Food Science & Technology · Commodity Processing Technologies · also Sugar Technology, Confectionery Technology, Chocolate Technology
Making sugar from cane and beet, non-centrifugal sugars such as jaggery, alternative sweeteners, and the sugar and chocolate confectionery built on them.
In the exams: ICAR AIEEA-PG Code 18 Unit III (sugars and sweets); GATE XE-G Section 3 (cocoa); ICAR AICE 35.a Unit 2 (confectionery products)
Sugar technology begins in the cane field and the beet field and ends in a sweet shop. Between them lie some of the largest and oldest food industries in the world: the extraction and crystallisation of sucrose, the refining of raw sugar to white, the village production of jaggery, the conversion of starch to glucose and high-fructose syrups, the search for sweeteners with fewer calories, and the craft and science of confectionery and chocolate. All of them rest on the same physical chemistry: how much sucrose water can hold at a given temperature, when a supersaturated solution crystallises and when it sets into a glass, how sugars invert and brown when heated, and how fats crystallise.
This manual follows that chain. It begins with cane and beet as raw materials and with the factory processes that turn their juice into crystal sugar and by-products, then covers refining, non-centrifugal sugars, starch-derived syrups and alternative sweeteners. The second half covers sugar confectionery (hard-boiled sweets, toffees, fondants, gums and jellies), chocolate manufacture from cocoa mass to tempered bar, the two kinds of bloom, and the quality and shelf life of confectionery. The chemistry of sugars and the Maillard reaction is covered in food-chemistry-major-constituents, the rheology of chocolate and syrups in food-physical-properties-rheology, evaporator design in evaporation-dehydration, and cocoa fermentation, drying, roasting and pressing in beverage-technology; they are referred to here, not repeated.
The subject is examined in ICAR AIEEA-PG Code 18 Unit III (sugars and sweets), GATE XE-G Section 3 (cocoa and plantation products) and ICAR AICE 35.a Unit 2 (confectionery products), and it is the daily work of technologists in sugar mills, refineries, starch plants and confectionery factories everywhere. Sugar factories in India, Brazil, Thailand and Australia work mainly with cane; those in Europe and North America mainly with beet; confectionery and chocolate are made worldwide. Product definitions and permitted sweeteners differ by country, and this manual says so where it matters.
Sucrose is made commercially from two plants. Sugarcane (Saccharum species hybrids) is a tropical and subtropical grass; its stalk stores sucrose in the juice of the parenchyma cells surrounded by fibrous tissue. Sugar beet (Beta vulgaris) is a temperate biennial whose swollen root stores sucrose. Roughly three-quarters or more of world sugar comes from cane, the rest from beet, though the share changes with seasons and policy.
Mature cane is mostly water. Its sucrose content is commonly in the range of about 10–15% of cane weight and its fibre about 11–16%, varying with variety, age, climate and harvest; the remaining soluble solids, the non-sucrose, include reducing sugars (glucose and fructose), salts, organic acids, proteins, gums and waxes. Beet typically contains more sucrose, commonly about 15–20% of root weight, and less fibre, but more nitrogenous and other non-sugars that must be removed in clarification. Both crops are harvested at the peak of sucrose accumulation and processed as fast as possible, because sucrose begins to be lost from the moment of harvest.
Sugar technologists describe juice by three numbers. Brix is the percentage by mass of total dissolved solids, measured by refractometer or hydrometer; strictly it is the mass percentage of sucrose in a pure sucrose solution of the same refractive index or density, so for impure juice it is an apparent value. Pol is the apparent sucrose content measured by polarimetry: sucrose rotates plane-polarised light to the right, and the reading is converted to sucrose percentage; other optically active substances such as glucose and fructose disturb it, which is why it is called apparent sucrose. Purity is pol as a percentage of Brix. A juice of 18 °Brix and 15.3 pol has a purity of 15.3 ÷ 18 × 100 = 85.0. High purity means more sucrose can be crystallised and less is lost to molasses.
Factories also report sugar recovery, the mass of sugar made per 100 of cane crushed. It depends on the cane's pol, the efficiency of extraction and the losses in bagasse, filter cake and final molasses. Payment of growers in many countries is linked to cane weight and, increasingly, to cane quality measured as sucrose or recoverable sugar.
Cut cane deteriorates quickly. The stalk keeps respiring, its own invertase and acid hydrolysis invert sucrose to glucose and fructose, and bacteria entering through cut ends and damage, especially Leuconostoc mesenteroides, convert sucrose into dextran, a polysaccharide that raises juice viscosity, slows filtration and crystallisation, distorts crystal shape and inflates pol readings. Losses grow with time from cut to crush, temperature, the extent of damage from mechanical harvesting and burning, and with stale or chopped billets. Good practice keeps the cut-to-crush interval short, typically aiming for well under a day, crushes cane in the order it was cut, and keeps cane yards clean.
