Biscuits PDF

BISCUITS What is Biscuit? One of the difficulties in writing about biscuits is that the very word means different things to different people. In America the word ‘biscuit’ is used to describe a chemically leavened bread type product the nearest equivalent of which in the UK might be a scone. The pr...

BISCUITS What is Biscuit? One of the difficulties in writing about biscuits is that the very word means different things to different people. In America the word ‘biscuit’ is used to describe a chemically leavened bread type product the nearest equivalent of which in the UK might be a scone. The products known as ‘biscuits’ in the UK are called ‘cookies and crackers’ in the USA. Though there are so many meanings of word ‘biscuit’ we can defined the word ‘Biscuit’ as A small leavened, baked, crispy, flat & sweet product. Ingredients of Biscuits: Major Ingredients: 1. Wheat Flour 2. Sugar 3. Shortening Agent (Fats/Oils) 4. Water (RO water) 1. Leavening Agent (Physical, Chemical & Bio-logical) 5. Invert Syrup Minor Ingredients: 2. Common Salt (NaCL) 3. Ammonium Bi-carbonate – (NH4)2CO3 4. Acidulants 5. Emulsifier (Lecithin, Finamul) 6. Sodium meta bi-sulphite (SMBS) – Na2S2O3 7. Skimmed milk powder (SMP) 8. Anti-oxide (optional) 9. Flavors 10. Colors (optional) 11. Enzymes (as per requirement) Functions/Importance of Ingredients: 1. Wheat flour: It is most important basic ingredient in biscuit making without which no biscuits can be made. The main function of flour in biscuit making are a. Form the structure of biscuits b. Retain the gas during fermentation & baking c. To form dough during mixing, holding all the ingredients uniformly distributed in the dough and making it possible for easy machineability Wheat flour is the only ingredient with significant amounts of gluten forming potential. It also contains starch which gelatinizes (absorbs water) and stabilizes the structure. Two proteins found in wheat flour, glutenin and gliadin, form an elastic substance known as gluten when stirred with water. There are as many as 30 different types of protein in wheat, but only these two have gluten forming potential. When wheat flour is moistened and  manipulated through stirring, beating and kneading and/or handling, these two proteins grab water and connect and cross-connect to form elastic strands of gluten. If flour has a lot of these proteins, it grabs up water faster, making strong and springy gluten. The magical and elastic gluten network that forms serves many functions in a recipe. Like a net, gluten traps and hold air bubbles. They later expand from the gas from the leavening when a recipe is baked, causing the dough or batter to rise. During baking, the stretched flour proteins (gluten) become rigid as the moisture evaporates from the heat of the oven and sets the baked goods structure. The visco-elastic properties of gluten provide the perfect combination of elasticity and rigidity by expanding with the gas while still holding its shape. No other grain has been able to replace this function of wheat in baking. 2. Sugar: Beyond its contributions as a sweetener and flavor-enhancer, sugar have the following importance in biscuit preparation. a. Interacts with molecules of protein or starch during baking & cooking process. This process gives rise surface coloration during baking process. During baking the reducing sugars combine with amino acids from protein. This is known as Maillard reactions. This reaction gives attractive foxy brown color on the surface of biscuits. The higher the concentration of the reducing sugars, darker will be the color. The Maillard reaction is more prevailing in alkaline than in acid concentration and this is one of the reasons why sodium bi-carbonate is used in biscuits recipe to increase the alkalinity. Maillard Reaction: It is a chemical reaction between amino acids and reducing sugars that gives browned food and its distinctive flavour. The reaction is a form of non-enzymatic browning which typically proceeds rapidly from around 140 to 165 °C (280 to 330 °F). The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavours. This process is accelerated in an alkaline It is named after French chemist Louis-Camille Maillard, who first described it in 1912. 1. The carbonyl group of the sugar reacts with the amino group of the amino acid, producing N- substituted glycosylamine and water 2. The unstable glycosylamine undergoes Amadori rearrangement, forming ketosamines 3. Several ways are known for the ketosamines to react further: a. Produce two water molecules and reductones b. Diacetyl, pyruvaldehyde, and other short-chain hydrolytic fission products can be formed. c. Produce brown nitrogenous polymers and melanoidins The open-chain Amadori products undergo further dehydration and deamination to produce dicarbonyls. This is a crucial intermediate. Dicarbonyls react with amines to produce Strecker aldehydes through Strecker degradation.Acrylamide, a possible human carcinogen, can be generated as a byproduct of Maillard reaction between reducing sugars and amino acids, specially asparagine, both of which are present in most food products. b. Acts as a tenderizer by absorbing water and inhibiting flour gluten development, as well as delaying starch gelatinization. During the mixing process, sugar acts as a tenderizing agentby absorbing water and slowing gluten development. During the mixing of dough’s flour proteins are hydrated (surrounded with water) forming gluten strands. The gluten forms thousands of small, balloon like pockets that trap the gases produced during leavening. These gluten strands are highly elastic and allow the dough to stretch under expansion of gases. However, if too much gluten develops, the dough becomes rigid and tough. Sugar competes with these gluten-forming proteins for water and prevents full hydration of the proteins during mixing. Consequently, less gluten is allowed to ‘develop’ preventing the elastic dough from becoming rigid. With the correct proportion of sugar in the recipe, the gluten maintains optimum elasticity, which allows for gases to be held within the dough matrix. These gases, from leavening agents and mixing, expand and allow the dough to rise. c. Incorporates air into shortening in the creaming process. Sugar crystals become interspersed among shortening molecules when shortening and sugar are creamed together. Sugar helps to promote lightness by incorporating air into the shortening. Air is trapped on the face of sugar’s irregular crystals. When sugar is mixed with shortening, this air becomes incorporated as very small air cells. During baking, these air cells expands when filled with carbon di-oxide and other gases from leavening agent. d. Caramelizes under heat, to provide biscuits with pleasing color and aroma.Sugar caramelizes when heated above its melting point, adding flavor and leading to surface browning which improves moisture retention in baked products.At about 1750C, melted dry sugar takes on an amber color and develops an appealing flavor & aroma. This amorphous substance resulting from the breakdown of sugar is known as caramel. In  baking dough containing sugar, caramelization takes place under the influence of oven heat, and is one of two ways in which surface browning occurs. Caramelization Reaction: Caramelization or sugar browning occurs when any of different types of sugars are heated over their melting point. When heated by dry heat granulated sugar will melt at around 1600C and with continue heating melted sugar will gradually turn brown to form caramelized sugar. Extreme heat pulls the water out of the sugar molecule to form furfural derivatives that undergoes a series of reactions that are polymerized to brown coloured compounds. So, it is the browning of sugar used extensively in baking, cooking for the resulting sweet nutty flavour and brown colour. The brown colour is produced by three groups of polymers named as Caramelans(C12H18O9), Caramelens(C36H50O25), and caramelins(C125H188O80). As the process occurs volatile chemicals such as diacetyl are released producing the characteristic caramel flavour.Like the Maillard reaction, caramelization is a type of non-enzymatic browning. The process is temperature-dependent. The rate of caramelization is generally lowest at near- neutral acidity (pH around 7), and accelerated under both acidic (especially pH below 3) and basic (especially pH above 9) conditions. e. Speeds the growth of yeast by providing nourishment. As a fermentation food, in fermented dough, addition of small quantities of sugar encourages the yeast to grow more vigorously and hence speed the fermentation process. 3. Shortening agent (Fats/Oils): Fats and oils ae used in dough as surface sprays, cream filling and coating. The important functions of shortening are as follows… a. It imparts shorting effect to the dough and hence the biscuit is soft textured b. It makes the dough more extensible and the machining property of the dough is improved c. It improves the palatability of biscuits 4. Water (RO water): Water plays an important role in biscuit making. It is added in the dough stage and driven out in the baking stage. Between the time of its addition and removal it has a number of functions. a. It hydrates the flour particles & helps in the formation of dough suitable for further processing. b. It helps to dissolve the salt, chemical, sugar, water soluble color and flavor and to distribute the dissolved materials throughout the dough. c. It helps in the aeration of biscuits to certain extent by formation of steam. 5. Leavening Agents (Physical, Chemical & Biological): a. Physical Leavening agent: Air is incorporated through sifting, beating, mixing, molding and creaming. That air comes out during baking process in oven and helps to puff. Water vapor or steam has some minimal leavening effect and contributes to the improvement of texture and volume of dough. b. Chemical leavening agent [Sodium bi-carbonate (NaHCO3)]:Sodium bi-carbonate (Baking Soda) is the only salt generally used. in combination with equivalent amount of acidulants or as alone leavening agent. It liberates carbon di-oxide and aerates the product. It also neutralizes acidity contributed by invert syrup. An excess of baking soda results in a biscuit with alkaline PH and give rise to yellowish crumb, surface coloration and unpleasant soapy taste. 2NaHCO3 Heat Na2CO3 + H2O + CO2 Heat Fat + NaOH/KOH Glycerol + Sodium/potassium salt of fatty acid (Soap) c. Bio-logical Leavening agent (Yeast): In certain fermented verities , yeast is used as one of the ingredients. Yeast is a single cell living organism. It utilizes fermentable sugars in the dough and liberates mainly carbon di-oxide and alcohol. Maltose/Sucrose/starch Glucose & Fructose Yeast Yeast CO2 + Ethyl alcohol Yeast generally used in biscuit industry is Saccharomaces cerevesiae. Its quality & quantity have direct bearing on fermentation. T contains several enzymes which can convert sucrose, maltose and starch into simple sugar glucose & Fructose. Glucose & Fructose are further metabolized into carbon di-oxide and water in presence of oxygen but in absence of oxygen they produce carbon di-oxide and alcohol. In case of sponge fermentation of wheat flour by yeast, the oxygen availability is limited and hence carbon di-oxide & alcohol are formed. The presence of bacteria in the flour and in the compressed yeast used also will utilize the sugar to produce organic acid. On baking all this contribute to the flavor development and aeration in the product. Active dry yeast or fresh compressed yeast can be used. 6. Invert sugar syrup: The disaccharide sucrose is split up into a 1:1 mixture of the monosaccharide’s fructose and glucose.This split up is occurs by acid hydrolysis of sucrose. one molecule of sucrose consuming one molecule of water. As a consequence, the density of the solution increases with progressing degree of inversion, and the volume decreases. Sucrose Sucrose solutions rotate the plane of polarized light. The angle at which the plane of polarized light is rotated is specific for each sugar and depends on its concentration. An aqueous solution of saccharose is dextrorotatory. It causes a specific rotation of +66.5°. The specific rotation of glucose is +52.5°, but fructose is strongly levorotatory (-92°). While inverting, the specific rotation gradually undergoes a change in direction of polarized light from +66.5° to -19.7°. The inverted solution is levorotatory and displays a specific rotation of -19.7°. That’s why it is called as inverted sugar syrup. Procedure of Preparation of Invert Syrup: a. Pour the required quantity of water in a steam jacketed (electrically heated) stainless steel kettle and start heating b. When water temperature reaches at 600C gradually add required quantity of sugar passing through rare earth magnet (to arrest iron present in sugar) into kettle by automation or manually. During addition of sugar stirrer of the kettle should be running otherwise charring of sugar may happen and which may cause black particles in invert syrup.  c. Add required quantity of citric acid (dissolving in measured water) when temperature of solution in kettle reaches at 1020C. d. Heating should be continuing with constant stirring until temperature reaches at 112 – 1150C. e. Stirring should be continue for 20 minutes after discontinuing heating at 1150C. f. Check the Brix of syrup and ensure that it is 78±2 degree (otherwise further heating may require to evaporate excess water) g. Transfer the syrup to cooling tank (having cooling jacket arrangement) and cooled it at room temperature as early as possible. h. The PH of syrup should be of 2.7 – 3.5 and the color should be pale yellow and taste should be like honey. In biscuit preparation or bakery industry inverted sugar syrup have so many acts as follows. a. It acts as a tenderizer by absorbing water & inhibiting flour gluten development, as well as delaying starch gelatinization. b. Take part in Maillard reaction to provide biscuits with pleasing color & aroma c. Controls the formation of sugar crystals d. It helps to retain the moisture in product e. It acts as flavor enhancer and also as preservative. 