Dairy Science & Technology · Dairy Processing & Product Technology · also By-products Technology, Whey Processing
Turning whey, buttermilk, ghee residue and permeates into ingredients, beverages and energy instead of waste.
In the exams: ICAR AICE subject 37 Units 1 and 4; ICAR AIEEA-PG group 17 Unit I
Whey and other dairy by-products used to be called waste. Whey, in particular, was fed to pigs, spread on fields or poured into rivers, with severe pollution. Today it is the raw material for a large industry: whey powders, demineralised whey for infant formula, whey protein concentrates and isolates for sports and clinical nutrition, lactose for food and pharmaceuticals, lactose derivatives such as galacto-oligosaccharides, permeate powders, beverages, whey cheeses, ethanol and biogas. Buttermilk and ghee residue, once losses, are now sources of emulsifiers, antioxidants and food ingredients.
This manual covers the types and composition of whey; the disposal problem measured as BOD and COD; whey beverages and whey cheeses; whey powder and demineralised whey; whey protein concentrates and isolates; lactose manufacture and refining; casein, caseinates and co-precipitates; buttermilk and its phospholipids; ghee residue; permeate; and fermentation of whey to ethanol, biogas and single-cell protein. Membrane processes are covered in depth in membrane-processing-dairy-ingredients, drying in evaporation-drying-dairy and concentrated-dried-milks, butter and ghee in fat-rich-dairy-products, and effluent treatment in dairy-effluent-environment; this manual refers to them.
ICAR AICE-JRF/SRF Dairy Technology (subject 37) includes dairy by-products in Unit 1 and, in Unit 4, preparation of lactose, low-lactose powders, whey protein concentrates, casein and co-precipitates, demineralisation and the functional properties of whey proteins; ICAR AIEEA-PG Dairy Technology includes manufacture of dairy products and membrane processing. Values for composition, BOD and yields are representative; plant data and national rules must be used in practice.
Whey is the liquid that remains after casein and fat have been removed from milk as curd. Every kilogram of cheese leaves roughly nine kilograms of whey, so cheese-making regions produce whey in vast quantities, and paneer, chhana, cottage cheese, quark, strained yoghurt and casein manufacture add more. Whey is classed by how the curd was formed. Sweet whey comes from rennet-coagulated cheeses such as Cheddar, Gouda, Mozzarella and Swiss types; its pH is close to that of milk, commonly about 6.0–6.6. Acid whey comes from acid-coagulated products — acid casein, cottage cheese, quark, cream cheese, strained yoghurt, paneer and chhana — and has a pH around 4.5–5.0 (somewhat higher for heat-acid products such as paneer); it contains more lactic acid, more calcium and phosphate dissolved from the casein micelles during acidification, and is harder to process. The terms 'cheese whey', 'casein whey' and 'Greek yoghurt acid whey' are also used.
Whey contains about half of the solids of milk, but in a very dilute form: typically around 6–7 per cent total solids and 93–94 per cent water. Lactose is the main solid, about 4.5–5 per cent of the whey (around three-quarters of its solids). Proteins make up about 0.6–0.8 per cent; the main whey proteins are beta-lactoglobulin (roughly half of whey protein), alpha-lactalbumin (roughly a fifth), bovine serum albumin, immunoglobulins, lactoferrin, lactoperoxidase and proteose-peptones; sweet whey also contains the caseinomacropeptide released by chymosin, which makes up a considerable fraction of its protein. Minerals (ash) make up about 0.5–0.8 per cent, higher in acid whey; there is a little residual fat (higher in whey from high-fat cheese and before separation), lactic acid (much more in acid whey), water-soluble vitamins (whey is naturally greenish-yellow from riboflavin), and non-protein nitrogen. Exact values vary with the milk, the cheese variety and the process.
Because whey carries most of the milk's lactose and whey protein, it is both a pollution problem and a valuable raw material. The whole of this subject is about turning it, and other dairy side streams, into products: beverages and whey cheeses, powders, protein concentrates, lactose and its derivatives, and energy.