Beet is stored in large piles before processing because the campaign is longer than the harvest. Respiration consumes sucrose during storage, more so if roots are damaged, warm or frozen and thawed, so piles are ventilated and cooled where climate allows. In both crops, every hour of delay converts sucrose that could have been crystallised into reducing sugars that end up in molasses.
Cane arriving at the factory is cut by revolving knives and shredded to open the juice cells. Juice is then extracted either by a milling tandem or by a diffuser. A milling tandem is a series of mills, each with three or more heavy grooved rollers, through which the shredded cane passes in turn. Because dry crushing alone leaves much sucrose in the fibre, water is added to the bagasse before the last mill, and the thin juice from each mill is returned to the bagasse ahead of the previous mill; this is compound imbibition. In a cane diffuser, shredded cane moves slowly through a long bed while hot water and recirculated juice percolate through it counter-currently, leaching sucrose; the residue is then dewatered in mills. Beet is sliced into thin strips called cossettes and extracted in counter-current diffusers with hot water.
Extraction efficiency is the proportion of sucrose in cane that reaches mixed juice. The residue leaving the last mill is bagasse, the main fuel of the factory. More imbibition water raises extraction but also raises the water that must later be evaporated, so the amount is an economic balance.
Mixed juice is turbid, acidic and contains soil, wax, proteins, gums and colloids. Clarification removes these and raises the pH to about neutral to limit inversion during heating. In defecation, the simplest method, the juice is heated and limed with milk of lime; calcium phosphate and calcium salts precipitate and carry down suspended matter, and the mud is settled in a clarifier. The settled mud is filtered in rotary vacuum filters, giving filtrate that returns to process and filter cake (press mud).
In India most factories make plantation white sugar directly from cane by double sulphitation: juice is treated with lime and sulphur dioxide, and the syrup is sulphited again after evaporation. The sulphur dioxide reduces colour and the calcium sulphite precipitate helps clarification. In carbonation, used in beet factories and some cane factories, large doses of lime are added and then precipitated with carbon dioxide as calcium carbonate, which adsorbs colour and non-sugars well; this gives whiter sugar but needs a lime kiln and produces more mud. The choice of process decides whether a mill makes raw sugar for refining or a direct white sugar.
Clear juice of roughly 13–16 °Brix is concentrated in multiple-effect evaporators, commonly four or five effects in series, to a syrup of about 60–65 °Brix. Steam heats the first effect, and the vapour from each effect heats the next, at successively lower pressure; this reuses energy several times. The mass balance is on solids: 100 t of juice at 15 °Brix gives 100 × 15 ÷ 60 = 25 t of syrup at 60 °Brix, so 75 t of water is evaporated. Evaporator design is covered in evaporation-dehydration.
Syrup is boiled further, under vacuum at moderate temperature to limit colour and inversion, in single-effect vacuum pans until it is supersaturated. Seed crystals, fine sugar slurried in alcohol or a magma of small crystals, are introduced in the metastable zone, where existing crystals grow but new ones do not form spontaneously. Syrup is fed while the crystals grow, and the boiled mixture of crystals and mother liquor, the massecuite, is discharged to crystallisers, where cooling and stirring let more sucrose deposit. Centrifugals then separate crystals from mother liquor (molasses), and the crystals are washed and dried. Because one boiling cannot recover all the sucrose, factories use a multi-boiling scheme, commonly a three-massecuite (A, B, C) system: the molasses from A is boiled again to B, and from B to low-grade C, whose sugar is used as seed or remelted. The final mother liquor, from which no more sugar is economically recovered, is final molasses.
Raw cane sugar is brown and sticky because each crystal carries a film of molasses and some colour within the crystal. Refineries convert it to white sugar of very high purity. The first step is affination: raw sugar is mingled with a warm saturated syrup and centrifuged, so that the outer molasses film is washed off without dissolving the crystal. The washed sugar is melted in hot water to a liquor, which is clarified by phosphatation (lime and phosphoric acid forming a calcium phosphate floc, removed by flotation) or by carbonatation (lime and carbon dioxide, with filtration of the calcium carbonate). Colour is then removed by activated carbon, bone char or ion-exchange resins. The decolourised fine liquor is boiled in vacuum pans, often in several strikes, to white crystals that are centrifuged, washed, dried, cooled, screened and conditioned before storage.
Colour of sugar and liquors is measured in ICUMSA units, by absorbance at 420 nm of a filtered solution at a stated pH and concentration; lower numbers mean whiter sugar. The International Commission for Uniform Methods of Sugar Analysis (ICUMSA) publishes the methods used worldwide for pol, colour, moisture, ash and other sugar tests.
