Food Science & Technology · Commodity Processing Technologies · also Bakery Technology, Baking Science, Bakery and Confectionery Technology
The science of bread, biscuits, cakes, pasta and snacks: ingredient functions, dough development, fermentation, baking, staling, and frying of snacks, with the defects and their causes.
In the exams: GATE XE-G Section 3 (bread, biscuits, extruded products, potato chips); ICAR AIEEA-PG Code 18 Unit III (cereals and bakery products)
Bakery, pasta and snack foods turn cereal flours, starches, fats, sugars and potatoes into some of the most widely eaten processed foods: bread, biscuits, cakes, pasta and noodles, chips and extruded snacks. The technology rests on a few physical and chemical events: the formation of a gluten network or a starch structure that holds gas or gives shape, the production and expansion of gas by yeast, chemical leaveners or steam, the setting of that structure by heat through starch gelatinisation and protein coagulation, browning reactions at the surface, and, in fried foods, the exchange of water for oil. Controlling these events is the difference between a light, even loaf and a dense one, a crisp biscuit and a hard one, firm pasta and sticky pasta, a chip with acceptable oil and colour and one without.
The subject matters industrially and nutritionally. Bakery and snack products are made at every scale, from village bakeries and namkeen makers to fully automated plants, and they carry large shares of the salt, sugar, fat and refined starch in modern diets, so reformulation to reduce them and to add whole grains and fibre is a constant task. Food safety issues, such as acrylamide formation in baked and fried foods, frying oil degradation and allergens, also cluster here.
The subject is examined in GATE XE-G Section 3, which names bread, biscuits, extruded products and potato chips, and in ICAR AIEEA-PG Code 18 Unit III (technology of cereals and bakery products). Examiners ask for the functions of ingredients, the steps and differences between bread-making processes, events during fermentation and baking, the causes of staling and of common defects, biscuit and cake types, pasta processing, snack manufacture and the factors in oil uptake, with short calculations in baker's percentages, dough temperature, baking loss, specific volume and oil content. Flour quality tests and milling are taught in cereal-science-milling, the chemistry of starch, proteins and frying oils in food-chemistry-major-constituents, acrylamide in food-toxicology-contaminants-allergens, and spoilage such as rope and mould in food-microbiology.
Bakery formulas are written in baker's percentages, in which each ingredient is expressed as a percentage of the flour weight, taken as 100. A dough with 1,000 g flour, 600 g water, 18 g salt and 20 g yeast is written as flour 100, water 60, salt 1.8 and yeast 2.0, which makes formulas easy to scale and compare.
Flour supplies the gluten-forming proteins and starch. Bread needs strong flour, commonly with about 11 to 13 per cent protein or more, whose gluten forms an extensible, elastic network that holds gas; biscuits and cakes use weaker, softer flours with lower protein. Starch absorbs water, gelatinises during baking and forms most of the crumb structure; damaged starch supplies sugars through amylase action. The flour quality tests that predict these behaviours are described in cereal-science-milling. Water hydrates proteins and starch, allows gluten formation and enzyme action, dissolves salt and sugar, and controls dough consistency and temperature; bread doughs typically use about 55 to 65 parts of water per 100 of flour, depending on flour absorption.
Yeast, Saccharomyces cerevisiae, ferments sugars to carbon dioxide, which leavens the dough, and ethanol, and contributes flavour. It is supplied as compressed (fresh) yeast with about 70 per cent moisture, which must be refrigerated, as active dry yeast that is rehydrated before use, and as instant dry yeast, which can be added directly to flour; dry yeasts are used at lower levels than fresh. Salt, usually about 1.5 to 2 per cent of flour weight, gives flavour, strengthens and tightens gluten, and controls yeast activity; doughs without salt ferment fast and are sticky and weak. Reducing salt in bread is a public health target in many countries and requires attention to dough handling and flavour.
Sugar is food for yeast in sweet doughs, though lean bread doughs ferment on sugars released from starch by amylase. It tenderises by competing with flour for water and delaying gluten development and starch gelatinisation, contributes to crust colour through Maillard reactions and caramelisation, adds sweetness, retains moisture and slows staling. In biscuits and cakes it is a structural ingredient, controlling spread and texture.