7. Common Salt (NaCL): Salt is usedin almost all recipes for its flavor enhancing properties. Salt also toughens the gluten and hence reduces stickiness. Particle size of salt is important particularly when used for sprinkling on surface of biscuit. 8. Ammonium bi-carbonate [(NH4)2CO3]: Ammonium bi-carbonate is being used extensively in biscuit making. During baking it completely decomposes into ammonia, carbon di-oxide and water vapor and no residual salt is left out. It has an excellent aerating property. It is readily soluble in water and is very alkaline giving softer dough which requires less water for a given consistency. Despite the strong smell of ammonia only a small proportion of the available gas is lost when it is dissolved in water and held at normal temperature. Even in solution for 24 hours, little of its potency is lost. The dissociation is rapid at 600C, i.e. well into the oven as the dough pieces are baked. Being a carbonate, it reacts with other acidic ingredients, but the alkalinity conferred on the dough is not carried through the baked biscuits. 9. Acidulants:Commonly used acidic ingredients are not true acids but are acidic in nature. At room temperature they are not usually soluble in water but at elevated temperature they dissolved in water present in dough and react with baking soda to liberate carbon di-oxide. These gas bubbles form the nucleation sites for further expansion as the gas is heated and the vapor pressure of water rises during baking. It is therefore important that bubbles are  formed in huge quantities and very tiny size to produce a fine & even texture in the baked biscuits. some examples of acidulants, Mono Calcium Ortho Phosphate Mono hydrate, Potassium bi-tartrate, Sodium Acid Pyro Phosphate(SAPP), Dicalcium Phosphate dihydrate (DCP), Glucono Delta Lactone (GDL), Adipic Acid. NaHCO3 + RH (Acidulant) water Na-R + H2O + CO2 Emulsifiers: Certain emulsifiers are Lecithin, Glycerol mono stearate (GMS), Finamul etc. Emulsifiers or surfactants are chemical product which alters the surface properties of other materials with which they come in contact. They orient themselves along the interface or boundary of two adjacent surfaces. All emulsifiers are surface active agent which can promote emulsification of oil & water phases because both hydrophilic and lipophilic group within the same molecule. An emulsifier consists of water-soluble hydrophilic part (polar) and water insoluble, oil-soluble lipophilic part(non-polar) within its. When an emulsifier is added to a mixture of water & oil, the emulsifier is arranged on the interface, anchoring its hydrophilic part into water & its lipophilic part into oil. Thus, it reduces the surface tension at the interface substances by complexing with both. That is the force to separate the oil and water is thus weakened, resulting in the easily mixing of oil & water.So, the main function of emulsifiers in biscuit production are a. Stabilize oil in water or water in oil emulsion b. Modifies the fat crystallization c. Changing the dough consistency, stickiness and starch gelling aspects by complexing starch/protein. d. Lubricating low fat dough. 10. Sodium meta bi-sulphite (SMBS): Sodium meta bi-sulphite is a reducing agent normally used to modify the rheological property of dough. The addition of 50 – 100 ppm brings about dramatic changes in dough quality. Sulphites break the disulphide bond of gluten and hence weaken it.Hence dough contains SMBS lacks elasticity. SMBS is mostly used in semi-sweet hard dough to reduce mixing time and energy required for mixing. Use of SMBS also enables to reduce the final temperature. The addition of SMBS reduces the water requirement and hence the baking time. Na2S2O5 + H2O 2Na++ 2H- + 2SO32- Na2S2O3 2Na++ SO32- SO32- is the active ions which react with flour protein. The action of Sulphites of glutenin, which gives cohesive and elastic properties to gluten, is to break some of the sulphide bridges between protein molecules, thus weakening the cohesive and elastic structure. 11. Skimmed milk powder (SMP): When fat is separated from milk for cream or butter manufacture, a white fluid, rich in lactose and proteins remains. This is known as skimmed milk and when it is dried then it is called as Skimmed Milk Powder. In biscuit production there are so many positive effects on biscuit as bellow… a. Increase the absorptive quality of the dough, acts as strengthening agent to floor proteins & promotes the dough strength. b. Improves the mixing tolerance of dough c. Contributes to the golden-brown crust color of biscuit because of it lactose, caseinogen and wheat protein contents d. Promotes the larger fermentation which reduces the dough acidity e. Improves nutrition, flavor & eating quality of biscuits. 12. Anti-oxidants: The anti-oxidants prevent the development of rancidity in biscuit during storage. Some of the permitted ant-oxidants are Ethyl Gallate, Propyl gallate, Octyl gallate, Butylated Hydroxyanisol (BHA), Citric acid, Tertiary butyl hydroxy quinone (TBHQ). 13. Flavors: Biscuits and other bakery products may be flavored by including the flavor in the dough by dusting or spraying the flavor after baking and by adding in the cream. The flavourants can be natural spices or synthetic aromatic chemicals. Since biscuits are baked at higher temperature and also has low moisture, loss of flavor or change in the flavor characteristics are expected. Some of the flavors that are most satisfactory in biscuit industry are like vanilla, butter flavor, cheese, almond, chocolate etc. 14. Colors: Colors are generally not used in biscuit shell. However, they are used in creams required for cream biscuits. some permitted colors which are used in biscuit industry are for RED – Ponceau, Carmoisine, Erythrosine; for YELLOW – Tartrazine yellow, Sunset yellow; for BLUE – Indigo Carmine, Brilliant Blue FCF; for GREEN – Fast Green FCF. 15. Enzymes: Enzymes are catalyst. Normally enzymes are not used in sweet and semi-sweet biscuits, but occasionally used in cracker dough. The enzyme used in cracker dough is protease. This protease enzyme breakdown the gluten & hence softens the dough and improves the sheet-ability. Proteolytic enzymes are used in cracker dough partly to modify the consistency of the dough and tenderize the eating quality of product. These enzymes breakdown the structure of glutenin by catalyzing the hydrolysis of peptide linkages in the molecule. Process Flow Chart of Biscuit Production IngredientsWeighed Chemical Solution Preparation Mixing of sugar, fat, invert syrup, flavor, SMP and chemical solution separately in a creamer (cream preparation) for 7 – 12 minutes Mixing of prepared cream and Wheat flour in a mixer in addition with SMBS for 6 – 15 minutes (depending variety) – Dough Prepared Prepared Dough is Fed into Dough Hopper Rotary (Moulder/Cutter) Baking Oven for 5 – 15 minutes depending on variety of biscuit Cooling in Cooling tower and time should be approx. 