Refined and semi-refined sugars are sold in many forms. Granulated sugar is graded by crystal size; caster sugar is finer and dissolves quickly, suiting baking and beverages. Icing or powdered sugar is milled to a fine powder and usually mixed with a small proportion of starch or another anti-caking agent, because fine sugar absorbs moisture and cakes. Cube sugar is moistened granulated sugar pressed or moulded and dried. Brown sugars are either made by coating white crystals with molasses or cane syrup, or produced directly as low-grade crystals that keep part of their molasses; their colour, flavour and moisture rise with molasses content. Demerara-style and turbinado-style sugars are large-crystal, partly washed cane sugars. Liquid sugar is a refined sucrose solution, sometimes partly inverted, delivered by tanker to beverage and food plants that would otherwise dissolve granulated sugar. Organic sugar is made from organically grown cane under certification rules. The names and specifications of these products are commercial or national; the same name can describe different products in different countries.
Freshly dried sugar still releases moisture from within the crystals and from the thin syrup film between them for some days. If it is packed and stored at once, this moisture migrates and the sugar sets into hard lumps. Sugar is therefore conditioned, held in silos with controlled, dry, cool air until it reaches equilibrium, before bulk storage or bagging. Stored sugar should be kept at low relative humidity: sugar takes up moisture when the air is humid and gives it up when the air is dry, and repeated cycles cement crystals together. Fine sugar dust is a serious explosion hazard in conveyors, silos and grinding rooms, so dust control, earthing and ignition control are essential in sugar handling. Sugar quality for industrial users is specified by colour, ash (conductivity ash), moisture, particle size, sulphite content where relevant, and microbiological counts for sensitive uses such as beverages and canned foods.
Non-centrifugal sugar (NCS) is the general name, used by FAO and others, for sugar made by evaporating cane juice to a solid without separating the molasses in a centrifuge. Because the molasses stays in the product, NCS keeps the minerals, reducing sugars and colour of the juice. Jaggery or gur in South Asia, panela in Latin America and kokuto in Japan are examples; muscovado is a similar product, often a soft, moist, dark sugar. Khandsari is an intermediate: juice is boiled in open pans to a massecuite that is crystallised and then separated in small centrifuges, so it is a centrifugal sugar made by an open-pan, small-scale process. India is among the largest producers and consumers of jaggery, and much of it is made in small rural units close to the cane fields.
Jaggery is mostly sucrose, with invert sugar, moisture and a few per cent of minerals and other non-sugars. Its composition varies widely with cane variety, juice quality, clarification and boiling. It is sold as blocks, granules (powdered jaggery) and liquid jaggery.
Fresh cane juice, extracted in small crushers, is strained and heated in a series of open pans, often on a multiple-pan furnace fired with bagasse. As the juice heats, scum rises and is removed. Clarification is helped by vegetable clarificants, the mucilaginous extracts of plants such as okra or other malvaceous species, which bind impurities into the scum; lime is used in small amounts to adjust acidity, and the use of chemical clarificants such as hydrosulphite to whiten jaggery is restricted or discouraged in many places because of residues. Boiling continues until the concentrated mass reaches the striking point, judged by temperature (commonly around 118–120 °C) and by the behaviour of a sample dropped into water. The mass is then cooled and stirred in a trough, and poured into moulds or worked into granules.
Yield follows the solids balance. If 100 kg of juice at 18 °Brix is boiled to jaggery of 10% moisture, ignoring losses in scum, the jaggery mass is 100 × 0.18 ÷ 0.90 = 20 kg.
Good jaggery is light golden to brown, hard, crystalline in texture, sweet with no salty or bitter taste, and low in moisture and impurities. Dark colour results from poor clarification, high reducing sugars in stale juice, and overheating. Jaggery is hygroscopic because of its invert sugar and salts; in humid monsoon storage it absorbs water, softens, darkens and becomes liable to fermentation and mould growth. Storage in moisture-proof packaging, in dry stores, and making jaggery with lower initial moisture all help. Granular jaggery dried to low moisture keeps better than block jaggery. Liquid jaggery is a concentrated syrup preserved by its high solids, sometimes with permitted preservatives. Improved plants with better furnaces, steam heating, stainless steel pans and hygienic handling have been developed to raise fuel efficiency and product quality, but much jaggery is still made in traditional units, which is why quality varies so widely. Buyers therefore test colour, moisture, sucrose and reducing sugars, insoluble matter and sulphur dioxide residue where it is regulated.
Final molasses is the dark, viscous mother liquor left after the last crystallisation, from which no more sucrose can be crystallised economically. It still contains a large amount of sugar, sucrose and reducing sugars together commonly around half of its mass, together with water, ash and organic non-sugars; composition varies with cane, process and country. Molasses is one of the most valuable by-products of the industry. Its main uses are as the fermentation substrate for ethanol (potable alcohol and fuel ethanol) and for baker's yeast, citric acid and other fermentation products, as an ingredient of animal feed, and in some food uses. Beet molasses is used similarly but differs in composition, with more betaine and different salts.