Fat, as shortening, butter, margarine or oil, lubricates the gluten network, allowing gas cells to expand smoothly and increasing loaf volume; it softens crumb, slows staling and improves keeping quality. In biscuits and pastries, solid fat coats flour particles and separates layers, giving shortness and flakiness; in cakes, creaming fat with sugar incorporates air. The solid fat content and crystal form of the fat at working temperature determine its performance, as explained in food-chemistry-major-constituents.
Improvers modify dough and bread properties. Oxidising agents strengthen gluten by promoting disulphide cross-links, improving gas retention and volume; ascorbic acid is the main one now used, converted in the dough to dehydroascorbic acid, which acts as the oxidant. Potassium bromate, once common, has been banned in many countries, including India in 2016, because it is a possible carcinogen. Reducing agents such as L-cysteine or sodium metabisulphite weaken gluten, used in biscuit and cracker doughs to reduce elasticity and shrinkage. Emulsifiers, such as diacetyl tartaric esters of mono- and diglycerides, sodium stearoyl lactylate and mono- and diglycerides, strengthen doughs and soften crumb. Enzymes include fungal α-amylase to supply sugars and soften crumb, xylanases to redistribute water from arabinoxylans, and maltogenic amylase to slow staling. Permitted improvers and levels differ between countries, so formulations must follow the relevant additive regulations.
In the straight dough method all ingredients are mixed together in one stage, and the dough then undergoes bulk fermentation, commonly one to three hours, with one or more knock-backs (punching) to expel gas, redistribute yeast and food and develop the gluten further. It is followed by dividing, rounding, intermediate proof, moulding, panning, final proof and baking. It is simple and suited to small bakeries but sensitive to timing: an over-fermented dough loses strength and gives sour, pale bread, while an under-fermented one gives low volume and poor flavour.
In the sponge-and-dough method, part of the flour (often about 60 to 70 per cent), with part of the water and the yeast, is mixed into a sponge and fermented for several hours, typically three to five. The sponge is then mixed with the rest of the flour, water, salt, sugar and other ingredients to form the dough, which needs only a short floor time before dividing. The long sponge fermentation develops flavour, conditions the gluten and makes the process tolerant of delays, which is why it has been widely used in large plant bakeries, particularly in North America. Pre-ferments such as poolish and biga in European baking and sourdough starters work on a similar principle. Sourdough uses a culture of lactic acid bacteria and yeasts; the bacteria acidify the dough, giving flavour, improving keeping quality and, in rye breads, controlling amylase activity and making the dough workable.
Mechanical dough development replaces most of the work of fermentation by intense mixing. The Chorleywood Bread Process, developed in the United Kingdom in 1961, mixes dough in high-speed mixers with a defined energy input, commonly about 11 watt-hours per kilogram of dough delivered within a few minutes, with an oxidising improver, extra water and yeast, and often with control of headspace pressure to adjust crumb structure. There is no bulk fermentation: the dough is divided immediately after mixing, so the total time from flour to bread is greatly shortened and lower-protein flours can be used. Most bread in the United Kingdom and many other countries is made this way. Critics argue that it gives less flavour than long fermentation, while supporters point to consistency and efficiency.
Continuous bread-making systems, developed in the United States in the 1950s, combine a liquid pre-ferment with continuous high-speed mixing and extrusion of dough directly into pans, giving a very fine, uniform crumb; they are now less common. Other variants include the no-time dough, in which strong oxidants and extra yeast shorten fermentation without mechanical development, and frozen dough and par-baked systems, in which dough or partly baked bread is frozen at a central plant and finished in retail outlets. Each process trades off flavour, time, cost, equipment and labour, and the choice depends on the market and scale of the bakery.
When flour and water are mixed, gluten proteins hydrate and, under mechanical work, unfold and align into a continuous viscoelastic network, while air is incorporated as small gas cells that become the nuclei of the crumb structure; yeast does not create new cells but expands those formed during mixing. Optimum development is shown by a smooth, extensible dough that can be stretched into a thin translucent film. Under-mixed dough is weak and gives low volume; over-mixed dough breaks down and becomes sticky.
Dough temperature controls yeast activity and fermentation time, so bakers set a desired dough temperature, commonly about 26 to 28 °C for bread. Mixing adds heat by friction. The water temperature needed is estimated by the classic rule: water temperature = (number of factors × desired dough temperature) − (sum of the other temperatures and the friction factor). For a straight dough, the factors are flour, room and water temperatures, so with a desired temperature of 27 °C, flour at 25 °C, room at 28 °C and a mixer friction factor of 10 °C, the water should be 3 × 27 − (25 + 28 + 10) = 18 °C. In hot climates, chilled water or ice is often needed.