The value of whey depends heavily on how it is handled in the first hours. Fresh sweet whey is warm, contains live starter bacteria and residual coagulant, and continues to ferment: lactose turns to lactic acid, pH falls and the whey becomes progressively less suitable for high-value products. Good practice is to separate curd fines (by screens, vibrating sieves or clarifiers, returning fines to the cheese where possible), separate residual fat as whey cream (used in butter, whey cream or returned to cheese milk), then either cool the whey quickly to below about 7 °C or pasteurise it, and process it within a short time. Whey from different cheese varieties (salted or unsalted, sweet or acid, with or without colour such as annatto in Cheddar whey) must be kept apart according to its intended use; annatto must be bleached or removed for some protein products. Small cheese plants that cannot process whey themselves often sell it to central whey processors, which requires collection logistics and quality agreements.
Whey has one of the highest pollution loads of any food-industry effluent. Its organic matter, mostly lactose with protein and lactic acid, is rapidly consumed by micro-organisms that use up dissolved oxygen. Biochemical oxygen demand (BOD, the oxygen used by micro-organisms in degrading organic matter over a standard period, usually five days at 20 °C) is commonly quoted at around 30,000–50,000 mg/L for whey, and chemical oxygen demand (COD, the oxygen equivalent of the organic matter oxidised by a strong chemical oxidant) at around 60,000–80,000 mg/L, compared with a few hundred mg/L BOD for domestic sewage. Discharged into rivers, whey depletes oxygen and kills fish; spread on land in excess, it damages soil structure, salinises soils (especially acid whey, which is rich in minerals) and can contaminate groundwater; added to municipal sewage works, it overloads treatment capacity. Lactose contributes most of the BOD, so removing protein alone (as in protein concentration) still leaves a permeate with a high BOD.
Pollution loads are calculated by multiplying volume by concentration. A plant producing 100,000 litres of whey a day with a BOD of 40,000 mg/L (40 g/L) discharges 4,000 kg of BOD per day. Population equivalent compares this with the load from people: taking, for example, 60 g BOD per person per day (a value commonly used in Europe and India; some countries use slightly different figures), 4,000 kg of BOD equals the daily load of about 66,700 people. COD loads are calculated in the same way and are used for anaerobic treatment design, since methane yield is linked to COD removed. Regulations set discharge limits for BOD, COD, suspended solids, pH and nutrients, and most countries now prohibit discharge of untreated whey. The practical conclusion is that whey must be used as a raw material, fed to animals under controlled conditions, or treated biologically (often anaerobically with energy recovery) — never simply dumped. Treatment of dairy effluent as a whole is covered in dairy-effluent-environment.
The traditional outlets for whey — liquid feed for pigs and cattle, and spreading on farmland — remain important for small plants, but both need control. Pigs and cattle can use liquid whey as a source of energy and protein, but intake must be introduced gradually and balanced with other feed, salt content must be considered, and whey must be fresh to avoid digestive upsets; acid whey is less suitable. Land application is permitted in some places under strict limits on application rate, soil type, distance from water courses and timing, because excessive application causes anaerobic soils, odours, salinisation and nitrate and phosphate run-off. These outlets have low value, and as regulations tighten and volumes grow, they are being replaced by processing or anaerobic digestion.
Whey can be made into drinks, which is one of the simplest ways to use it on a small scale. Plain or flavoured whey drinks are made from sweet or paneer whey, clarified (sometimes deproteinised by heat to prevent sediment), blended with sugar, fruit juice or pulp, flavours and stabilisers, then pasteurised or UHT-treated. Fermented whey beverages use lactic cultures (sometimes probiotic) to give a tangy drink; carbonated whey drinks are popular in some European countries; and alcoholic beverages such as whey wine, whey beer and distilled spirits are made by fermenting lactose with lactose-fermenting yeasts (see the fermentation chapter). In India, beverages from paneer and chhana whey, often with fruit, mint or spices, are produced by dairies and research institutes. Whey drinks retain whey proteins, lactose, minerals and B vitamins and are marketed for refreshment and sports recovery; their technical problems are protein sedimentation on heating, whey flavour (which needs masking), and microbial stability.
Whey proteins, unlike casein, do not coagulate with rennet, but they do coagulate when heated, especially with a little acid and salt. Ricotta (Italian, meaning 'recooked') is made by heating sweet whey, often with some added milk or cream to raise yield and richness, to around 80–90 °C, with acid (citric, lactic or acid whey) and sometimes salt, so that denatured whey proteins aggregate and rise to the surface as fine white curds (floccules), which are skimmed off and drained. Yield from whey alone is low, because whey contains well under one per cent protein. Fresh ricotta is moist, soft and perishable; ricotta salata is salted, pressed and dried. Similar whey cheeses include Greek myzithra and anthotyros, Spanish requesón, Corsican brocciu (a protected designation) and Portuguese requeijão. Paneer whey and chhana whey in India are sometimes used to make ricotta-like products.