The ethanol obtainable follows the Gay-Lussac stoichiometry, 0.511 g of ethanol per g of hexose at the theoretical maximum. One tonne of molasses with 50% fermentable sugar expressed as hexose could give at most 1000 × 0.5 × 0.511 = 256 kg of ethanol, about 324 L at a density of 0.789 g/mL; at 90% fermentation efficiency, about 292 L. Real distillery yields are lower and are stated per tonne of molasses of specified quality.
Bagasse is the fibrous residue left after juice extraction. It leaves the mills at roughly 50% moisture and amounts to about a quarter to a third of the cane weight. Its fibre content means it can be estimated from the cane fibre: if 1000 t of cane contains 13% fibre and the bagasse is 48% fibre, the bagasse mass is 130 ÷ 0.48 = about 271 t. Most bagasse is burned in the factory's boilers to raise steam for the evaporators and pans and electricity for the mills; modern factories with high-pressure boilers export surplus electricity to the grid (cogeneration). Bagasse is also a raw material for paper and board, particleboard, moulded tableware, furfural and, increasingly, second-generation ethanol and other bio-based products. The more steam the factory saves in evaporation and boiling, the more bagasse or electricity is left for sale. Stored bagasse must be kept from heating and fermenting in large piles, and its fine dust is a respiratory hazard for workers, so storage and handling are managed as carefully as for any fuel.
Press mud, also called filter cake or filter mud, is the solid separated from the clarifier mud by filtration. It contains fibre, wax, coagulated proteins, calcium and phosphate salts and some sugar, and it is produced at a few per cent of the cane weight. It is widely used as an organic manure and soil amendment, often after composting with distillery effluent; cane wax can be extracted from it. Other residues include cane tops and trash from the field, used as fodder or fuel, and from beet factories, beet pulp (dried and pelleted as feed) and lime sludge from carbonation.
Distillery effluent (spent wash or vinasse) from molasses fermentation is a concentrated, dark, acidic liquid with a very high organic load and is one of the most difficult agro-industrial effluents. It is treated by anaerobic digestion to biogas, concentration and incineration, composting with press mud, or controlled land application where regulations allow. Integrated sugar complexes that produce sugar, power, ethanol and compost from one crop are now common in cane-producing countries.
Glucose syrups are concentrated solutions of the products of starch hydrolysis: glucose, maltose and higher oligosaccharides. They are made from maize, wheat, potato, cassava and other starches. Acid hydrolysis was the original method; most syrups are now made enzymatically. In liquefaction, a thermostable α-amylase breaks a gelatinised starch slurry at high temperature into dextrins; in saccharification, glucoamylase (and for maltose-rich syrups, β-amylase or other maltogenic enzymes) converts the dextrins into the desired sugar profile. The syrup is refined by filtration, carbon and ion exchange and concentrated.
The degree of hydrolysis is expressed as dextrose equivalent (DE): the reducing sugar content, calculated as dextrose (glucose), as a percentage of the dry solids. Starch has a DE near 0 and pure dextrose 100. A syrup with 80% solids whose reducing sugars, as dextrose, amount to 33.6 g per 100 g of syrup has a DE of 33.6 ÷ 80 × 100 = 42. As DE rises, sweetness, hygroscopicity, browning, fermentability and freezing-point depression rise, while viscosity and the ability to prevent sucrose crystallisation and to give body fall. Maltodextrins are products of DE below 20; syrups of DE about 42 are the classic confectionery glucose syrups.
Invert sugar is the equimolar mixture of glucose and fructose formed when sucrose is hydrolysed. The name comes from the change in optical rotation: sucrose rotates polarised light to the right, while the mixture rotates it to the left because fructose is strongly laevorotatory. Inversion is done with acid and heat or with the enzyme invertase. Water is added in the reaction, so the mass of sugar rises: 342 g of sucrose gives 360 g of invert sugar, a factor of 1.053, and 100 kg of sucrose fully inverted gives about 105.3 kg of invert sugar.
Invert sugar is more soluble than sucrose, so a mixture of sucrose and invert sugar can be held at higher total solids without crystallising; it is somewhat sweeter than sucrose on a dry basis, more hygroscopic, browns more readily, and lowers water activity. These properties are why partial inversion is welcome in jams, why invertase is added to fondant centres so they liquefy after enrobing, and why invert syrups keep cakes and fillings moist. Uncontrolled inversion during boiling, however, makes confectionery sticky.
