Food Science & Technology · Commodity Processing Technologies · also Spice Processing, Flavour Technology, Plantation Crops Processing, Essential Oils and Oleoresins
Processing spices and herbs, extracting essential oils and oleoresins, and the technology of natural and synthetic flavours and food colours, including encapsulation and flavour stability.
In the exams: GATE XE-G Section 3 (spice; extraction of essential oils and oleoresins from spices); ICAR AIEEA-PG Code 18 Unit III (flavouring and pigment technology); ICAR AICE 35.a Unit 7
Spices, herbs, essential oils and flavours are used in small amounts but decide whether a food is eaten with pleasure or left on the plate. A spice is a dried plant part, such as a seed, fruit, bark, root, rhizome, flower bud or stigma, used mainly for flavour, colour or pungency rather than for nutrition; a herb is usually the leaf of a plant used the same way. Their value lies in a small fraction of the plant: the volatile oil that gives aroma, and non-volatile compounds that give pungency, bitterness and colour. Spice technology is the art of keeping those compounds through drying, cleaning, grinding and storage, of removing the microorganisms and contaminants that dried plant material picks up, and of extracting the flavour as essential oils and oleoresins that industry can dose exactly.
Flavour technology widens the field to the whole range of flavourings that the food industry uses: natural extracts, flavouring substances made by synthesis, process flavours made by heating sugars with amino acids, and smoke flavourings. Because flavour compounds are volatile and reactive, much of the technology is about protecting them, by encapsulation, by choice of carrier and packaging, and by understanding how they interact with the food. The same chapter of food science covers natural colours, which face the same problems of stability and regulation. The chemistry of the major food constituents is in food-chemistry-major-constituents; rheology and particle behaviour in food-physical-properties-rheology; methods of analysis in food-analysis; grinding equipment in mechanical-unit-operations; spray drying in evaporation-dehydration; and contaminant toxicology in food-toxicology-contaminants-allergens.
The subject is examined in GATE XE-G and XL-U Section 3 (spices, extraction of essential oils and oleoresins), in ICAR AIEEA-PG Code 18 Unit III (flavouring and pigment technology) and in ICAR AICE 35.a Unit 7. India is the largest producer, consumer and exporter of spices, so Indian syllabi give the topic weight, but the same questions of quality, safety and adulteration arise in every spice-importing country. Standards for spices are set nationally, by ISO, and increasingly through the Codex Committee on Spices and Culinary Herbs; the values differ between them, and this manual says so where it matters.
Every spice owes its use to a small set of compounds. The volatile (essential) oil, usually a few per cent of the dry spice or less, carries the aroma; it is made mainly of terpenes (monoterpenes and sesquiterpenes and their oxygenated derivatives) and phenylpropanoids. The non-volatile fraction carries pungency, bitterness and colour. Pungent principles are not volatile and are not tasted as aroma; they act on heat and pain receptors in the mouth. Fixed oil, protein, fibre, starch and minerals make up the bulk of the spice and matter for processing but not for flavour.
Composition varies widely with variety, growing region, maturity at harvest, curing, drying and storage. For that reason this manual gives the identity of the key compounds, which is textbook fact, and treats percentages as ranges that differ between sources and trade grades. A buyer specifies the content that matters, for example volatile oil for cardamom, piperine for pepper, curcumin for turmeric or colour value for paprika, and pays for it. Storage losses come from evaporation of volatiles, oxidation of terpenes, and light-induced fading of pigments, so whole spices keep better than ground spices, and ground spices keep better cold, dry and dark.
Black pepper (Piper nigrum), called the king of spices, is the dried, unripe fruit. Its pungency comes from the alkaloid piperine and related amides; its aroma comes from a volatile oil rich in monoterpenes such as pinenes, sabinene and limonene and the sesquiterpene caryophyllene. White pepper is the seed after the outer pericarp has been removed, traditionally by soaking ripe berries in water (retting) and rubbing; it is less aromatic but valued in light-coloured foods. Green pepper is harvested immature and preserved in brine or dried quickly to keep its colour.
Chilli (Capsicum species) gets its pungency from capsaicinoids, chiefly capsaicin and dihydrocapsaicin, and its red colour from carotenoids, chiefly capsanthin and capsorubin. Pungency is expressed in Scoville heat units (SHU); paprika types are low in pungency and bred for colour. Turmeric (Curcuma longa) is a rhizome whose yellow colour comes from curcuminoids (curcumin, demethoxycurcumin and bisdemethoxycurcumin) and whose aroma comes from turmerones in the volatile oil. Ginger (Zingiber officinale) owes its pungency in the fresh rhizome to gingerols; on drying, heating and storage gingerols dehydrate to shogaols, which are more pungent, and its aroma comes from sesquiterpenes such as zingiberene.