3 times of baking time Packaging Storage  MAJOR MACHINERIES REQUIRED FOR BISCUIT PRODUCTION AND THEIR FUNCTIONS 1. Mixer: The majority of batch mixer used for preparation of biscuit doughs fall into one of two main categories, Vertical Spindle Mixer & Horizontal Drum Mixer. a. Vertical Spindle Mixer: The basic principle of construction are illustrated in given diagram The ingredients for a batch of dough are measured into a wheeled dough trough (a) which is moved into position and locked into the mixer base (b). The mixing paddles are carried on the lower ends of two or three shafts (c) which can be lowered and raised into and out of the dough trough by a carrier bar (d) driven by a small electric motor (e). The upper part of the shafts is splined and (at about 20 rpm) by the main motor (f) through a gear train housed in the fixed cross beam (g). the whole mechanism is supported by the two side pillars (h). This type of mixer has been used to mix all types of biscuit dough but mixing times for hard sweet doughs tends to be excessively long (up to 90 minutes per batch).  b. Horizontal Drum Mixers: The basic principles of construction of this type of mixer are illustrated in bellow diagram. The ingredients are mixed in a U-shaped bowl (a) shown in dashed outline. This bowl is locked in an upright position during loading and mixing can be rotated about a horizontal axis to enable the dough to be discharged at the end of the cycle either into a dough trough for transport to the dough forming machine, or, in many cases, directly into a hopper which feeds the dough forming machine located on the floor below the mixing room. Unlike the troughs of spindle mixer, the mixing bowl of the horizontal mixers is frequently fitted with a water jacket either at the flat ends of the bowl or over the larger curved surface. Mixing is carried out by paddle blades (b) which are driven about a horizontal axis (c). The mixing bowl and paddles are supported between two enclosed station (d) which also contain the dive motors & gear trains for the mixing rotor and the tub-tilting mechanism. Ingredients are metered into the mixing bowl through openings and pipework (e) in the entablature (f) above the bowl. The speed of the mixing paddles in different mixers varies considerably. The speed of paddles are in the region 35 rpm. In some mixer two paddles run in different speeds like one is in 30 rpm another one is at 70 rpm. The higher speeds of paddles are particularly useful in mixing hard dough which require a large energy input. 2. Rotary for Shaping (moulding/wire-cutting) of Biscuit: Short doughs are normally formed into the required final shape for baking by a process known as ‘Rotary Moulding’. In this process (Fig – A) the dough is compressed by a grooved roller (a) into biscuit-shaped engravings on a parallel moulding roll (b). Surplus dough is continuously cut from the surface of the moulding roll by a sharp knife (c) and return to the feed hopper via grooved roller.  The dough pieces are removed from the engravings on the moulding roll by means of a canvas web, previously impregnated with fat, which is pressed against the moulding roll by a third rubber-covered roll (d). Soft doughs are also processed into the required final shapes for baking by an extrusion process. The two most common procedures are the wire-cut process (Fig-B) and the bar or rout-press process (Fig-C). In both types of equipment, the dough is forced by two contra rotating grooved rollers (a) through a group of dies above a transfer web or directly into the oven band. In the wire-cut equipment the extruded dough is cut at the die face by an oscillating wire (e) into roughly circular discs. In the bar-press a series of continuous parallel ribbon of dough are extruded which may or may not have a pattern of grooves in their upper surface. The ribbons are cut into rectangular bar shapes by means of a guillotine (f) either before or after baking. 3. Laminator for Sheeting, Laminating & Cutting: The most complex machinery for forming biscuit dough pieces is that required for the manufacture of hard dough biscuits. One arrangement of equipment for making this product is shown diagrammatically in bellow Fig. Two fairly thick (20 – 25 mm) sheets of dough (a and b) are produced continuously by two groups of three rollers known as sheeters. A thin layer of a fat -flour mixture (c) [ Flour 100%, Fat 27% and salt 1.5%] is spread over the upper surface of the lower sheet and the second sheet of dough is laid over this filling. This filling is required for cracker biscuit but not for other hard dough biscuit. This filling is sometimes known as ‘Powder’ or ‘Cracker Dust’. The thickness of this dough sandwich is progressively reduced by passage through pairs of heavy reduction rolls (d), usually three in number, the gap between each successive pair of rolls becoming progressively narrower. The thin dough sandwich is then built up into a thicker dough sheet (e), consisting of 4-6 layers of the sandwich, by laying the dough backward and forward across another much slower moving at right angles to the direction of the initial sheet. The thick pile of dough sheets is ag ain progressively reduced in thickness by passage through a further set of reduction rolls (f) to obtain the desired final thickness of the sheet which is of the order of 1.5 mm. The final pair of reduction rolls, which are used to make small adjustments to the thickness of the final dough sheet, are usually referred as ‘Gauge Rolls’. To minimize shrinkage of the dough pieces after cutting, the tension in the final dough sheet is reduced by transferring the sheet onto a further conveyor, moving in the same direction but a slightly slower speed. Under some operating conditions this transfer produces a small ripple or wave in the dough sheet, causing the slower moving conveyor to be known as a ‘waving band’/‘Relaxing web’ (g). Dough pieces of the required size by means of a reciprocating head carrying appropriate dies, or more commonly by a rotary cutter (h). A rotary cutter consists of two synchronized cylinders, the first of which impresses the pattern of docker holes and lettering onto the dough sheet. The second cylinder cuts the outline shape of the biscuit, thus freeing the dough piece from the dough sheet. Cutting scrap from between the dough pieces is continuously removed (k) and recycled to an earlier stage in the process. The cut dough pieces are then deposited on the oven band. 4. Baking Ovens: The majority of commercially made biscuits are now baked in heated tunnels on continuous conveyors which form the baking surface. These tunnel ovens vary in length from about 30 meters to about 150 meters. The oven bands are commonly 1.0 – 1.2meter-wide though some ovens have bands up to 1.5 wide. The principal features of construction of a biscuit oven are shown diagrammatically The oven band (a) carrying the product to be baked passes through an insulated, heated tunnel