High-fructose syrups (HFS; high-fructose corn syrup, HFCS, when made from maize, and isoglucose in some regulations) are made from high-glucose syrup by glucose isomerase, usually immobilised in packed columns, which converts part of the glucose to fructose. Equilibrium limits the conversion to about 42% fructose on a dry basis, giving the first-generation HFS-42. Chromatographic separation produces a fraction enriched to about 90% fructose, and blending this with HFS-42 gives HFS-55, which matches sucrose sweetness in soft drinks. The blend proportions follow a simple balance on fructose: to make HFS-55 from HFS-90 and HFS-42, the fraction of HFS-90 on a dry basis is (55 − 42) ÷ (90 − 42) = 27.1%.
High-fructose syrups are liquid, easy to handle and cheaper than sucrose where maize is subsidised or abundant, so they replaced much sucrose in North American soft drinks; their use in other regions is limited by quotas, prices and consumer preference. Nutritionally, HFS-55 and sucrose supply similar amounts of glucose and fructose.
Sugar alcohols, or polyols, are made by hydrogenating the carbonyl group of a sugar to an alcohol group: sorbitol from glucose, mannitol from mannose or fructose, xylitol from xylose, maltitol from maltose, lactitol from lactose, and isomalt from isomaltulose. Erythritol is made by fermentation. Polyols are bulk sweeteners: they replace sucrose weight for weight and supply body, but most are less sweet than sucrose; xylitol is close to sucrose in sweetness and erythritol and sorbitol are less sweet. They are not fermented by oral bacteria to acids, so they are non-cariogenic and are used in sugar-free chewing gum and sweets. They are partly absorbed, so their energy value is lower than sugar's, and they do not raise blood glucose as much. Because unabsorbed polyols reach the large intestine, large intakes cause laxation and flatulence, and many regulations require a warning on products with a high polyol content. Xylitol and erythritol have a strongly negative heat of solution and give a cooling sensation in the mouth, used in mint confectionery. Polyols do not take part in Maillard browning, which changes colour and flavour in baked and boiled products.
High-intensity sweeteners are used at very low concentrations because they are many times sweeter than sucrose. Relative sweetness depends on concentration, temperature and the food, so published figures are approximate. Commonly quoted values are: saccharin about 300–500 times sucrose, with a bitter aftertaste at high levels; aspartame about 200 times, a dipeptide methyl ester that breaks down with heat and in neutral pH and contains phenylalanine, so products must carry a warning for people with phenylketonuria; acesulfame potassium about 200 times, heat-stable, often blended with aspartame for synergy; sucralose about 600 times, a chlorinated sucrose that is heat- and acid-stable; steviol glycosides from Stevia rebaudiana leaves, roughly 200–300 times, with liquorice or bitter notes at high levels; and neotame and advantame, derivatives of aspartame thousands of times sweeter. The amount needed to replace sugar follows from the sweetness factor: if sucralose is taken as 600 times as sweet as sucrose, replacing 100 g of sugar in a litre of drink needs 100 ÷ 600 = 0.17 g of sucralose, and the lost bulk and body must be made up with other ingredients.
Every sweetener used in food must be approved by the national authority, which sets the foods in which it may be used and the maximum levels. Safety assessment by JECFA (the Joint FAO/WHO Expert Committee on Food Additives) and by regional bodies establishes an acceptable daily intake for each; the approved list and use levels differ between countries and are revised, so a technologist checks the current regulation of each market rather than relying on a textbook list. Labelling rules also differ: phenylalanine warnings for aspartame, laxative warnings for polyols, and the declaration of sweeteners by name or code are common requirements.
In formulation, removing sugar removes more than sweetness. Sugar provides bulk, body, viscosity, water binding (lower water activity), browning, crystallisation behaviour and preservation. Sugar-free confectionery therefore uses polyols for bulk with high-intensity sweeteners for sweetness, and sugar-reduced beverages use blends of sweeteners and flavour modifiers to approach the taste and mouthfeel of the original. Temporal profile, the time to peak sweetness and the lingering aftertaste, is often the hardest property to match.
Most sugar confectionery starts by dissolving sucrose and glucose syrup in water and boiling the mixture to remove water. As water is boiled off, the boiling point rises, so the temperature reached tells the confectioner the solids content: a syrup boiling at about 115 °C is still soft and moist, one at about 150 °C has very little water left. Each product is cooked to its own temperature, adjusted for altitude. Pure sucrose syrups at such concentrations crystallise easily, so a doctor is added to control crystallisation: glucose syrup, which adds dextrins and other sugars that hinder sucrose crystallisation and add viscosity, or invert sugar or an acid such as cream of tartar that inverts some sucrose during boiling. The amount of doctor sets whether the product will be a clear glass, a fine crystalline mass or a sticky mass.
The solids balance of a batch follows simply. A batch of 100 kg sugar, 60 kg glucose syrup of 80% solids and 30 kg water contains 148 kg of solids; cooked to 98% solids it gives 148 ÷ 0.98 = 151 kg of candy, so about 39 kg of water is evaporated.