Small cardamom (Elettaria cardamomum), the queen of spices, is valued for its volatile oil, in which 1,8-cineole and α-terpinyl acetate dominate; the green colour of the capsule is a quality attribute and is kept by careful drying. Clove (Syzygium aromaticum) is the dried flower bud; its oil is mostly eugenol. Cinnamon (Cinnamomum verum) and cassia (Cinnamomum cassia and related species) are barks whose oil is dominated by cinnamaldehyde; cinnamon leaf oil, in contrast, is rich in eugenol. Cassia contains much more coumarin than true cinnamon, which matters for safety. Nutmeg and mace come from the same fruit of Myristica fragrans: nutmeg is the seed and mace the red aril around it; both contain myristicin.
Saffron (Crocus sativus) is the dried stigma; its colour comes from crocin, its bitter taste from picrocrocin and its aroma from safranal, formed from picrocrocin during drying. Vanilla (Vanilla planifolia) develops its flavour only during curing, when glucovanillin in the green bean is hydrolysed by β-glucosidase to free vanillin. Cumin owes its aroma to cuminaldehyde, coriander seed to linalool, fennel and star anise to anethole, and mint to menthol. Mustard and garlic have no strong aroma until the tissue is damaged: in mustard the enzyme myrosinase converts sinigrin to allyl isothiocyanate, and in garlic alliinase converts alliin to allicin.
Most spices are dried soon after harvest to a moisture content low enough to stop mould growth and enzyme action; safe moisture levels differ between spices and standards, and are commonly around 10–12% or below for whole dried spices. Sun drying on clean surfaces is still the most common method for pepper, chilli, turmeric and ginger in producing countries, but it exposes the produce to dust, birds, insects and rain. Mechanical driers and solar driers give faster, cleaner and more uniform drying.
Several spices need a curing step before drying. Pepper berries are often dipped in hot water for a minute or so before drying; this cleans them, speeds and evens drying, and gives a uniform black colour by promoting browning of the skin. Turmeric rhizomes are boiled or steamed in water until soft, which gelatinises starch, spreads the colour evenly and kills the rhizome, then dried and polished to remove the rough skin. Ginger is peeled or scraped and dried; bleached ginger was traditionally treated with lime. Cardamom capsules are dried at moderate temperature in curing houses to keep their green colour. Vanilla beans are killed by heat, sweated, slowly dried and conditioned over weeks so that enzymes release vanillin. The yield of dried spice follows from a solids balance: dry mass = fresh mass × (1 − initial moisture) ÷ (1 − final moisture).
Dried spices arrive with stones, soil, stems, chaff, light and immature berries, insect fragments, animal excreta and metal. Cleaning lines use sieves and aspirators to separate by size and density, destoners, gravity tables, magnets and metal detectors, and optical colour sorters to reject discoloured or mouldy units. Grading follows by size, density and colour; for pepper, bulk density (litre weight) is a traditional grade attribute, because light berries are immature or hollow. Cleanliness specifications set limits on extraneous matter, insect damage, mould and excreta; limits differ between national standards, ISO standards and the specifications used by importing trade associations, so a processor works to the buyer's specification and the destination's law.
Spices are hygroscopic and absorb water and odours. Clean, dry, cool, dark storage in moisture-proof bags or containers, protection from storage insects, and stock rotation preserve quality. Fumigation of stored spices is regulated and some fumigants are banned in particular markets.
Grinding increases surface area and releases flavour but also exposes volatile oil to evaporation and oxygen. Conventional mills (hammer, pin, plate and attrition mills) heat the product by friction; the temperature rise drives off volatiles, oxidises them, and in oily spices such as nutmeg, clove and pepper causes the ground material to smear and clog the mill. Cooling the mill, reducing throughput or grinding at low temperature limits these losses; cryogenic grinding is treated in its own chapter. Particle size is specified by sieve analysis; very fine powders release flavour fast but lose it fast in storage. Mill design and size-reduction laws are in mechanical-unit-operations.
Because they are dried in the open, spices often carry high counts of bacteria and moulds, including spore-formers and sometimes Salmonella, and they can carry mycotoxins such as aflatoxins and ochratoxin A from mould growth before or during drying. Microbial reduction methods include steam treatment (saturated or superheated steam for a short time, followed by drying and cooling), which is widely used; ionising radiation, permitted for spices in many countries under the general rules for irradiated food and requiring labelling; and fumigation with ethylene oxide, which is effective but leaves residues and is banned or tightly restricted in many markets. Microbial reduction does not destroy mycotoxins already formed, so prevention by fast, clean drying and dry storage is essential. Toxicology of mycotoxins is in food-toxicology-contaminants-allergens.