which is constructed of a number of sections. Each section is individually heated & controlled. In the diagram three sections (b), (c) and (d) are shown; in practice the number of sections maybe as high as ten or more depending upon the length of oven. After baking is complete the product is transferred to a cooling conveyor (not shown in diagram) and the oven band passes round a driven drum (e) and returns underneath the oven to a tensioning drum (f) at the feed end of the oven. The band return may be open and at ambient temperature, in which case the band losses much of the heat gained during baking process. So, an additional heat may be imparted by an appropriate heater on the band return (g) Ovens are commonly heated by combustion of gas, although oil fired or electrical heating is used where gas is not readily available or is too expensive relative to the cost of other fuels. The ovens in which the gas burned inside the baking chamber are known as ‘direct fired ovens. In the other types of oven, the gas (or oil) is burned outside the baking chamber and the heat is transferred to the product being baked by a variety of methods. Such ovens are known as ‘Indirectly fired oven’. The humidity of the atmosphere in directly fired ovens is higher than that in indirectly fired ovens by reason of the moisture in the products of combustion. As a rough approximation one third of the humidity present in the atmosphere of a directly fired oven is derived from the products of combustion. The products of combustion (where present) and the moisture and other volatile products of the baking process are extracted from the oven sections through exhaust ducts [in diagram  (h), (k) and (l)]. Each duct is fitted with a damper to control the rate of extraction. Ideally extraction of waste gas from each oven section should be exactly balanced by an input of fresh heated air into the section. By this means sideways transfer of atmosphere from one section to another is prevented. Types of Ovens: a. Multi-burner Ovens: This type of oven is the direct descendent of the traditional beehive oven mentioned above and is currently the type most commonly used in the biscuit industry. In this ovens ribbon, or strip, burners are placed across the width of the oven at frequent intervals along the length of each section both above and below the band. The baking chamber itself is constructed of fire brick mounted in an iron framework or alternatively made of cast iron heavily insulated to retain the heat. b. Indirectly Fired Radiant Ovens: These ovens have a single burner for each section. The hot gases from this burner pass along pipes (about 2 inches in diameter) running parallel to the length of the oven above and below the band before being vented through exhaust ducts. Construction of baking chamber is otherwise similar to that of a multi-burner oven. c. Forced Convection Ovens: In these ovens air is heated by a single burner for each section and the hot air blown by a fan through carefully designed ducts to slot or nozzles arranged in rows across the width of the baking chamber above & below the band. The velocity of the hot air impinging on the product can be controlled by means of dampers located in the supply ducts. After contact with the product the air is recirculated through the burner/heat exchanger, an appropriate proportion being vented through the exhaust ducts. Forced convection ovens and their air supply ducts are constructed from steel sheet. The outer casing of the baking chamber is insulated to conserve heat. d. Hybrid Ovens: Hybrid ovens aim to combine features of both radiantand forced convection ovens, but rarely achieve this objective in a satisfactory manner. Changes Occurring in the Biscuits During Baking in Oven During the baking in oven many changes takes place in the biscuit dough. The most important of these are changes in dimensions of biscuit, loss of moisture from biscuits and the development of color & flavor in biscuits. The total baking process in oven can be seen to fall into three phases. In the first phase expansion of the dough and the loss of moisture commence. In the second phase the expansion of dough & the rate of loss of moisture both reach their maxima. In this second phase the development of biscuit color commences, particularly on any high spots on the dough surface. In the last phase most biscuits become thinner, the rate of loss moisture decreases and the intensity of color of the product surface continues to increase. Dimension Changes:The increase in volume of dough during baking cause by the action of aerating agents and by steam produced from the dough moisture. With fermented doughs carbon di-oxide produced by yeast plays an important role. Yeast is rapidly killed at a temperature of 550C or above. So with a total baking time of only 2 – 4 minutes the time available for carbon di-oxide production will be very short. However this mechanism appears to be important, possibly by initiating the separation of the laminations in the cracker dough which are then further expanded by steam. The majority of biscuit products are of course chemically aerated. The most commonly used reagents are sodium bicarbonate alone or with acidulant, and ammonium bicarbonate. The thickness of biscuit depends not only upon the aerating agents present but also on the condition existing in the oven (Oven Profile – Temperature, Humidity and Positive Pressure). Change in Moisture Content: The initial moisture content of biscuit doughs ranges from about 11 – 30 % (Sample Basis). The final moisture content of freshly baked biscuit is usually within the range 1 – 5 % depending upon type of biscuit. In the above fig. it is shown that a short period of comparatively slow weight loss as the dough temperature starts to rise and surface moisture begins to evaporate is followed by a longer period of more steady loss as the free moisture surface recedes below the surface of the developing biscuit structure and finally a slowing down of the rate of weight loss occurs as the moisture content approaches its final low level. It is the end of baking process. Development of Color & Flavor: Caramelization reaction and Maillard reaction (between reducing sugar and amino acid) are involved development of biscuit color & flavor during baking in oven. Color first appears on any raised part of biscuit surface and as baking continues the color spreads to the other part of biscuit surface. During baking volatile compounds are also formed which contribute to the aroma and flavor of freshly baked biscuits but some these compounds are lost during cooling & storage. Another factor contributing to the appearance and color of some biscuits is the humidity in the oven atmosphere at the early stage of baking. When baked in an oven with a dry atmosphere these biscuits have a dull surface appearance and a rather harsh color. If the oven conditions are adjusted so as to build up humidity in the first section the surface of finished biscuit develops an attractive sheen and its