During fermentation, yeast converts sugars to carbon dioxide and ethanol. The free sugars in flour are used first; then maltose produced from damaged starch by flour and added amylases sustains gas production. Carbon dioxide dissolves in the dough water until saturated, then diffuses into the gas cells and expands them. Two properties must match: gas production, which depends on yeast quantity and activity, sugar supply and temperature, and gas retention, which depends on the strength and extensibility of the gluten network. Fermentation also lowers dough pH, produces flavour compounds and organic acids, and changes dough rheology, making it more extensible.
After dividing, rounding and a short intermediate proof to relax the gluten, dough pieces are moulded into their final shape and placed in pans or on trays for the final proof, commonly at about 35 to 40 °C and high relative humidity, around 80 to 85 per cent, so that the surface does not skin. Proof continues until the dough reaches the required volume. Under-proofed dough gives tight crumb and splits in the oven; over-proofed dough collapses, giving coarse crumb and flat tops. Proof time and conditions are therefore controlled closely, and in large bakeries proofers are continuous, with pieces moving through on conveyors.
In the oven, heat reaches the product by radiation from oven surfaces, by convection from the hot air, which is increased by fans in convection ovens, and by conduction through the pan or band in contact with the dough. Inside the dough, heat moves mainly by conduction, helped by an evaporation-condensation mechanism in which water evaporates on the warmer side of gas cells and condenses on the cooler side. The crumb cannot rise much above the boiling point of water while it contains moisture, so the centre of a loaf reaches about 95 to 98 °C, while the surface dries and reaches much higher temperatures, forming the crust. Baking ends when the centre is fully set; a centre temperature of about 92 to 96 °C is commonly used as a guide. Baking times and oven temperatures depend on product size and type: small rolls bake quickly at high temperatures, large loaves more slowly.
The weight lost during baking, mainly water and a little ethanol and carbon dioxide, is the baking loss, usually around 10 to 12 per cent for pan bread: a dough piece of 560 g giving a loaf of 500 g has lost (560 − 500)/560 = 10.7 per cent. Oven types include deck ovens, rack ovens in which trolleys rotate in hot air, and continuous tunnel or travelling-tray ovens in large bakeries, with direct or indirect firing and zones of different temperature and humidity. Steam is injected at the start of baking for some breads to delay crust formation and give a glossy, crisp crust.
The events of baking follow the rising temperature. In the first minutes, the dough expands rapidly, a phenomenon called oven spring, because gases expand with heat, carbon dioxide becomes less soluble and leaves solution, ethanol and water vaporise into the gas cells, and yeast activity accelerates until the yeast is killed at around 55 to 60 °C. Enzymes are briefly very active, especially amylases, until they too are inactivated. Starch gelatinises, mostly between about 60 and 80 °C, absorbing water from the gluten; with the limited water in bread dough, gelatinisation is incomplete. Gluten proteins denature and coagulate from about 70 to 80 °C. Together these set the foam into a sponge: the gas cells, which were closed in the dough, rupture and become interconnected, giving the open crumb structure of bread.
At the surface, drying allows temperatures well above 100 °C, where Maillard reactions between reducing sugars and amino acids and caramelisation of sugars produce the brown colour and roasted flavour of the crust. These reactions also form acrylamide, as discussed in food-toxicology-contaminants-allergens; lighter baking reduces it. After baking, bread is cooled before slicing and packing, usually to a centre temperature of about 35 °C or lower, to avoid condensation in the package, which would encourage mould growth, and to allow the crumb to firm enough for slicing.
Staling is the set of changes after baking, other than microbial spoilage, that make bread less acceptable: the crumb becomes firm, crumbly and dry-tasting, the crust loses crispness and becomes leathery, and flavour fades. It is not simply drying out; bread stales even in a moisture-proof package. The main cause of crumb firming is retrogradation of amylopectin, in which the branched starch molecules gelatinised during baking slowly re-associate and recrystallise, stiffening the starch gel; amylose retrogrades quickly during cooling and contributes to the initial firmness of the crumb. The details of retrogradation are given in food-chemistry-major-constituents. Water also migrates from the starch to the gluten and from the crumb to the crust, which makes the crust soft and leathery and the crumb drier to the palate.