Scandinavian brown whey cheese (mysost or brunost, including gjetost made with goat milk) is produced not by coagulation but by evaporation: whey, often with added cream or milk, is boiled down in open kettles or vacuum pans until most of the water has gone and the lactose caramelises and undergoes Maillard browning, giving a brown, fudge-like, sweet product. The concentrate is cooled with stirring to control lactose crystallisation (fine crystals give a smooth texture, coarse ones sandiness), then moulded into blocks. A softer, spreadable version (prim or messmør) is also made. Brown cheese is unusual in that it uses all the solids of whey, including lactose, rather than only the protein. Its yield is calculated from a solids balance: product mass = whey solids (plus added dairy solids) ÷ product total-solids fraction.
Ricotta yield and texture depend on the protein content of the whey, the amount of milk or cream added, the final temperature, the acid used and the pH at coagulation, and on gentle handling of the floccules so that they are not broken. Whey from cheese made with high-heat milk or from long-held whey gives lower yields, because some protein has already been lost or degraded. The heating must be fast enough to form floccules that rise but not so violent that they are dispersed; plants use direct steam injection or jacketed vats, and continuous ricotta systems use tubular heaters and flocculation tubes. For whey drinks, plants choose between keeping the whey proteins (for nutrition, with stabilisers or pH adjustment to prevent sediment) and removing them by heat precipitation and separation (for clear beverages). Mild acidification, homogenisation and pectin stabilisation help keep protein suspended in acidic fruit drinks, as in drinking yoghurts. Whey drinks must be heat-treated adequately because whey is an excellent growth medium.
Drying whey is the most direct way to turn it into a stable, tradable ingredient. Sweet whey is clarified and separated to remove curd fines and fat, pasteurised, and concentrated, often first by reverse osmosis or nanofiltration (which remove water cheaply) and then in a multiple-effect evaporator, to around 50–60 per cent total solids. Because amorphous lactose makes whey powder sticky and hygroscopic, the concentrate is pre-crystallised: it is cooled with slow stirring and sometimes seeded with fine lactose so that most lactose crystallises as alpha-lactose monohydrate before drying. The crystallised concentrate is then spray-dried, usually in a two- or three-stage dryer with a fluid bed for final drying and further crystallisation, giving 'non-caking' whey powder. Acid whey is more difficult to dry because lactic acid and its high mineral content make the powder sticky; it is often neutralised or partly demineralised first, or processed by other routes. Whey powder is used in bakery, confectionery, processed foods, snack seasonings, feed (especially for young animals) and as a raw material for further processing. Drying engineering is covered in evaporation-drying-dairy and powder science in concentrated-dried-milks.
For infant formula and some foods, the high mineral content of whey (with a salty taste and a mineral balance unsuitable for babies) must be reduced. Demineralised whey is named by the percentage of minerals removed: D40 or D50 whey has about 40–50 per cent of its ash removed, and D70 and D90 have about 70 and 90 per cent removed. Nanofiltration removes monovalent ions (sodium, potassium, chloride) and water while retaining lactose and protein, and is used for partial demineralisation to around 30–50 per cent. Electrodialysis uses ion-selective membranes in an electric field to remove ions from the whey stream and can reach higher levels. Ion exchange, using cation and anion exchange resins, reaches the highest levels, often combined with electrodialysis for D90. Demineralised whey powder, particularly D90, is a major ingredient in infant formula, where it supplies lactose and whey protein in a ratio closer to human milk. Ash content after demineralisation is calculated on a dry basis: removing half the ash of a whey with 8 per cent ash in its solids leaves 4 parts ash in 96 parts solids, about 4.2 per cent.
Whey powders are specified for moisture, protein, lactose, ash, fat, pH or titratable acidity, colour, solubility, bulk density, scorched particles and microbiological quality. Heat damage during concentration and drying denatures whey protein and promotes Maillard browning, which lowers solubility, darkens colour and reduces available lysine; it is limited by moderate evaporation and drying temperatures and by quick processing. Caking during storage results from insufficient lactose crystallisation before drying or from moisture uptake, and is prevented by good pre-crystallisation, adequate fluid-bed treatment and moisture-proof packaging. Whey powders from different cheese types differ in salt and acidity, which matters to users; for example, whey from salted curd (as in Cheddar mills) is saltier.