Hard-boiled sweets are sucrose and glucose syrup cooked to very low moisture, commonly 2–3% or less, at temperatures around 145–155 °C, often under vacuum to reduce colour and inversion, then cooled on a slab, mixed with acid, colour and flavour, formed and wrapped. The product is an amorphous glass, a supercooled liquid so viscous that it behaves as a solid below its glass transition temperature. It is clear because it has no crystals. If it picks up water from the air, its glass transition temperature falls, the surface becomes sticky, and sucrose can crystallise (graining), turning the sweet opaque and grainy. Hard candy is therefore wrapped and packed against moisture.
Toffees and caramels contain milk solids (or condensed milk) and fat as well as sugars. They are cooked to lower temperatures than hard candy, roughly 115–130 °C depending on the texture wanted, leaving more moisture, so they are chewy rather than glassy. The characteristic flavour and colour come from Maillard reactions between milk proteins and reducing sugars and from caramelisation; the milk protein also emulsifies the fat. Fudge is a caramel that has been made to crystallise (grained) deliberately, by beating or by adding fondant, to give a short, crumbly texture.
Fondant is a mass of very fine sucrose crystals in a saturated syrup. Sugar and glucose syrup are cooked to about 115–120 °C, cooled, and then beaten vigorously so that sucrose crystallises rapidly into many tiny crystals, giving a smooth, white, plastic mass. Fondant is used for creams and centres; with invertase added, a firm fondant centre becomes soft and liquid some days after it has been enrobed in chocolate.
Gums and jellies are sugar–glucose syrups set with a hydrocolloid: gelatin for elastic, chewy gums; pectin for short, clean-biting fruit jellies; starch (often moulded in starch trays, the mogul process, and stoved to the right moisture); and gum arabic for the hard pastilles of traditional confectionery. Their moisture is higher than that of hard candy, so water activity and shelf life depend on high soluble solids and good packaging. Aerated confectionery such as marshmallow and nougat whips air into a sugar syrup stabilised by gelatin, egg albumen or other proteins. Panning builds layers of sugar or chocolate on centres in rotating pans: hard panning with repeated thin coats of sucrose syrup gives a crisp shell, soft panning with glucose syrup and powdered sugar a softer one.
Chocolate is a suspension of fine solid particles, sugar, cocoa solids and in milk chocolate milk solids, in a continuous phase of fat, mainly cocoa butter. Cocoa beans are fermented, dried, roasted, winnowed to nibs and ground to cocoa mass (cocoa liquor), which is roughly half fat; part of the mass is pressed to cocoa butter and cocoa cake. Those steps are covered in beverage-technology. Dark chocolate is made from cocoa mass, sugar and added cocoa butter; milk chocolate adds milk powder or milk crumb; white chocolate contains cocoa butter, sugar and milk solids but no non-fat cocoa solids. The fat content of a recipe follows from its parts: a dark chocolate of 40% cocoa mass containing 55% fat, 10% added cocoa butter and 50% sugar contains 0.40 × 55 + 10 = 32% fat, and its total cocoa solids are 50%.
Legal definitions differ between countries in the minimum cocoa solids, milk solids and cocoa butter required for each category, and in whether vegetable fats other than cocoa butter may be used. The European Union, for example, permits up to 5% of specified vegetable fats in chocolate with labelling; other markets differ. The ingredients are mixed into a paste of the right fat content for refining.
Refining reduces the particle size of sugar and cocoa solids so the chocolate feels smooth. On a five-roll refiner the paste passes between successively faster rolls and leaves as a thin flaky powder. The largest particles should be small enough not to be felt; a maximum particle size of roughly 20–30 µm is commonly targeted, and coarser chocolate feels gritty, while very fine chocolate becomes thicker because more particle surface must be coated with fat. Ball mills and other mills are also used.
Conching is a prolonged mixing and kneading of the refined chocolate at elevated temperature, for hours to a day or more depending on the equipment and product. It has three main effects: it drives off moisture and undesirable volatile acids such as acetic acid from fermentation, developing a smoother, rounder flavour; it coats the particles with fat and breaks up agglomerates; and it turns the dry flakes into a fluid liquid with the flow properties needed for moulding or enrobing. Emulsifiers are added toward the end: lecithin lowers the plastic viscosity and saves cocoa butter, and polyglycerol polyricinoleate (PGPR) lowers the yield value. Molten chocolate is a non-Newtonian fluid with a yield stress; its flow is commonly described by the Casson model, as covered in food-physical-properties-rheology.