Temperature has a strong effect. Staling is fastest at refrigerator temperatures, around 0 to 5 °C, and slower at room temperature, which is why bread should not be refrigerated unless mould is a bigger problem than staling; freezing below about −18 °C almost stops it. Staling of crumb is partly reversible: reheating stale bread to above about 60 °C melts the amylopectin crystals and softens the crumb temporarily, which is why toasting or warming refreshes it.
Several strategies slow staling. Formulation helps: fat and sugar retain moisture and interfere with starch interactions; emulsifiers such as mono- and diglycerides form complexes with amylose that reduce starch re-association, softening crumb; and hydrocolloids hold water. Enzymes are widely used: maltogenic amylase hydrolyses the outer chains of amylopectin, shortening them so that they recrystallise less, which keeps crumb soft for longer without making it sticky, while excessive fungal or bacterial α-amylase can produce gummy crumb. Processing helps: adequate proof and full baking give well-set crumb, and rapid cooling followed by hygienic packing preserves freshness.
Storage choices matter as much. Room temperature storage in a closed package, or freezing for longer periods, is preferable to refrigeration. Shelf life of packaged bread is often limited by mould rather than staling; preservatives such as calcium propionate or vinegar, hygienic cooling and slicing, filtered air and modified atmosphere packaging control mould, while rope spoilage by Bacillus spores, described in food-microbiology, is controlled by acidity and propionate. A bakery's shelf-life claim must account for both staling and microbial spoilage.
Biscuits (cookies in American usage) are classified by dough type, which determines processing. Hard doughs, used for semi-sweet biscuits such as rich tea and Marie types and for crackers, have relatively low fat and sugar and more water, and their gluten is developed by mixing; they are elastic and tend to shrink, so they are sheeted, gauged through rolls and cut, often with reducing agents such as sodium metabisulphite or enzymes to relax the gluten, and are docked (pierced) to release steam and prevent blistering. Soft or short doughs, used for shortcakes, cookies and many sweet biscuits, have high fat and sugar and little water, so gluten development is minimal and the dough is crumbly rather than elastic; they are formed by rotary moulding, in which dough is pressed into engraved cavities on a roll, or by wire-cutting or depositing. Batters, with much water, are used for wafers, which are baked between hot plates, and for some drop cookies.
Crackers include cream crackers and soda crackers, made from fermented doughs that are laminated, folding layers of dough with fat or fat-flour mixtures to give a flaky structure; soda crackers traditionally undergo long fermentation of a sponge, which acidifies the dough before neutralisation with soda. Biscuits are baked in long continuous band ovens, typically tunnel ovens of many metres, with zones of different temperatures, followed by cooling, stacking and packing. Final moisture is low, often below 5 per cent, which gives crispness and long shelf life, but makes biscuits susceptible to moisture pick-up and fat oxidation, so packaging is chosen for low water vapour and oxygen transmission.
In cookies and soft biscuits, spread during baking is a key quality attribute. As the dough piece heats, fat melts and sugar dissolves, lowering viscosity so the dough flows outward until the structure sets as water evaporates and starch and proteins set. The spread ratio, width divided by thickness of baked cookies, is used to assess flours: a cookie 75 mm wide and 9 mm thick has a spread ratio of about 8.3. Soft wheat flours with low protein, low water absorption and low damaged starch give greater spread; hard flours and high damaged starch absorb more water, raise viscosity and reduce spread. Sugar particle size and amount, fat type and dough temperature also affect it.
Checking is the formation of fine cracks in biscuits hours or days after baking, causing breakage in packs. It is caused by moisture gradients: the centre of a biscuit leaves the oven moister than the edges, and as moisture equalises, the centre shrinks and the edges expand, creating stresses that crack the structure. It is controlled by more uniform baking, for example with radio-frequency or microwave post-baking dryers, and by formulation. Other quality measures include dimensions, weight, colour, moisture, texture by breaking strength, and sensory evaluation. Biscuits are one of the largest packaged food categories in India, where both hard and soft dough types are produced on high-speed lines.
