destoner that makes use of specific gravity separation to remove stones (cereal science and technology page 392) which works by propelling denser stones upwards towards the head of an oscillating and inclined metal screen while wheat moves down the screen to the outlet (Y pomeranz). Shape separation is carried out by disc or cylinder seperators which remove barley and oat grains from the wheat while continuos use of aspirators occurs for reasons mentioned previously (cereal science and technology). The use magnetic seperators occurs at various locations primarily at the wheat intake point at the start of the cleaning section and prior to high-speed frictional cleaning machines and the first break rolls, these are utilized to remove any ferrous materials in the wheat such as iron or steel (Y pomeranz). Finally, prior to tempering, scourers are used to clean the wheat by removal of dirt and other impurities like beeswing (modern cereal chemistry PAGE 180) from the grain's surface and from the ventral crease (cereal science and technology) before the addition of water to the wheat's surface.
Post cleaning is the tempering (or conditioning stage) of the wheat before it enters the milling stage. Here moisture is added to the wheat under controlled conditions in order to;
Increase the skin's durability such that it defies powdering when milling occurs as it is not possible to separate powdered bran from flour at all in the milling process
Facilitate separation of endosperm from the bran
Soften the endosperm to allow for easy reduction to flour
Ensure that materials coming out from the grinding rolls are in optimum condition to ease the sifting process
Ensure grinding generates the optimum level of damaged starch in correspondence with the wheat hardness and flour's end use
Tempering of the wheat is pivotal in ensuring milling can be carried out with maximum efficiency and optimum performance is achieved in the end product (Y Pomeranz).
A controlled amount of water is added to the wheat to increase the moisture content so it is at its optimum for the milling, the wheat is then left to stand in a tempering bin for a certain period of time to allow for the water to distribute throughout the wheat and diffuse into each wheat grain thus being capable of reaching an optimum moisture distribution throughout. Wheat that is too dry leads to friable bran that be crushed easily rendering it significantly difficult to separate from the millstreams, on the other hand wheat with too high moisture content can result in the process becoming slower due to flour being difficult to sieve out so tempering is vital with the amount of water added depending upon the original moisture content and type of wheat(cereal science and technology). Soft wheat grains are usually tempered to achieve around a 16% moisture content while hard wheat grains brought to around 17.5% moisture content with duration of tempering being 4-6 hours and 10-36hours(Y POMERANZ)respectively (milling of wheat journalâ€¦reference within is of Hoseney (1986))
The conditioning of different wheat grades occurs in seperate tempering bins and subsequently blended together in correct amounts to achieve a mixture called a grist. From this grist, flour of a desired quality can be milled. Finally before being sent to be milled, magnetic seperators remove any ferrous materials and then wheat is passed through a scourer to remove bran (beeswing) along with dirt and dust in the crease.
Milling of wheat into flour:
As mentioned previously, milling is a process of grinding which is performed by break rolls, sizing rolls and reduction rolls, and separating by use of sifters and purifiers. The main objective is to shatter the wheat grain in order to extract as much of the endosperm from the bran skin as physically possible in correspondence with getting flour that satisfies the ash or color specification requirements. Then this endosperm has to be reduced into flour by grinding it down.
*** a simplified flow diagram of the milling process is shown below***.
(extracting starch from grain)
Within the refinery, the starch slurry that arrives from the wheat department is processed and gives rise to the production of glucose. There are three different channels that run within the refinery and each produce different grades of glucose as a result of using starch treatments specific to each particular channels.
Cargill's requirements on the refinery are for the starch to be broken down into glucose of varying grades in line with the requirements of their customers. The starch that arrives into the refinery can be used to produce these different grades of glucose upon conversion by use of enzymes. After this there are more processes to refine the glucose even further so that it reaches an acceptable standard for the customers.
On the refinery the creation of 9 base grades of glucose occurs, determination of which occurs from each grade's individual sugar profile. Further blending of these 9 grades can facilitate the production of more than a 100 other grades of glucose.
This breakdown of starch into glucose is known as Saccharification. Liquefaction is the process by which saccharification occurs and these different grades of glucose are produced. As mentioned previously, a molecule of starch is comprised of a large number of Dextrose molecules joined in a long chain. Employment of acids and enzymes can result in the reduction in size of these starch molecules and result in starch paste being made thin enough to be able to handle. As there are different types of starch molecules, different enzymes must be used to facilitate this process of Liquefaction.