In a conventional mill most of the energy put into the spice ends as heat. The product temperature can rise high enough to evaporate a significant part of the volatile oil, to oxidise the oil that remains, and to melt or soften fat in oily spices so that particles stick to the mill surfaces and screens. Cryogenic grinding prevents this by cooling the spice, usually with liquid nitrogen at about −196 °C, before and during grinding. The cold makes the spice brittle, so it fractures cleanly into fine particles with less energy; the fat stays solid, so the mill does not clog; and the nitrogen vapour forms an inert, oxygen-poor atmosphere that limits oxidation. Volatile oil retention, colour and flavour of cryo-ground spices are reported to be better than those of conventionally ground spices, and the powder is finer and more uniform.
The main drawback is cost: liquid nitrogen is consumed in large amounts and the plant needs insulated equipment, safe handling of a cryogenic liquid, and ventilation, because nitrogen displaces oxygen and can asphyxiate workers in a closed room. Cold ground powder must also be protected from condensation of moisture from the air as it warms.
A typical line has a feed hopper, a precooler, usually a screw conveyor in which liquid nitrogen is sprayed directly onto the spice or circulated in a jacket, a mill (often a pin, hammer or turbo mill) that is itself cooled, a sieve, and a cyclone or filter to separate the powder from the gas. The degree of cooling is set by the spice and the target: a spice needs to be cooled below the temperature at which its fat and oil become brittle and non-sticky, which differs between spices, and over-cooling only wastes nitrogen. Nitrogen consumption is expressed per kilogram of product and depends on the feed temperature, the target temperature, the heat generated in grinding and the losses of the equipment.
Alternatives with lower running costs include grinding with chilled air or water-jacketed mills, which reduce but do not prevent heating, and grinding with carbon dioxide snow. Cryogenic grinding is used most for high-value, oil-rich spices such as nutmeg, clove, cardamom, black pepper and cinnamon, and for products where colour and aroma retention justify the cost. Research groups in India and elsewhere have published comparisons of volatile oil retention for many spices, and the results consistently favour low-temperature grinding, although the size of the gain differs with spice and mill.
An essential oil is the volatile, odorous fraction of a plant, obtained by distillation with water or steam, by mechanical expression (for citrus peels) or by dry distillation. Essential oils are mixtures of dozens to hundreds of compounds, mostly terpenes, sesquiterpenes, their oxygenated derivatives (alcohols, aldehydes, ketones, esters, oxides) and phenylpropanoids such as eugenol and anethole. The oxygenated compounds usually carry most of the characteristic odour, while the hydrocarbon terpenes, which oxidise easily and dissolve poorly in water and dilute alcohol, contribute less to flavour and much to instability. Folded or deterpenated oils have had part of the terpene hydrocarbons removed by vacuum distillation, solvent partition or chromatography, which concentrates the flavour and improves solubility and stability; citrus oils are commonly treated this way.
Essential oils are used to flavour soft drinks, confectionery, baked goods, sauces and meat products, and in perfumery and pharmaceuticals. Their content in a spice is measured in the laboratory by hydrodistillation in a Clevenger-type apparatus and reported as millilitres of oil per 100 g of material (% v/w); multiplying by the oil's density gives % w/w.
Three distillation methods are used. In hydrodistillation (water distillation) the plant material is immersed in boiling water; it suits flowers and powders that would clump in steam but risks overheating and hydrolysis. In water-and-steam distillation the material sits on a grid above boiling water. In direct steam distillation, steam from a separate boiler is passed up through the packed material; it is the main industrial method because it is faster, more controllable and suits large batches. The vapour of water and oil is condensed and the oil separates from the water in a separator (Florentine flask) because the two are immiscible; oil lighter than water collects at the top and heavier oils, such as clove oil, at the bottom.
Steam distillation works at temperatures below 100 °C at atmospheric pressure because two immiscible liquids each exert their own vapour pressure independently. The mixture boils when the sum of the two vapour pressures equals the external pressure, so high-boiling oil components distil at a temperature just under the boiling point of water, without decomposition. The mass ratio of oil to water in the distillate equals the ratio of the products of each component's vapour pressure and molar mass: m_oil ÷ m_water = (P_oil × M_oil) ÷ (P_water × M_water). Because the oil's vapour pressure is small, much water is needed per kilogram of oil, but its higher molar mass partly compensates. Distillation time, steam rate, particle size and packing density determine yield and quality; comminuting the material before distillation raises yield, but volatiles are lost if it then waits in the open.