Cakes are aerated, sweet, tender products made from batters rather than doughs. Their structure comes from egg proteins and starch rather than gluten, and their air comes from three sources: air incorporated during mixing, carbon dioxide from chemical leaveners, and steam during baking. Foam or sponge cakes, such as sponge and angel food cakes, rely on egg foam: whole eggs or whites are whipped with sugar to a stable foam, flour is folded in gently, and little or no fat is used. Shortened or butter cakes, such as pound cakes, rely on creaming: fat and sugar are beaten together so that sugar crystals cut air into the fat, creating cells that are later expanded by leavening gases and steam; eggs and flour are then added. Chiffon cakes combine oil with a meringue.
High-ratio cakes contain more sugar than flour, giving very moist, tender, sweet cakes with long shelf life. They require flours and fats that can carry the extra sugar and liquid: emulsified shortenings to hold the batter as a stable emulsion, and very fine, soft flours, which in some countries are treated with chlorine to modify starch and protein so that the cake sets without collapsing; chlorination of flour is not permitted in some jurisdictions, including the European Union, where alternatives such as heat-treated flour are used. Batter specific gravity, the weight of a fixed volume of batter divided by the weight of the same volume of water, measures aeration: a lower specific gravity indicates more air and usually higher cake volume.
Chemical leavening releases carbon dioxide from sodium bicarbonate. Bicarbonate alone gives off some gas when heated but leaves a soapy, alkaline taste and yellowish colour, so it is combined with acids in baking powders. Leavening acids, such as monocalcium phosphate, sodium aluminium phosphate, sodium acid pyrophosphate and glucono-delta-lactone, differ in how fast they react: some react mostly during mixing at room temperature, others mainly when heated. Double-acting baking powders combine fast and slow acids to release gas both in the batter and in the oven. The neutralising value of an acid is the parts of bicarbonate neutralised by 100 parts of the acid, used to balance formulations so that no excess alkali or acid remains.
Cake defects reveal faults. Collapse or a dipped centre comes from too much leavening, sugar or liquid, too little structure, under-baking or opening the oven too early. Tunnels, long holes in the crumb, come from over-mixing after flour addition, which develops gluten, or excessive leavening. A peaked or cracked top comes from too strong a flour, too hot an oven or too little leavening and liquid. Dense, heavy cakes result from under-creaming, too little leavening or batter that was left to stand, losing gas. Quality is assessed by volume, symmetry, crumb structure, tenderness, moisture and flavour.
Gluten-free products are needed by people with coeliac disease and some other conditions, and Codex defines gluten-free foods as containing no more than 20 mg/kg of gluten, as described in food-toxicology-contaminants-allergens. Without gluten, a dough cannot form an extensible, elastic network to hold gas, so gluten-free breads are made from batters rather than doughs, and structure must come from other ingredients. Base flours and starches include rice, maize, sorghum, millets, potato, tapioca and pseudocereals such as buckwheat, quinoa and amaranth. Hydrocolloids, especially hydroxypropyl methylcellulose, xanthan gum and psyllium husk, increase batter viscosity, stabilise gas cells and form films that partly mimic gluten. Proteins from egg, milk, soy or pulses and enzymes such as transglutaminase, which cross-links proteins, can add structure.
Gluten-free breads tend to have low volume, crumbly or gummy texture, rapid staling and lower nutritional value if based on refined starches, so formulations increasingly include whole-grain flours, fibre and protein. Production requires strict control to prevent cross-contact with wheat, barley and rye, through dedicated lines or validated cleaning, testing of raw materials and products by gluten-specific immunoassays, and controlled labelling, as discussed in food-safety-management-systems.
Whole-grain and high-fibre breads and biscuits are promoted for health because of their fibre, micronutrients and phytochemicals, but they present technical problems. Bran dilutes the gluten, and bran particles physically disrupt the gluten network and gas cell walls, so loaf volume is lower and crumb denser. Bran and fibre absorb much more water than flour, so doughs need more water and a longer mixing or hydration time. Whole-grain flours also contain more lipids and enzymes, giving shorter shelf life and stronger flavour, which some consumers dislike.
Bakers compensate in several ways: adding vital wheat gluten to strengthen the dough, using finer bran particles or pre-hydrating bran, using enzymes such as xylanases to modify arabinoxylans, adding emulsifiers and oxidants, and using sourdough fermentation, which improves volume, flavour and mineral availability by degrading phytate. Fibre-enriched products may also use isolated fibres such as oat and barley β-glucan, resistant starch, inulin and psyllium, which affect water absorption and texture differently and may support nutrition and health claims if conditions are met, as discussed in food-law-regulatory-affairs. Multigrain and millet-blended products, discussed in cereal-science-milling, are a growing category in India.