Cocoa butter is polymorphic: it can crystallise in six forms, numbered I to VI in order of increasing stability and melting point. Form V (often called βV) melts at about 33–34 °C, just below mouth temperature, and gives chocolate its gloss, snap, contraction from the mould and resistance to bloom. Untempered chocolate solidifies in unstable forms, looks dull and streaky, is soft and blooms quickly. Tempering is the controlled pre-crystallisation that ensures the chocolate sets in form V.
A typical temper for dark chocolate melts all crystals at about 45–50 °C, cools the chocolate with stirring to about 27–28 °C so that crystals of several forms nucleate, then reheats it slightly to about 31–32 °C to melt the unstable forms and leave only form V seed crystals. Milk chocolate is tempered at lower temperatures, because milk fat softens cocoa butter; exact temperatures depend on the recipe and machine. Seeding with finely divided form V cocoa butter or tempered chocolate is an alternative. Temper is checked with a temper meter, which records the cooling curve, and by the gloss and snap of a test piece. Compound coatings made with lauric fats such as palm kernel or coconut fat do not need tempering, which is one reason they are used for cheaper coatings; they are not compatible with cocoa butter in large proportions.
Bloom is a whitish or greyish surface film that spoils the appearance of chocolate. Fat bloom is caused by fat crystals at or near the surface that scatter light. It appears as a grey, dull film or streaks that feel greasy and melt when touched. Its main causes are poor tempering, which leaves unstable crystals that transform with time; the slow transformation of form V to the more stable form VI during storage, especially under fluctuating temperatures; storage at warm temperatures that melt part of the fat, which then recrystallises at the surface; and migration of liquid oils from centres such as nut pastes, pralines and fillings into the chocolate shell, which softens the cocoa butter and carries it to the surface.
Fat bloom is prevented by good tempering, cool and constant storage temperature (commonly about 15–18 °C), avoiding temperature cycling during distribution, using fats in centres that are compatible with cocoa butter or barrier layers between filling and shell, and adding bloom-retarding fats such as milk fat or specific hard fats in the recipe.
Sugar bloom has a different cause. When cold chocolate is brought into warm, humid air, water condenses on its surface, or chocolate is stored in high humidity. The water dissolves sugar from the surface; when it later evaporates, the sugar recrystallises as a dry, rough, white layer of fine crystals. Unlike fat bloom, sugar bloom feels rough and dry and does not melt when touched, and it dissolves if a drop of water is placed on it. It is prevented by storing chocolate at moderate humidity, by bringing cold chocolate up to room temperature in its sealed packaging before unwrapping, and by avoiding chilling in domestic refrigerators followed by exposure to humid air.
The two kinds of bloom can be told apart in the laboratory by touch, by solvent tests, and by examination of the surface; X-ray diffraction identifies the crystal forms of the fat. Both are quality defects rather than safety hazards: bloomed chocolate is safe to eat, but customers reject it, so bloom is one of the main causes of complaints and returns in the chocolate trade.
In a factory, bloom complaints are traced through the life of the product. A fresh product that blooms within days points to poor temper or to cooling that was too fast or too slow in the cooling tunnel. Bloom that appears after weeks in filled products points to oil migration from the filling, and its speed rises with storage temperature. Bloom after distribution in summer points to warm storage or temperature cycling in the supply chain. Sugar bloom points to condensation at some step, for example cold-chain products unloaded in a humid warehouse, or moulds and products cooled below the dew point of the packing room. Corrective actions include adjusting the tempering machine and cooling tunnel profile, reformulating fillings, adding barrier layers, changing packaging and specifying storage conditions to distributors and retailers. Compound coatings are less prone to classic fat bloom but can show their own surface defects. Keeping a record of storage temperatures in the supply chain, for example with data loggers in shipments, turns many disputed complaints into clear findings.
Confectionery covers a wide range of water contents and textures, and its shelf life depends on keeping each product in its own state. Water activity (aw), the ratio of the vapour pressure of water in the food to that of pure water, controls microbial growth and the direction of moisture movement. Hard candy and chocolate have very low water activity; gums, jellies, fondants and marshmallows have intermediate values; and the difference between a product and the surrounding air decides whether it gains or loses moisture. A product with low aw stored in humid air picks up water and becomes sticky; a moist product in dry air dries out and hardens.
Many confections are amorphous rather than crystalline. An amorphous sugar glass is stable while its storage temperature stays below its glass transition temperature (Tg); water acts as a plasticiser and lowers Tg, so moisture uptake moves the product into the rubbery state, where it becomes sticky, flows (cold flow) and can crystallise. Composite products such as filled chocolates, wafers with creams and coated nuts suffer moisture and fat migration between components with different aw and fat phases, which softens crisp parts and hardens soft ones.