Citrus peel oils are recovered by cold pressing (expression), because distillation would damage their delicate aldehydes; the oil is released from the peel oil glands by rasping or pressing and separated from the aqueous emulsion by centrifuge. Flowers whose aroma would be destroyed by heat, such as jasmine, are extracted with a volatile solvent such as hexane to give a waxy concrete, which is then washed with ethanol, chilled to remove waxes and stripped of ethanol to give an absolute. Enfleurage, absorbing flower scent into cold fat, is a historical method. Supercritical carbon dioxide extraction, discussed under oleoresins, gives oils and extracts close to the natural aroma and free of solvent residues. Microwave-assisted and ultrasound-assisted extraction speed up hydrodistillation and solvent extraction and are the subject of much research.
Essential oils are stored full, cold and dark, in containers of glass, aluminium or lined steel, often under nitrogen, because terpenes oxidise to off-flavoured and in some cases skin-sensitising products. Quality is assessed by gas chromatography for composition, and by physical constants such as specific gravity, refractive index, optical rotation and solubility in alcohol. These constants are specified in ISO standards and pharmacopoeias for each oil and are used to detect adulteration, for example with cheaper oils or synthetic substances; methods are in food-analysis.
An oleoresin is the concentrated extract of a spice obtained with a volatile solvent, which is then removed. It contains the whole flavour of the spice: the volatile oil, the non-volatile pungent principles, pigments, resins and some fixed oil. Black pepper oleoresin carries piperine and pepper oil; capsicum oleoresin carries capsaicinoids; paprika oleoresin carries capsanthin and capsorubin; turmeric oleoresin carries curcuminoids and turmeric oil; ginger oleoresin carries gingerols and ginger oil. Oleoresins are viscous liquids or pastes.
Food manufacturers prefer oleoresins to ground spice for several reasons. Their strength can be standardised by blending, so every batch of a sauce or snack seasoning tastes the same. They are free of the microbial load, dirt, filth and insect fragments that ground spices can carry. They are compact to store and ship, they do not show specks in a clear sauce, and they release flavour evenly. Their drawbacks are that they lack the fibre and visual character of ground spice, are sticky and hard to weigh in small amounts, and can lose their most volatile notes during solvent removal. They are therefore often plated on salt or dextrose (dry soluble spices), emulsified with permitted emulsifiers to disperse in water, or encapsulated.
In solvent extraction, the dried spice is ground to a suitable particle size, packed in extractors and percolated with solvent at or slightly above room temperature until the flavour is exhausted. The solvent is chosen for the compounds to be extracted, its selectivity and the residues permitted: acetone, ethanol, ethyl acetate, hexane and some chlorinated solvents have been used, and permitted solvents and their residue limits are set by each country's regulations. The miscella (extract in solvent) is filtered and the solvent is removed by distillation, first at atmospheric pressure and then under vacuum, with care to keep the temperature low and to recover the volatile oil that distils with the last of the solvent. Some processes first steam-distil the volatile oil, extract the spent spice with solvent for the non-volatile fraction, and then blend the two.
Yield of oleoresin is the mass of oleoresin per mass of spice, reported as a percentage; it depends on the spice, its quality, particle size, solvent and the number of extraction stages. The strength of an oleoresin is expressed by the content of its key compound, for example piperine or capsaicin, or by its colour value. A rough guide to how much ground spice an oleoresin replaces follows from yield: if a spice gives 10% oleoresin, one kilogram of oleoresin carries the extractable flavour of about ten kilograms of that spice, although in practice the replacement is set by sensory and chemical comparison.
A supercritical fluid is a substance held above its critical temperature and pressure, where it has a density close to that of a liquid and a viscosity and diffusivity close to those of a gas. Carbon dioxide has a critical point at about 31 °C and 7.4 MPa, so it can be used as a supercritical solvent at mild temperatures. Its solvent power rises with density, which the operator controls through pressure and temperature: at lower density it dissolves mainly volatile oil, and at higher density it also dissolves fixed oils, pigments and pungent compounds. Polar compounds dissolve poorly unless a small amount of a co-solvent such as ethanol is added. After extraction the pressure is lowered in separators, the carbon dioxide loses its solvent power, the extract drops out, and the gas is recompressed and recycled.
Supercritical carbon dioxide extracts are free of solvent residues, are obtained without heat damage, and keep the top notes that are lost in conventional desolventisation, so they are close in odour to the fresh spice. Fractional separation in several separators at stepped pressures gives fractions rich in volatile oil or in oleoresin. The process needs expensive high-pressure equipment and is mostly batchwise for solids, so it is used for high-value extracts, and also for decaffeination and hop extraction. Subcritical carbon dioxide (liquid carbon dioxide) is used for the most delicate aromas.