Pasta, in the Italian tradition, is made from durum wheat semolina and water, without fermentation or leavening. Durum semolina gives pasta its yellow colour, from carotenoid pigments, mainly lutein, and its firm cooked texture, from strong gluten and the hard endosperm. Italian law requires dried pasta to be made from durum wheat, while other countries permit common wheat or blends, often with lower cooking quality. Lipoxygenase in semolina can bleach the yellow pigments during processing, so low-lipoxygenase durum varieties are preferred.
In modern plants, semolina and water are mixed to about 30 to 32 per cent moisture, giving crumbly granules rather than a continuous dough, under vacuum to remove air, which would cause white spots and weaken the product. The mixture is kneaded and forced by a screw extruder through a die. Dies of bronze give a rough surface that holds sauce; dies with polytetrafluoroethylene inserts give a smooth, glossy, yellow surface. Long goods such as spaghetti are hung on rods, and short goods such as macaroni are cut at the die face. The pasta is then dried, the most critical step, from about 30 per cent to below about 12.5 per cent moisture, slowly enough to avoid cracking from moisture gradients. Traditional low-temperature drying took many hours; modern high-temperature and very-high-temperature drying, above about 60 to 85 °C, takes a few hours, coagulates the protein network more fully, improving firmness and reducing stickiness after cooking, and reduces microbial counts, but promotes Maillard reactions that redden colour and reduce lysine availability. Cooking quality is assessed by optimum cooking time, water absorption, cooking loss (solids lost to the cooking water), firmness and stickiness.
Asian noodles are usually made from common wheat flour rather than durum semolina, and are formed by sheeting and cutting rather than extrusion. Dough is mixed with salt or alkaline salts and relatively little water, rested, sheeted through a series of rolls to a thin sheet, and slit into strands. White salted noodles, such as Japanese udon, use salt and give soft, white noodles. Alkaline noodles, such as Chinese yellow noodles and ramen, use kansui, a mixture of sodium and potassium carbonates, which raises pH, gives a yellow colour from flavonoid pigments and a firm, elastic, chewy texture. Buckwheat noodles (soba), rice noodles, made from rice flour or starch by gelatinising and extruding or sheeting, and starch noodles from mung bean or other starches are other important types.
Instant noodles were invented in Japan in 1958 and are now produced in vast quantities worldwide, including in India. Noodle strands are waved, steamed to gelatinise the starch, cut into portions, moulded and then dried either by frying in oil at about 140 to 160 °C for a minute or two, which dehydrates them rapidly, creates a porous structure for quick rehydration and leaves an oil content commonly around 15 to 20 per cent, or by hot-air drying, which gives lower fat but slower rehydration. A seasoning sachet is added. Because fried instant noodles are high in fat and the seasonings high in sodium, reformulation and air-dried products are a focus, and frying oil quality must be controlled as described in chapter 11.
Potato chips (crisps in British usage) are thin slices of potato fried to low moisture. Quality depends heavily on the raw potatoes. High dry matter, measured as specific gravity, is wanted, commonly above about 1.08, because it gives higher chip yield and lower oil uptake. Low reducing sugar content is essential, because glucose and fructose react with asparagine in Maillard reactions during frying, giving dark colour, bitter taste and acrylamide. Potatoes stored at low temperatures accumulate reducing sugars, a process called cold-induced sweetening, so processing potatoes are stored at moderate temperatures, around 8 to 12 °C, with sprout suppressants, and potatoes that have accumulated sugars can be reconditioned by holding at about 15 to 20 °C for some weeks, which lets the sugars be respired or converted back to starch.
The process is washing, peeling, slicing to about 1 to 2 mm, washing slices to remove surface starch, blanching in some processes to remove sugars, removing surface water, frying in oil at about 160 to 190 °C until moisture falls to about 2 per cent or less, de-oiling, salting and seasoning, and packing, often under nitrogen to prevent oxidation and protect the chips from breakage. Finished chips usually contain about 30 to 40 per cent fat. Kettle chips are batch-fried in oil whose temperature falls when the potatoes are added, giving harder, crunchier chips. Fabricated chips are made from dehydrated potato doughs sheeted and cut to uniform shapes. Acrylamide mitigation, covered in food-toxicology-contaminants-allergens, is an important part of chip manufacture.