Whey proteins are the most valuable component of whey. Whey protein concentrates (WPC) are made by ultrafiltration (UF), which retains proteins while lactose, minerals and water pass into the permeate. As the volume concentration factor rises, the protein content of the retentate increases on a dry-matter basis, because protein is concentrated while lactose and minerals stay at about the same concentration in the liquid. For higher protein contents, diafiltration is added: water is added to the retentate and removed again through the membrane, washing out more lactose and minerals. Products are named by their protein content in the dry matter: WPC 34 (used as a skim milk powder replacer), WPC 35, WPC 50, WPC 60 and WPC 80 are common grades. Whey protein isolate (WPI), with at least 90 per cent protein on a dry basis, is made either by microfiltration and UF with extensive diafiltration, which also removes residual fat, or by ion-exchange adsorption of the proteins followed by elution and UF. Clarification and microfiltration before UF remove fat and phospholipids that otherwise lower protein content and cause off-flavours.
Consider whey with 6.5 per cent total solids, of which 0.6 per cent is protein and 5.9 per cent is lactose, minerals and other small solutes. Suppose UF retains all the protein and lets the small solutes pass freely, so that their concentration in the retentate stays at 5.9 per cent. At a volume concentration factor of 20, the retentate protein is 0.6 × 20 = 12 per cent, its total solids 12 + 5.9 = 17.9 per cent, and the protein in dry matter 12 ÷ 17.9 = 67 per cent, compared with 0.6 ÷ 6.5 = 9.2 per cent in the original whey. Reaching 80 per cent protein in dry matter at practical concentration factors requires diafiltration to wash out the small solutes. Real membranes also retain some non-protein solids and pass some small peptides, so plant figures differ from this idealised calculation.
Whey proteins are valued for nutrition and function. Nutritionally they are rich in essential amino acids, particularly the branched-chain amino acid leucine, and are digested quickly, which underlies their use in sports and clinical nutrition. Functionally they are soluble across a wide pH range when native, gel on heating, foam and emulsify; these properties are exploited in meat products, bakery, beverages, dairy desserts, yoghurt fortification and confectionery. Processing can modify them: heat denaturation and microparticulation give fat-mimetic particles; hydrolysis gives peptides for hypoallergenic infant formula and specialised nutrition. Fractionation separates individual proteins such as alpha-lactalbumin (enriched for infant formula because it is the main whey protein of human milk), lactoferrin, glycomacropeptide (useful for diets for phenylketonuria because it lacks phenylalanine), and immunoglobulins. Each step adds value but also produces permeate streams that must themselves be used.
A whey protein plant is a sequence of membrane and thermal operations. Pre-treatment removes fines and fat by clarification and separation and may include microfiltration to remove residual fat, phospholipids and bacteria, which improves membrane performance and product quality. Ultrafiltration is done with spiral-wound polymeric membranes in most plants, arranged in stages with recirculation loops; diafiltration water is added in later stages. Membrane performance is limited by concentration polarisation (a layer of retained protein builds up near the membrane surface) and fouling (deposition of proteins and calcium phosphate on and in the membrane), both of which reduce flux. Operating temperature (cold operation limits bacterial growth, warm operation gives higher flux), transmembrane pressure and cross-flow velocity are optimised, and membranes are cleaned frequently with alkaline, acid and enzymatic detergents within the membrane's chemical and temperature limits. The retentate is pasteurised, concentrated further by evaporation if needed and spray-dried; permeate goes to lactose, permeate powder or other uses. Membrane principles are treated fully in membrane-processing-dairy-ingredients.
Lactose is made from whey or, increasingly, from the permeate left after protein concentration, which is almost a pure lactose and mineral solution. The feed is concentrated by reverse osmosis and evaporation to a high total solids (commonly around 55–65 per cent), at which lactose is strongly supersaturated when cooled. The concentrate is cooled slowly with gentle stirring in crystallisers over many hours, often with seeding, so that lactose crystallises as alpha-lactose monohydrate; slow cooling gives large, well-formed crystals that separate easily. The crystals are separated from the mother liquor by decanter centrifuges or basket centrifuges, washed with cold water to remove adhering minerals and riboflavin, dried in fluid-bed dryers and milled and sieved to grades of different particle size. Yields depend on how much lactose crystallises, which is limited by its solubility in the mother liquor and by impurities; typically a good fraction of the lactose is recovered as crystals, and the mother liquor (delactosed permeate), rich in minerals and remaining lactose, is used in feed or other products. Because the crystals are a monohydrate, the mass of crystalline product is greater than the anhydrous lactose recovered by a factor of 360 ÷ 342.