Flavour is the combined perception of taste, sensed on the tongue (sweet, sour, salty, bitter and umami), aroma, sensed by the olfactory epithelium either through the nose or retronasally from the mouth, and chemesthetic sensations such as pungency and cooling. Most of what we call flavour is aroma, carried by volatile compounds present at low concentrations. The importance of an aroma compound depends not on its concentration alone but on its concentration relative to its odour threshold: the odour activity value (OAV), concentration ÷ threshold, shows which compounds actually contribute. A compound present at a few micrograms per kilogram can dominate if its threshold is lower still.
Flavourings are classified in law by their origin. A natural flavouring is obtained from plant, animal or microbial material by physical, enzymatic or microbiological processes. A nature-identical flavouring substance is chemically identical to a substance found in nature but is made by synthesis or isolated by chemical means; this category exists in some legislations, including India's, while the European Union stopped using it in its present flavouring regulation, and the United States groups such substances with artificial flavours. An artificial (synthetic) flavouring substance has not been found in nature, ethyl vanillin being the classic example. The definitions differ between jurisdictions, so the same molecule can be labelled differently in different markets.
Vanilla illustrates the categories. Natural vanilla extract is made from cured vanilla beans; its flavour is vanillin plus many minor compounds that give a rounded taste. Vanillin itself can be produced in several ways: extracted from vanilla beans (natural, and very expensive), synthesised chemically from guaiacol or produced from lignin (in the past a major route), which gives a molecule identical to that in vanilla and is classed as nature-identical or artificial depending on the legislation, or produced by fermentation or bioconversion of natural precursors such as ferulic acid, which may qualify as natural where the law allows. Ethyl vanillin, made only by synthesis, has a stronger vanilla odour than vanillin and is an artificial flavouring substance.
Authenticity testing is therefore an important part of flavour quality control. Isotope ratio analysis (carbon-13 and deuterium ratios measured by mass spectrometry or nuclear magnetic resonance) distinguishes vanillin from vanilla beans, lignin, guaiacol and some fermentation routes, because each source leaves a characteristic isotopic signature. The same principle is used for other natural flavours, such as citral, benzaldehyde and raspberry ketone, that are commonly faked.
A compounded flavour is a blend of flavouring substances and extracts in a solvent or carrier, designed by a flavourist to reproduce or create a flavour, together with permitted solvents such as ethanol, propylene glycol or triacetin, and sometimes emulsifiers and antioxidants. Flavours are supplied as liquids (water-soluble or oil-soluble), emulsions for soft drinks, and powders (spray-dried or plated). Dose rates are low, commonly a fraction of a per cent of the food, and the flavour must be chosen for the processing it will meet: heat, pH, fat content and shelf life all affect which compounds survive.
Flavouring substances are evaluated for safety by expert bodies such as the Joint FAO/WHO Expert Committee on Food Additives and national authorities, and many countries maintain positive lists. Some naturally occurring constituents are restricted because they are toxic at high intake; examples include coumarin, safrole, estragole, methyleugenol, pulegone and thujone, for which maximum levels in foods or bans on adding the isolated substance exist in several jurisdictions. Labelling rules govern the words natural, flavour and flavoured. Safety assessment is in food-toxicology-contaminants-allergens.
Flavour compounds are volatile, oxidise easily and react with other food components. Encapsulation surrounds them with a wall or embeds them in a matrix that slows evaporation, keeps oxygen out, converts a liquid into a free-flowing powder that is easy to handle and dose, and allows controlled release at the right moment, for example on contact with water, on heating, on chewing or in the gut. The terms describe the product: the core (or active) is the flavour; the wall (shell, carrier or matrix) is the protecting material; loading or payload is the fraction of the powder that is flavour; and retention is the fraction of the flavour fed to the process that ends up in the powder. Surface oil, the flavour left on the outside of the particles, oxidises quickly and should be low.
Wall materials are chosen for film-forming ability, emulsifying power, low viscosity at high solids, low cost and the release required. Gum arabic (acacia) is the traditional standard because it both emulsifies and forms a good film; maltodextrins are cheap and give glassy matrices but do not emulsify; chemically modified starches, especially octenyl succinate (OSA) starch, emulsify well and largely replace gum arabic; proteins such as whey and caseinates, and blends of these materials, are also used.
Spray drying is the most widely used method because it is cheap, continuous and uses existing equipment. The flavour is emulsified into a concentrated solution of the wall material, the emulsion is atomised into hot air, and a skin forms rapidly on each droplet; because the skin lets water out faster than the larger flavour molecules, most of the flavour is retained even though the air is hot. Retention improves with high feed solids, a good emulsion with small oil droplets, and appropriate inlet and outlet temperatures. Spray-dried flavours are porous and their shelf life against oxidation is limited. Spray drying principles are in evaporation-dehydration.