Extruded snacks are made by extrusion cooking of cereal flours, grits or starches, as described for breakfast cereals in cereal-science-milling. Direct-expanded snacks, such as corn curls and puffs, expand as they leave the die, are dried or fried and then coated with oil and seasoning. Third-generation or pellet snacks are made by cooking and forming a dough in an extruder under conditions that prevent expansion, drying the dense pellets to a stable moisture, and later expanding them by frying, hot air or microwave; pellets can be stored and shipped before expansion, allowing small finishing plants. Expansion of both types depends on moisture, temperature, shear, starch type and the levels of fibre, protein, sugar and fat.
Popcorn expands because each kernel's tough pericarp acts as a pressure vessel: when heated, water inside turns to steam until the pericarp ruptures at high pressure and the gelatinised endosperm expands into a foam. Kernels pop best at moisture around 13 to 14 per cent. Traditional snacks are enormously diverse. In India, namkeen such as bhujia, sev and mixtures are made by extruding or pressing gram flour and other doughs into hot oil, and include fried pulses, nuts and puffed or flaked cereals; papads are sun-dried thin discs fried or roasted before eating. These products are produced at every scale from household units to automated plants, and their quality depends on raw materials, frying oil management, moisture control and packaging against rancidity.
Deep-fat frying immerses food in oil at about 150 to 190 °C. Oil is an efficient heat transfer medium: heat flows by convection from the oil to the food surface, where the high heat transfer coefficient, increased by the turbulence of escaping steam bubbles, gives rapid heating. As the surface reaches the boiling point of water, water evaporates vigorously, and a drying front moves inwards. The outer zone dries, rises above 100 °C and forms a crust, where Maillard browning and texture develop; the core stays near 100 °C while it retains water, so it cooks by steaming. Frying can be described in stages: initial heating without boiling, surface boiling with vigorous bubbling, falling rate as the crust thickens and resists moisture loss, and the end point, when bubbling nearly stops.
Frying is a coupled heat and mass transfer process: water leaves as steam and oil enters. Water loss and crust formation proceed together; the rate depends on oil temperature, product thickness, initial moisture and porosity. Oil temperature is a key control: too low a temperature lengthens frying time and increases oil uptake and pale colour; too high a temperature burns the surface before the core is cooked, increases acrylamide and accelerates oil degradation. Vacuum frying, at reduced pressure, lowers the boiling point of water and allows frying at lower temperatures, about 90 to 120 °C, preserving colour and nutrients and reducing acrylamide and oil degradation.
Most oil is not absorbed while food is in the fryer, when outward steam flow resists it, but during the short period after removal. As the product cools, steam in its pores condenses and the pressure falls, drawing surface oil into the crust by a vacuum effect and capillary action. Oil uptake therefore depends mainly on the amount of oil left on the surface and on the structure of the crust: products with high surface area, thin slices, high initial moisture and porous crusts take up more oil. Reducing oil content relies on raw materials with high solids, pre-drying or blanching, coatings that form films (such as hydrocolloids), correct frying temperature, and removing surface oil immediately by draining, shaking, centrifuging or hot air blowing. Oil content is calculated from mass balance: if 100 g of raw slices at 80 per cent moisture give chips with 2 per cent moisture and 35 per cent oil, the non-fat dry matter of 20 g makes up 63 per cent of the chip, so the chip weighs about 31.7 g and contains about 11.1 g of oil.
Frying oils degrade by hydrolysis, oxidation and polymerisation, forming free fatty acids, polar compounds, polymers and volatile products, with darkening, foaming, smoke and off-flavours; the chemistry is described in food-chemistry-major-constituents. Oil quality is monitored by total polar compounds, free fatty acids, colour and sensory checks. Many countries set a limit for total polar compounds above which oil must be discarded; FSSAI uses 25 per cent. Good practice includes choosing stable oils, maintaining correct temperatures, filtering out food particles, topping up with fresh oil, avoiding contact with copper and iron, covering fryers when idle and discarding oil before the limit is reached. Collection of used cooking oil for biodiesel is promoted in India and elsewhere to prevent its reuse in food.