color is normal. The End Point of Baking: The completion of the baking process is in general judged by two properties of biscuit. Its color and its moisture content. Other properties such as eight, liner dimension and general appearance are of course of great importance but these properties are governed by conditions existing prior to the later stages of baking. The color of the biscuit controls to a considerable extent its initial acceptability by the consumer. The moisture content controls the stability during storage of the mechanical integrity of some biscuits and the development of stale flavor in most biscuits. Oven Profiles and Baking Times: Temperature Profile of most of the biscuit is shown above with maximum heat intake is at first and second zone and next zone completes the baking zone. Last zone helps in coloring of biscuit. As generalization the hottest temperature (300 – 3500 C) are used for cracker (fermented dough) products containing little or no added sugar. The semi-sweet and sugar containing biscuits are baked at somewhat lower temperature (about 250oC) and the short/soft dough biscuits are baked at about 200oC. The temperature profile of modern tunnel ovens may be regarded as having started with uniform conditions along with the oven length which have been modified by trial & error method to obtain satisfactory products each baked in a constant period of time (Baking Time). In general baking time of short/soft dough biscuit varies from 3.5- 7 minutes, for fermented dough and semi-sweet dough biscuit it is from 3.5 - 5.5 minutes. 5. Cooling Conveyor: Cooling is the one of the important part of biscuit production. As biscuits emerged from oven they are very hot and very soft. The biscuits have a temperature over 100 0C when they just come out of oven. They have to be gradually cooled to 45 – 480C before they are packed. The cooling time depends on ambient temperature but it should be at least 3 times of baking time. Improperly cooled biscuits affect the shelf life due to onset rancidity of or presence of high moisture content. 6. Biscuit Stacking Machine:At the end of cooling conveyors, there is a stacking machine. The function of this stacking machine is to collect biscuits from cooling conveyor, form them into lanes and stack them on the edge. The performance of the stacking machine may be improved if the spacing between rows is increased before the biscuits reach it. After proper  stacking of biscuit in stacking machine they are feed into packing machine by automation or manual process. 7. Open Wire Mesh / Continuous Steel Band: There are two types of oven band for production of biscuits, Wire Mesh Band & Continuous Steel Band Open Wire Mesh Band: These vary in construction from an open, rectangular mesh with four or five wires to the inch and weighing about 12 oz per square foot to closely woven thick meshes, sometimes known as ‘cord weave’, weighing 4.5 pound per square foot. Almost for all types of biscuits this band can be used except soft cooking with high fat content. One of the advantages of wire mesh bands is the ease of release or aerating gases and stream from the base of the products during baking. Continuous Steel Bands: These bands, of the order of 2 mm thick, are used to bake all soft biscuit doughs and some short and semi-sweet biscuit. They permit flow or spread of soft and short dough during baking. They also produce a thin bottom crust compared to the wire meshes, and thus contribute to a softer bite in the finished biscuits. on the other hand, they can contribute to problems with the release of steam and aerating gases from the base of the dough pieces during baking, producing uneven or hollow backs on the biscuit if baking conditions are not properly controlled.  Types of Biscuits and their Processing Biscuits are basically classified according to their dough characteristics or dough making procedure 1. Short dough or Soft Dough biscuits (any glucose biscuit, cookies): Contain more fat, less water and with lesser mixing time 2. Hard dough or Semi-sweet biscuit (Marie Biscuit):Contain less fat, more water and high mixing time 3. Fermented Dough biscuit (Cream Cracker biscuit): Fat, water and mixing time almost same as hard dough biscuit. In addition to that there is a fermentation step. PREPARATION OF SHORT / SOFT DOUGH BISCUITS Dry Creaming: Weighted quantity of Fat, Emulsifier, Sugar Powder, SMP, Invert Syrup and flavor should be taken in a creamer by manual or by automation. Switch on the stirrer of creamer with a speed of 80 – 100 rpm (varies depending of creamer machine). Preparation of Chemical Solution:Chemical solution should be prepared in a dosing tank. Weighted quantity of water to be taken in dosing tank and then add salt, sodium bi-carbonate and ammonium bi-carbonate sequentially and after each addition run the stirrer at least for 2 minutes to make proper chemical solution. Wet creaming:Now the prepared chemical solution poured into previous creamer and stir the stirrer for at least 3 minutes to make the cream batter. Mixing Process: Wheat flour is to be taken in mixer and then transfer the prepared cream batter into mixer and start mixing for required time 4 – 5 minutes (varies depending on quantity & quality of gluten present in flour). Over mixing or low mixing should be avoided for better quality of biscuit. During mixing cooling of dough or heating of dough may require which have to controlled by passing hot or cool water through jacket which is installed with mixer. During mixing solution of SMBS can be used as dough conditioner up to acceptable limited quantity. Standing before Dough Feeding: With batch mixed dough there is inevitably a time interval between the end of mixing and the start of processing by the dough-forming machine. During this time period changes in dough properties may occur. short or soft dough undergo changes in consistency during post mixing standing times. These changes have the appearance of the dough drying out but are more probably caused by the slow uptake of free water in the dough by the hydrophilic component present. It is frequently stated that this change slows or stops after about 30 minutes. This statement is used to justify the practice of allowing this type of dough to stand for 30 minutes or longer between mixing & machining. However, measurements of dough consistency on standing have shown that the increase in firmness of the dough continues almost linearly for a considerably longer period than 30 minutes and is associated with increase in firmness of dough pieces moulded from the dough and with decrease in stack height (thickness) of final product. If the rate of dough production is not accurately matched to the rate of usage by the forming machine the standing time will vary, thus contributing to the batch to batch variation in dough properties as well as biscuit properties. Dough Feeding: After proper standing time dough is to be fed onto the Rotary Moulder to get required shaped raw biscuit (Discussed earlier) Baking of Biscuit: After