Melt extrusion disperses flavour in a molten carbohydrate mass that is extruded and cooled into a dense glass with very low oxygen permeability; extruded flavours have long shelf life, especially for citrus oils, but lower loading. Complex coacervation uses the attraction between a positively charged protein, typically gelatin below its isoelectric point, and a negatively charged polysaccharide such as gum arabic to deposit a continuous shell around oil droplets; it gives high loading and controlled release but is costly. Molecular inclusion in β-cyclodextrin, a ring of seven glucose units with a hydrophobic cavity, protects individual flavour molecules. Fluidised-bed coating, plating on salt or sugar, liposomes and emulsion systems complete the range.
Process (reaction) flavours are made by heating together precursors that react to give the flavours of cooked foods: meaty, roasted, chocolate, caramel, bready and coffee notes. The main chemistry is the Maillard reaction between a reducing sugar and an amino compound, whose general mechanism (Amadori and Heyns rearrangement products and their degradation) is in food-chemistry-major-constituents. For flavour, two branches matter most. Strecker degradation of amino acids by dicarbonyl compounds formed from sugars yields Strecker aldehydes with characteristic odours (for example 3-methylbutanal, malty, from leucine, and methional, cooked potato, from methionine) together with aminoketones that condense into pyrazines, which give roasted and nutty notes. Sulphur-containing amino acids, especially cysteine, react with sugars and their breakdown products to give thiazoles, thiophenes and thiols with meaty and savoury character; heating cysteine with a pentose such as ribose is a classic route to meat flavour. Proline gives bready and roasted notes, including 2-acetyl-1-pyrroline.
The flavour obtained depends on the amino acid and sugar chosen, the ratio, the water content, the pH, the temperature and the time. A manufacturer controls these to give a consistent product, which is then dried or blended into seasonings.
Yeast extracts, made by autolysis or hydrolysis of yeast, supply glutamate, nucleotides and peptides that give savoury taste and serve as precursors in reaction flavours. Hydrolysed vegetable proteins (HVP), made by hydrolysing soy, wheat or maize protein with hydrochloric acid, are strongly savoury, but acid hydrolysis of protein in the presence of residual fat can form chloropropanols such as 3-MCPD, which are regulated contaminants; enzymatic hydrolysis avoids this. Smoke flavourings are made by condensing wood smoke and refining it into liquid smoke; the refining removes much of the polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, for which limits are set, and many smoke flavourings are approved individually. Caramel colours and flavours come from controlled heating of sugars, alone or with reactants.
Because heating sugars with amino acids can also form unwanted compounds, including acrylamide from asparagine and heterocyclic amines at high temperatures, industry guidelines and regulations set conditions for thermal process flavourings, including maximum processing temperatures and times, and some contaminant limits. Codex guidelines describe thermal process flavourings as products obtained by heating precursors under defined conditions, and many countries regulate them as a distinct category.
Colour is the first quality a consumer judges, and the food industry uses both synthetic colours and colours from natural sources. Synthetic colours, such as tartrazine and sunset yellow, are bright, stable and cheap, but consumer demand has shifted many products to natural colours, which are less stable and more expensive. The technology of natural colours is largely the technology of stabilising them.
Carotenoids are fat-soluble yellow, orange and red pigments. Annatto, from the seed coat of Bixa orellana, gives bixin, which is oil-soluble, and norbixin, made by alkaline hydrolysis of bixin, which is water-soluble; annatto colours cheese, butter and snacks. Paprika oleoresin contributes capsanthin and capsorubin and is standardised by colour value. β-Carotene, lutein from marigold and lycopene from tomato are also used. Carotenoids are fairly heat-stable but oxidise with light and oxygen, so they are formulated with antioxidants and supplied as oil solutions, emulsions or water-dispersible beadlets. Curcumin from turmeric gives a bright yellow; it is light-sensitive, nearly insoluble in water, and turns red-brown in alkaline conditions, so it is supplied as oleoresin, as purified curcumin in solvents or emulsions, or encapsulated.
Anthocyanins from grape skins, black carrot, purple sweet potato, red cabbage and berries give red to purple colours that depend strongly on pH: red and most stable in acid, colourless to bluish and less stable as pH rises. They suit acid products such as soft drinks, jams and confectionery; acylated anthocyanins, as in black carrot and red cabbage, are more stable. Betalains, mainly betanin from beetroot, give a red that is stable over a wider pH range than anthocyanins but is destroyed by heat and light, so beetroot red is used in products with mild processing and short or chilled storage, such as yoghurt and ice cream. Chlorophyll gives green but loses magnesium in acid and heat to olive pheophytin; replacing magnesium with copper gives copper chlorophyll and copper chlorophyllin, which are much more stable. Carmine, from carminic acid of the cochineal insect, is a very stable red, but it is of animal origin and an allergen for some people. Spirulina extract supplies the blue phycocyanin, which is sensitive to heat and acid. Caramel colours, made by heating sugars, are classed in four classes by the reactants used (plain, caustic sulphite, ammonia, sulphite ammonia); classes made with ammonia can contain 4-methylimidazole, which is limited by regulation.