A bread plant follows the process sequence: flour handling with silos, sifters and pneumatic conveying; ingredient weighing and water metering with temperature control; mixers, from spiral and horizontal mixers in craft and medium bakeries to high-speed mechanical development mixers in plant bakeries; dividers, which cut dough by volume and so depend on consistent dough density; rounders; intermediate proofers; moulders, which sheet, curl and roll dough into shape; panning; final proofers with controlled temperature and humidity; ovens (deck, rack, reel, tunnel or travelling-tray); depanners; coolers, often spiral or ambient conveyors; slicers; and baggers. Biscuit lines add sheeters, gauge rolls, laminators, rotary cutters and moulders, wire-cut and depositing machines, long band ovens, oil sprayers, coolers, stackers and packaging machines. Snack plants use slicers, fryers with continuous oil filtration and heat exchangers, extruders, dryers, seasoning drums and form-fill-seal packaging with nitrogen flushing.
Equipment is designed and maintained for hygiene and safety: hygienic design that allows cleaning, metal detection or X-ray inspection after packing, guarding of moving parts, dust control because flour dust is both an explosion hazard and a cause of baker's asthma, and control of oven and fryer temperatures. Energy is a large cost, especially for ovens and fryers, so heat recovery is common in large plants.
Quality control in bakery and snack plants combines raw material testing, process control and finished product evaluation. Flour is tested for moisture, protein, gluten, falling number and rheology (cereal-science-milling); fats for solid fat content and oxidation; potatoes for specific gravity and reducing sugars; and other ingredients against specifications. In process, dough temperature, mixing energy or time, proof time and temperature, oven profiles, frying temperature and oil quality, and product moisture are monitored.
Finished bread is assessed by weight, volume and specific volume (loaf volume divided by weight; a 480 g loaf of 2,400 cm³ has a specific volume of 5.0 cm³/g), measured by seed displacement or laser scanning; crust colour; symmetry; crumb grain, cell size and uniformity, assessed by scoring or image analysis; crumb firmness by texture analyser over storage, to follow staling; moisture and water activity; and sensory evaluation. Biscuits are checked for dimensions, weight, moisture, colour and breaking strength; pasta for colour, specks, cooking quality; and snacks for moisture, oil content, salt, colour, breakage and acrylamide. Microbiological checks focus on mould and rope in bread and on hygiene indicators and pathogens in fillings and ingredients. Bake tests of flour and pilot trials of new formulations link ingredient quality to performance, and statistical process control charts help keep weights and other parameters within specification, which also matters for legal metrology requirements on declared net quantity.
A student uses this subject to connect cereal chemistry with real products. The calculations recur in exams and in the pilot bakery: baker's percentages, desired dough temperature, baking loss, specific volume, spread ratio and oil content by mass balance. Baking the same bread by straight dough and sponge-and-dough, or frying chips from cold-stored and reconditioned potatoes, shows the principles more clearly than any text.
Five years into a bakery, biscuit, pasta or snack plant, a technologist adjusts formulas to new flour lots, sets mixing, proof and oven conditions, troubleshoots defects such as low volume, collapsed cakes, checking, sticky pasta or dark chips, manages frying oil quality and acrylamide mitigation, extends shelf life against staling and mould, develops reduced-salt, reduced-sugar or whole-grain products, and keeps weights and labels compliant.
A senior technical or operations manager with twenty-five years' experience designs plants and product ranges, chooses processes such as Chorleywood or sponge-and-dough, frozen or fresh distribution, and fried or baked snacks, manages large-scale reformulation programmes for health targets, oversees supplier quality for flour, fats and potatoes, and leads compliance with additive, contaminant and labelling law across markets.
A researcher at this level studies the mechanisms behind product quality: gas cell formation and stabilisation, starch-protein interactions in staling, enzyme action in dough, structure of gluten-free systems, heat and mass transfer in baking and frying, oil uptake and its reduction, acrylamide formation and mitigation, and the digestibility and health effects of bakery products. Such work combines rheology, materials science, chemistry and engineering.
This manual gives principles, typical ranges and calculations rather than complete commercial formulations, which vary widely by product and market. Permitted improvers, additives and their levels differ between countries and must be checked in current regulations. Confectionery, chocolate and sugar boiling are covered in another subject; flour testing and milling in cereal-science-milling; starch, protein and frying oil chemistry in food-chemistry-major-constituents; acrylamide in food-toxicology-contaminants-allergens; and rope and mould spoilage in food-microbiology. Detailed oven and fryer engineering design is only introduced.
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