moulding the raw biscuits are transferred to wire mesh and entered into oven. The oven should be properly heated before entering raw biscuit into oven. As discussed already there are three zones in oven Proofing Zone which may also called as Heating Zone, then Baking Zone and lastly Coloring Zone. The wire mesh carries the raw biscuit through above zones of oven and baked biscuit properly. (what happens inside the oven is discussed earlier). Cooling of Biscuits: Cooling is the one of the important parts of biscuit production. As biscuits emerged from oven, they are very hot and very soft. The biscuits have a temperature over 1000C when they just come out of oven. They have to be gradually cooled to 45 – 480C before they are packed. The cooling time depends on ambient temperature but it should be at least 3 times of baking time. Improperly cooled biscuits affect the shelf life due to onset rancidity of or presence of high moisture content. Packing & Storing of Biscuit: After proper cooling and desired temperature of biscuits, they come into stacking machine and from which they are transfer to wrapper packing machine manually or by automation. The wrapped biscuits are then packed in polybag (if required) and then filled in cartoon Box and then stored suitable atmospheric condition.  PREPARATION OF HARD / SEMI-SWEET DOUGH BISCUITS Due to its high-water content and relatively low amount of fat and sugar, produces extensive gluten system and structure. The long mixing time develops the gluten and the mixer action stretches and orients the gluten strands to a point where much of elasticity is destroyed. What happens during Mixing: Due to mechanical action coupled with water addition to wheat flour and other ingredients results in dough film formation and thus final dough. All the starch granules will be surrounded by water manifolds and reaches the proteins. This result in gluten complex formation. This protein complex is a continuous; three dimensional networks of very fine threads and fibrils distributed through the dough mass and thus imparting elasticity and mouldability to the dough. The solution of sodium meta bi-sulphite (150 – 200 ppm SO2 on flour weight) is used during mixing which reacts with disulphide group of flour protein to break the disulphide links. This reaction ensures the shape of the biscuit as it cut. This developed dough mass is subjected to forming. Do not required any standing time for stress relaxation but if allowed to stand for any reason they too must be protected from the changes in temperature. But the hard dough not treated with SMBS must be allowed to stand for a period of 30 – 45 minutes in order to permit the stress set up in the dough during mixing process to relax. During this standing time the dough must be protected from changes in temperature, otherwise uneven temperature distribution within mass will contribute to variations in dough properties and as well as biscuit properties. (The process of Dry Creaming, Preparation of Chemical Solution, Wet creaming and mixing is same as soft dough biscuit except mixing time 6 – 7 minutes) Laminating, Sheeting & Cutting: The laminator reduces the dough to a thin sheet in successive stages and compacts into a laminated structure (As discussed earlier).The thickness of this dough is progressively reduced by passage through pairs of heavy reduction rolls, usually three in number, the gap between each successive pair of rolls becoming progressively narrower. The thin dough is then built up into a thicker dough sheet, consisting of 4-6 layers of the dough sheet, by laying the dough backward and forward across another much slower moving at right angles to the direction of the initial sheet. The thick pile of dough sheets is again progressively reduced in thickness by passage through a further set of reduction rolls to obtain the desired final thickness of the sheet which is of the order of 1.5 mm. The final pair of reduction rolls, which are used to make small adjustments to the thickness of the final dough sheet, are usually referred as ‘Gauge Rolls’. To minimize shrinkage of the dough pieces after cutting, the tension in the final dough sheet is reduced by transferring the sheet onto a further conveyor, moving in the same direction but a slightly slower speed. Under some operating conditions this transfer produces a small ripple or wave in the dough sheet, causing the slower moving conveyor to be known as a ‘waving band’/‘Relaxing web’. Dough pieces of the required size by means of a reciprocating head carrying appropriate dies, or more commonly by a rotary cutter. A rotary cutter consists of two synchronized cylinders, the first of which impresses the pattern of docker holes and lettering onto the dough sheet. The second cylinder cuts the outline shape of the biscuit, thus freeing the dough piece from the dough sheet. Cutting scrap from between the dough pieces is continuously removed and recycled to an earlier stage in the process. The cut dough pieces are then deposited on the oven band. Spray of Spray Solution: Condensed milk, Caramel and water are to be mixed as per desired proportionate ratio in a vertical batch stirrer. The spray mixer should pass through 60 meshes to separate any invisible particle, otherwise it will block the spray nozzle. Uniform spray of spray solution on biscuit has to be ensured through proper adjusting of the air & Spray solution flow. Baking of Biscuit: Baking time (3.5 – 5.5 minutes) should be as per standard for ensuring baking & better shelf life. All the other procedures are same as soft dough biscuits (discussed earlier) except bottom heat which is more compared to soft dough biscuit. Cooling of Biscuits, Packing & Storing of Biscuitare same as soft dough biscuits (discussed earlier). PREPARATION OF FERMENTED DOUGH BISCUITS Fermentation is carried out in two stages Slurry Fermentation and Sponge Fermentation. Fermentation room should have relative humidity of 78 ±2 % and temperature to be maintained 30 – 320C. For slurry fermentation time to be given is 2.5 to 3.0 hours depending upon the quantity of flour. Sponge fermentation is carried out for 36 – 48 hours depending upon the characteristic flavor development. For fermented dough biscuit flour should contain high gluten and also quality of gluten is expected to be satisfactory. Slurry Fermentation: 1. Weighted quantity of flour to be taken in fermentation trolley through automation or manually. 2. In homogenizer take weighted quantity of SMP, Yeast, grinded sugar, Papain enzyme 3. Required quantity of water to be added to the homogenizer and stirred it at high speed for at least 3 minutes. 4. The contents of homogenizer then to be poured to the fermentation trolley where already weighted quantity of flour has been taken. 5. The content of fermentation trolley to be mixed in vertical mixer for 5 minutes. 6. Now the prepared slurry is to be allowed for fermentation for 2.5 – 3.0 hours in fermentation room where temperature & humidity to be maintained as said earlier. 