Many plant extracts used for colour, such as spirulina or safflower, are classed in some jurisdictions as colouring foods rather than additives if they are concentrated without selective extraction of the pigment; the boundary between the two is drawn differently in different countries.
Many plants used as spices or herbs are also traditional medicines, and the boundary between a culinary herb, a functional ingredient and a herbal medicine is drawn by regulation rather than by the plant. Aromatic plants grown mainly for essential oils include mints (Mentha arvensis for menthol, peppermint and spearmint), lemongrass (citral), palmarosa (geraniol), citronella, vetiver, basil, eucalyptus (1,8-cineole) and rose. Medicinal plants appearing in foods, beverages and supplements include holy basil or tulsi (Ocimum tenuiflorum, rich in eugenol), ashwagandha (Withania somnifera, withanolides), ginseng (ginsenosides), liquorice (glycyrrhizin, intensely sweet), stevia (steviol glycosides, a high-intensity sweetener), fenugreek, moringa leaf, aloe vera, brahmi and garcinia.
Processing follows the same principles as for spices: harvest at the stage of highest active content, careful drying at moderate temperature to keep volatiles, cleaning, grinding and extraction with water, ethanol or supercritical carbon dioxide. Extracts are often standardised to a marker compound, such as a content of withanolides or steviol glycosides, and good agricultural and collection practices are needed to avoid misidentification, contamination and overharvesting of wild plants.
Natural does not mean safe. Some herbs contain compounds that are toxic at high or prolonged intake: pyrrolizidine alkaloids in some borage-family and other plants and as contaminants of herbal teas; coumarin in cassia; glycyrrhizin in liquorice, which raises blood pressure at high intake; estragole and methyleugenol in basil and tarragon; thujone in sage and wormwood; and safrole in sassafras and, in small amounts, in nutmeg. Some herbal ingredients interact with medicines; St John's wort is the best-known example. Herbal products are also vulnerable to adulteration with cheaper plants, to contamination with heavy metals and pesticides, and in supplements to deliberate adulteration with undeclared drugs.
Regulation differs widely. In India, foods containing herbs and botanicals are governed by FSSAI regulations on health supplements, nutraceuticals and foods for special purposes, which list permitted plants and parts, while traditional medicines are regulated separately under the AYUSH system. The European Union treats many botanicals under food law, with novel food rules for plants not consumed before 1997 and restrictions on certain substances, while the United States regulates most as dietary supplements. Claims of health benefit are tightly controlled almost everywhere and must be authorised for the specific ingredient and amount. A food technologist working with botanicals must therefore check the permitted list and the claim rules of each market.
Spice quality is defined by physical, chemical and microbiological attributes. Physical attributes include extraneous matter, light berries and broken pieces, insect damage, mould, excreta, bulk density and particle size. Chemical attributes include moisture, total ash, acid-insoluble ash (a measure of sand and soil), volatile oil, non-volatile ether extract, crude fibre, and the content of the key compound (piperine, capsaicinoids, curcuminoids, colour value). Microbiological attributes include total plate count, yeasts and moulds, coliforms and Salmonella, and contaminants include mycotoxins, pesticide residues, heavy metals, illegal dyes and fumigant residues.
Standards exist at several levels. ISO standards specify many spices; national standards (in India, FSSAI regulations and BIS standards, with the voluntary AGMARK grading for many spices) set legal minimums; importing countries and trade associations publish cleanliness specifications; and the Codex Committee on Spices and Culinary Herbs, chaired by India, has been developing worldwide standards. Limits differ between these documents, so a processor works to the strictest that applies to the market. Moisture in spices is determined by toluene distillation (Dean and Stark method) rather than oven drying, because oven drying also drives off volatile oil and overstates moisture. Detailed methods are in food-analysis.