High sugar content prevents most bacterial growth, but not all spoilage. Osmophilic (xerophilic) yeasts, notably Zygosaccharomyces rouxii, can grow at the intermediate water activity of fondant centres, marzipan, fruit fillings and syrups, causing fermentation, gas and bursting of chocolates. Moulds can grow on the surface of products with intermediate aw, especially where condensation occurs. Fat-containing products such as toffees, nut confectionery and chocolate develop oxidative or hydrolytic rancidity; milk chocolate and nut pastes are particularly vulnerable, and lauric fats can give a soapy taste if lipase from contaminated ingredients acts on them.
Salmonella is the main microbial hazard in chocolate and cocoa products. It does not grow at their low water activity, but it can survive for long periods and is markedly more heat-resistant in a dry, fatty matrix than in moist foods, so a very small number of cells in raw cocoa, milk powder or nuts can cause outbreaks. Control relies on validated roasting of beans and heat treatment of other ingredients, strict separation of raw and roasted areas, dry cleaning and the prevention of water in the plant, and environmental monitoring. Allergens, especially milk, nuts, peanuts, soy and wheat, are a major labelling and cross-contact issue on shared lines.
Packaging is chosen to keep each product at its own moisture and protect it from light, oxygen, odours and damage. Hard candies need individual twist-wraps or flow-wraps with good moisture barrier; chocolate needs a barrier to odours and light and protection from heat; fillings and nut products benefit from oxygen barriers or modified atmospheres. Shelf-life testing combines storage at the expected conditions with accelerated tests at higher temperature and humidity, but accelerated tests must be interpreted with care, because chocolate melts and sugar glasses cross their glass transition at temperatures that change the mechanism of deterioration.
Routine quality tests include moisture and water activity, sugar composition and reducing sugars, viscosity and yield value of chocolate, particle size by micrometer or laser diffraction, temper index, fat content, colour, texture analysis (hardness, snap, chewiness), sensory evaluation, and microbiological tests for Salmonella, yeasts and moulds. Defects such as graining, stickiness, cold flow, bloom, fermentation, rancidity and loss of flavour are recorded against storage time to set and verify the shelf life printed on the pack.
A student uses this subject to answer the sugar and confectionery questions that recur in food technology examinations: purity from Brix and pol, why double sulphitation gives plantation white sugar, what a massecuite and final molasses are, how invert sugar and glucose syrup act as doctors, what DE means, why chocolate is tempered and how fat bloom differs from sugar bloom. In the laboratory the same student measures Brix and pol, boils a fondant and a hard candy to their temperatures, tempers chocolate by hand, and works the mass balances for evaporation, jaggery yield and recipe composition.
Five years into a sugar mill, refinery or confectionery plant, a technologist runs and troubleshoots the process: keeps cut-to-crush time and dextran under control, sets lime and sulphur doses, follows pan boiling and molasses purity, or in a confectionery plant sets cook temperatures, doctor levels, tempering and cooling tunnel profiles. The same person investigates complaints of sticky sweets, grained toffee, bloomed chocolate or fermented centres, traces each to its cause, and checks that sweeteners, colours and labels comply with the market's current regulation.
After twenty-five years a senior manager decides how a sugar complex balances sugar, ethanol, power and compost from one crop, when to invest in cogeneration, refining or effluent treatment, and how to price cane quality. In confectionery, the senior manager leads sugar reduction programmes, approves new sweetener systems market by market, sets the controls that keep Salmonella out of a chocolate plant, and decides on recalls when an allergen or pathogen incident occurs. The same manager negotiates cane or cocoa supply contracts that reward quality, and answers to regulators and customers on sustainability and labour standards in the supply chain.
A researcher with long industry experience works on the science behind these decisions: crystallisation kinetics and crystal size control in pans, dextran and colour formation in juice, enzyme engineering for starch syrups and isomerisation, the molecular basis of cocoa butter polymorphism and bloom, structure–sweetness relationships and the temporal profile of new sweeteners, and the survival of pathogens in low-moisture foods. Such work produces the models and data that companies and regulators use to set process conditions and approve new ingredients.
This manual does not give the full engineering of mills, diffusers, pans and centrifugals, boiling-house material balances by the Cobenze or SJM formulas, or detailed pan-boiling schemes; it gives the principles and simple solids balances. It does not list approved sweeteners, their maximum use levels or ADIs for any country, or legal compositional standards for each chocolate category beyond the EU vegetable-fat example, because these differ by jurisdiction and change; the current regulation must be read. Distillery practice and ethanol yields per tonne of molasses are given only as theoretical stoichiometry. Cocoa bean fermentation, drying, roasting and pressing are in beverage-technology; sugar chemistry and the Maillard reaction in food-chemistry-major-constituents; chocolate and syrup rheology in food-physical-properties-rheology. Chewing gum base technology and detailed panning practice are covered only in outline.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions. Every numerical answer was computed by script. Process temperatures, compositions and sweetness factors are standard textbook values that vary with raw material, recipe and source; permitted sweeteners and legal standards differ by country.
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