7. Check the slurry mass, it should not be sticky but fibril type structure. 8. There should be enough rise of 15 – 18 inch and fall of 3 – 4 inch of slurry in fermentation trolley. 9. Avoid over fermented slurry as indicated by high fall of slurry, it will not give the proper aroma and will create problem during cutting and sheeting. Sponge Fermentation: 1. Weighted quantity of ingredients Flour (65% of total flour in a batch), Water (40% total water in a batch) and yeast (2.4% of total yeast in a batch) and others as per recipe, taken in a dough trolley 2. Upper layer of previous sponge (if available) in small quantity can be added. 3. Now the content in dough trolley to be mixed in vertical mixer for 5 minutes. 4. The trolley then to be taken in fermentation room for 36 – 48 hours.  5. There should be proper development of aroma after the fermentation. Final Mixing: 1. The properly fermented slurry to be taken from fermentation room. 2. Butter, flavor, invert sugar syrup, sugar, prepared sponge to be added in it. 3. Rest quantity of flour weighted and to be added in it. 4. Previously prepared chemical solution (as discussed earlier for soft dough biscuit) to be added. 5. Total contents then to be taken in a vertical mixer and start mixing. 6. Within 2 minutes of start of mixing, required quantity of SMBS solution to be added on it and continue mixing for 10 – 14 minutes. 7. After dough preparation 30 – 40 minutes standing time to be given. Standing before Dough Feeding: With batch mixed dough there is inevitably a time interval between the end of mixing and the start of processing by the dough-forming machine. During this time period changes in dough properties may occur. Variation in standing time is of course also variation in fermentation time. The effect of such variation will depend upon the rate of microbiological activity in the dough but the tendency will be for the dough to become softer with increasing standing time. Laminator for Sheeting, Laminating & Cutting: The most complex machinery for forming biscuit dough pieces is that required for the manufacture of hard dough biscuits. One arrangement of equipment for making this product is shown diagrammatically in bellow Fig. Two fairly thick (20 – 25 mm) sheets of dough (a and b) are produced continuously by two groups of three rollers known as sheeters. A thin layer of a fat -flour mixture (c) [ Flour 100%, Fat 27% and salt 1.5%] is spread over the upper surface of the lower sheet and the second sheet of dough is laid over this filling. This filling is required for cracker biscuit but not for other hard dough biscuit. This filling is sometimes known as ‘Powder’ or ‘Cracker Dust’. The thickness of this dough sandwich is progressively reduced by passage through pairs of heavy reduction rolls (d), usually three in number, the gap between each successive pair of rolls becoming progressively narrower. The thin dough sandwich is then built up into a thicker dough sheet (e), consisting of 4-6 layers of the sandwich, by laying the dough backward and forward across another much slower moving at right angles to the direction of the initial sheet. The thick pile of dough sheets is ag ain progressively reduced in thickness by passage through a further set of reduction rolls (f) to obtain the desired final thickness of the sheet which is of the order of 1.5 mm. The final pair of reduction rolls, which are used to make small adjustments to the thickness of the final dough sheet, are usually referred as ‘Gauge Rolls’. To minimize shrinkage of the dough pieces after cutting, the tension in the final dough sheet is reduced by transferring the sheet onto a further conveyor, moving in the same direction but a slightly slower speed. Under some operating conditions this transfer produces a small ripple or wave in the dough sheet, causing the slower moving conveyor to be known as a ‘waving band’/‘Relaxing web’ (g). Dough pieces of the required size by means of a reciprocating head carrying appropriate dies, or more commonly by a rotary cutter (h). A rotary cutter consists of two synchronized cylinders, the first of which impresses the pattern of docker holes and lettering onto the dough sheet. The second cylinder cuts the outline shape of the biscuit, thus freeing the dough piece from the dough sheet. Cutting scrap from between the dough pieces is continuously removed (k) and recycled to an earlier stage in the process. The cut dough pieces are then deposited on the oven band. Baking of Biscuit: Baking time (3.5 – 5.5 minutes) should be as per standard for ensuring baking & better shelf life. At the initial zone bottom heat to be more than top heat to avoid crust formation. All the other procedures are same as soft dough biscuits (discussed earlier). Cooling of Biscuits, Packing & Storing of Biscuit are same as soft dough biscuits (discussed earlier) QUALITY CHECKING OF RAW MATERIALS In thebiscuit industry the Quality Inspection begins at the point of obtaining raw materials itself. The major ingredients like flour, sugar, fat, SMP etc. are checked on arrival at the Biscuit Manufacturing Plant. Materials Name Physical Analysis Chemical Analysis Flour Color, Dry Taste and smell, Moisture test, PH test, pecker’s test, Drinking taste, Gluten %, Alcoholic acidity % test, Total Ash test, Acid Insoluble test, water absorption power, Sedimentation value test, Protein test. Sugar Color, Crystal size, Turbidity and Moisture test, Sulpher di-oxide content, color in 50% solution Sucrose content. Fat Color, Odor and Taste FFA determination, Acid value test, Iodine value test, Per-oxide value test, Melting point test, Soap test, Adulteration test SMP Color, Taste & Flavor, Retention Moisture, Titrable acidity, Ash content, on sieve Bulk density, Protein & Adulteration test QUALITY CONTROL OR QUALITY ASSURANCE OF FINISHED BISCUITS Quality Assurance (QA): Quality assurance is process oriented and focuses on defect prevention. It is a set of activities for ensuring quality in the processes by which products are developed. It’s a proactive process and aims to prevent defects by concentrating on the process used to make the product. The goal of QA is to improve development and test processes so that defects don’t arise when the product’s being developed. QA can be achieved by establishing a good quality management system and assessing its adequacy. What’s more, everyone on the team involved in developing a product is responsible for quality assurance. Quality Control (QC): Quality control is product oriented and focuses on defect identification.It is a set of activities for ensuring quality in products by identifying defects in the actual products produced. It’s a reactive process and aims to identify (and correct) defects in finished products. QC can be achieved by identifying and eliminating sources of quality problems to ensure customer’s requirements are continually met. It involves the inspection aspect of quality management and is typically the responsibility of a specific team tasked with testing products for defects.