Spices are high-value and are often sold ground, which makes adulteration tempting and hard to see. Classic examples taught in Indian courses and used in FSSAI's simple detection tests include: dried papaya seeds mixed with black pepper, which float in alcohol while sound pepper sinks; light berries and exhausted pepper from which the oil has been extracted; brick powder, sand or soil in chilli powder, which settle quickly when the powder is stirred in water, and show up as high acid-insoluble ash; artificial and banned dyes, such as Sudan dyes in chilli and metanil yellow in turmeric, the latter giving a pink-violet colour with hydrochloric acid that persists on dilution with water, whereas the violet colour of pure turmeric fades; lead chromate in turmeric to brighten colour; starch added to ground spices, revealed by a blue colour with iodine; coloured stigmas of other flowers, maize silk or dyed threads passed off as saffron, which release colour quickly in water, unlike genuine saffron, which colours water slowly; and soapstone, chalk or resin in asafoetida.
Confirmatory analysis uses microscopy for foreign plant tissue, instrumental methods such as high-performance liquid chromatography for dyes and key compounds, gas chromatography for essential oils, atomic absorption or ICP for lead and other metals, and DNA-based methods for species identification. Several major recalls in international trade have been triggered by illegal dyes in chilli and by ethylene oxide residues, which is why exporters test before shipment.
Pungency of chilli was originally measured by the Scoville organoleptic test, in which an alcohol extract is diluted in sweetened water until a panel can no longer detect heat; the dilution factor is the Scoville heat unit value. The method is subjective and has been replaced by high-performance liquid chromatography of capsaicinoids, whose result is converted to Scoville heat units by multiplying the capsaicinoid content in parts per million by a conversion factor; a factor of about 16 is used for capsaicin and dihydrocapsaicin, based on pure capsaicin being about 16 million SHU. Mild paprikas measure a few hundred SHU and hot chillies tens of thousands or more. Piperine in pepper is measured by ultraviolet spectrophotometry or HPLC and reported as a percentage.
Colour value of paprika and capsicum oleoresin is measured spectrophotometrically on an acetone extract and reported in ASTA colour units or as an extractable colour value; oleoresins are diluted with vegetable oil to a standard colour value, and since colour value is proportional to concentration, diluting an oleoresin with an equal mass of oil halves its colour value. Turmeric quality is reported as curcuminoid content, measured spectrophotometrically or by HPLC.
A student uses this subject to name the active principle of every major spice, explain why essential oils distil below 100 °C, contrast essential oils with oleoresins, and describe cryogenic grinding, encapsulation and the main natural colours. In the laboratory the same student runs a Clevenger distillation and reports volatile oil as % v/w, measures moisture by toluene distillation, ash and acid-insoluble ash, and performs the simple adulteration tests for pepper, chilli, turmeric and saffron. The numerical questions are mass balances: drying yield, oil and oleoresin yield, dilution of colour value and conversion of capsaicinoid content to Scoville units.
Five years into a spice processing, extraction or seasoning company, a technologist writes raw-material specifications, approves suppliers, and runs the cleaning, steam sterilisation and grinding lines to meet a buyer's microbial and cleanliness limits. In an extraction plant the same person sets particle size, solvent ratio and desolventisation conditions to hit oleoresin yield and strength, standardises batches by blending, and checks residual solvent. A flavour applications technologist chooses encapsulated or liquid flavours for a product's process and shelf life. Each role includes investigating complaints such as weak flavour, specks, colour fading or a failed export test.
After twenty-five years a senior manager decides on capital and markets: whether to invest in cryogenic grinding, steam sterilisation or supercritical CO2 extraction; how to secure traceable supply from many small growers; how to meet each importing country's limits for pesticide residues, mycotoxins, ethylene oxide and illegal dyes; and how to respond when a shipment is rejected or recalled. The same person sets the company's policy on natural claims and labelling across markets, and negotiates specifications with major food manufacturers whose own standards are often stricter than the law.
A researcher with long industry experience works on the science that limits the trade: extraction selectivity and modelling for essential oils and oleoresins, supercritical and subcritical processes, the chemistry of flavour formation and degradation, encapsulation materials that release flavour on demand, isotope and DNA methods for authenticity, decontamination methods that kill pathogens without losing volatiles, and the safety assessment of botanical constituents. Such work supplies the data that standard-setting bodies, including the Codex spice committee, use to set limits and methods.
This manual names the active principles of spices and their behaviour but gives composition only as ranges or not at all, because contents vary with variety, origin and processing; it does not reproduce national, ISO or trade-association limits for each spice, which differ and change. It gives no permitted solvent residue limits, irradiation doses, fumigant limits or maximum levels of restricted flavour constituents, which must be read from the current regulation of each market. Equipment design for mills, distillation units and supercritical extractors is outlined only. Cocoa, coffee and tea, also plantation crops, are in beverage-technology and sugar-confectionery-chocolate; the general chemistry of the Maillard reaction is in food-chemistry-major-constituents; analytical methods in full are in food-analysis.
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. Compositions and limits for spices differ by variety, origin and country; questions avoid quoting national limits.
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