In channel 1, starch undergoes acid hydrolysis by use of hydrochloric acid which is added to the starch, along with hydrolyzing the starch it reduces the pH of it to 2. Reducing the pH to 2 is of particular importance further down the process as it enables the desired Dextrose Equivalent (DE) value to be obtained. This is then heated by use of steam, to around 150oC to allow conversion to occur, a DE of between 50-60 is obtained at this temperature. The temperature is then reduced to 60oC within the flash cooler and ODE is produced and stored within the converter tanks.
There are three products in total that are ever produced on channel 1 however only one of these products is produced on any given day. The three products are; ODE, REX and RGL which are different base grades of syrup. ODE is the most common product produced on channel 1, REX is produced 1-2 times a week and RGL production is rare. The converter tanks from which samples were taken are always filled with ODE as standard and if REX was to be produced, gluco-amylase and beta-amylase enzymes are added to the converters to allow conversion of ODE into REX.
Use of a Side Arm Heater (SAH); a shell and tube heat exchanger, is utilized for the purpose of preparing the starch from attack by the enzymes within the converters. Here the raw preheated starch undergoes blending with a low viscosity starch, of a high temperature that re-circulates through the reactor and SAH. This process is vital in prevention of raw starch being backed onto the SAH tubes.
Heat is injected to the starch by use of a sophisticated heat transfer device known as a Hydro Heater causing a rapid increase in temperature, resulting in the swelling of starch molecules and subsequent destruction of starch bonds and thus exposure of starch bonds to attack by enzymes.
A different ion exchange technique is utilized on channel three and is called the ISEP. Here, there are 11 ports on the anion and the cation, liquor flows through these ports and the resin inside the cells removes all the charged impurities. The exhausted resin is regenerated using the remaining ports.
The following processes as can be seen in figures â€¦â€¦. Describe parts of the process that occur on all three channels.
All three channels facilitate the breakdown of starch by utilizing enzymes, which act as the catalysts of the starch conversion. Residence times are allocated to the starch-enzyme mixtures at particular and ideal temperatures, to allow for the conversion to occur.
The pre-coat filters, also known as the rotary vacuum filters are used by all three channels. Their role is to separate and remove all proteins and fats from the converted liquor. The temperature of the pre-coat filters is maintained at around 60oC. The rotary drum is submerged within a tank of the liquor and within the rotating drum is a vacuum, this stimulates the movement of liquor through the filter cake from the bay. The remaining fat and protein molecules are left on the protein bed, these are then cut off and used as animal feed by-products.
Further removal of impurities and unwanted material like fats and proteins is facilitated by the use of carbon. Reactivation of carbon occurs upon passing through a furnace, from which the heat destroys all the adsorbents and impurities. When carbon can finally no longer adsorb material that comes through the furnace then it is known to be "spent"
Prove-up or leaf filters, are designed to filter the liquor, removing any unwanted substances and carbon fines by using a differential pressure mechanism. A high differential pressure however indicates exhaustion of the prove-up system and a replacement filter bed on the leaf will be required.
Resin Columns (Channel 1 & 2)
The resin columns are responsible for impurity removal and facilitate this by removing both anions and cations (ion exchange). There are 3 pairs of resin columns each possessing both a cation and an anion exchanger however only 2 pairs are in use whilst the 3rd pair are regenerated. The used pairs are regenerated by being flushed with HCL and NaOH to remove any impurities that are bound to the resins.
Wiegand Evaporators or falling film evaporators as they are sometimes referred to as, distribute the product through heat exchangers to undergo evaporation upon heating by steam. This heat energy that is added facilitates the evaporation of water and thus leading to an increase in dry solids content of the liquor.
Ground Storage and Blending
The 9 base grades of glucose produced in channels 1,2 and 3 are then distributed to the ground storage and blending sections where they can be blended to produce different grades of glucose for use by different customers.
Base grade products
Tableâ€¦illustrates the different base grade products produced in the refinery on all 3 channels. The dextrose equivalent range is shown for each glucose unitâ€¦DP1 (GLUCOSE), DP2(MALTOSE), DP3(MALTO-TRIOSE), DP4*****
************include table here of products*******