Pharmaceutical-grade lactose, used as a filler and excipient in tablets and dry-powder inhalers, is made by redissolving edible lactose, treating the solution with activated carbon to remove colour and impurities, filtering it, recrystallising and drying it under strict control; spray-dried and anhydrous grades are also produced for direct compression. Lactose can be converted into higher-value derivatives. Galacto-oligosaccharides (GOS) are made by the transgalactosylation activity of beta-galactosidase at high lactose concentration and are used as prebiotics in infant formula. Lactulose, made by alkaline isomerisation of lactose, is used as a laxative and prebiotic. Lactitol (a sugar alcohol made by hydrogenation), lactobionic acid (by oxidation), tagatose and glucose-galactose syrups (by hydrolysis) are other derivatives. Lactose-free dairy products and hydrolysed whey syrups use the same enzyme as GOS production but under conditions that favour hydrolysis.
Lactose exists in two anomeric forms, alpha and beta, which interconvert in solution (mutarotation) to an equilibrium of roughly 40 per cent alpha and 60 per cent beta at room temperature. Below about 93.5 °C the stable crystalline form from aqueous solution is alpha-lactose monohydrate; above it, anhydrous beta-lactose crystallises. Because the solubility of lactose is low and rises steeply with temperature, a hot concentrated solution becomes supersaturated on cooling. Crystals grow from nuclei, and mutarotation of beta to alpha must keep pace with crystal growth, which is one reason lactose crystallisation is slow. Controlled cooling profiles, seeding, agitation and the presence of impurities (minerals, proteins, riboflavin) determine crystal size, shape (typically 'tomahawk' crystals of alpha-monohydrate) and yield. Large crystals are easier to separate and wash; fine crystals are wanted where texture matters, as in sweetened condensed milk. The same principles control lactose crystallisation in whey powder pre-crystallisation, condensed milks and ice cream sandiness.
Although not a whey product, casein manufacture belongs here because it is a major use of skim milk and produces large quantities of acid whey. Acid casein is made by acidifying pasteurised skim milk to the isoelectric point of casein, about pH 4.6, with a mineral acid (hydrochloric or sulphuric acid) or by fermentation with lactic cultures (lactic casein), usually with gentle heating (cooking) to firm the curd. The curd is separated from the whey, washed repeatedly with water to remove lactose, acid and salts, dewatered by decanter or press, dried, milled and graded. Rennet casein is made by coagulating skim milk with rennet, giving a calcium paracaseinate curd with a sweet whey by-product; it is used mainly in cheese analogues and some technical applications. Casein yield is calculated from the casein content of skim milk, the recovery (a little casein is lost as fines and, for rennet casein, as caseinomacropeptide) and the moisture of the dried product.
Acid casein is insoluble in water. Caseinates are made by reacting acid casein curd or dried casein with an alkali to raise the pH to near neutral, giving soluble salts: sodium caseinate (with sodium hydroxide), calcium caseinate (with calcium hydroxide), potassium caseinate, and others. The solution is spray-dried or roller-dried. Sodium caseinate is an excellent emulsifier and is used in coffee whiteners, processed meats, nutritional beverages and many processed foods; calcium caseinate forms colloidal dispersions and is used in nutrition products. Co-precipitates are made by heating skim milk to high temperature (commonly about 90 °C) so that whey proteins denature and associate with casein, then precipitating both together with acid or calcium chloride; this recovers whey proteins along with casein and increases protein yield from milk. Co-precipitates are classed by calcium content (high, medium, low calcium) and used in bakery, processed cheese and nutrition products. Milk protein concentrates made by ultrafiltration of skim milk are now an alternative route to high-protein dairy ingredients without producing whey.
Casein and caseinates are graded on protein content, moisture, ash, fat, free acid, colour, particle size, viscosity of solutions (for caseinates), solubility, and microbiological quality, including spore counts, because many uses involve heat processing. Edible casein must be made under food hygiene conditions; technical casein, once used for glues, paints, plastics (casein plastic buttons) and paper coatings, has largely been replaced by synthetic polymers but survives in some niches. Food uses include processed cheese and cheese analogues (rennet casein), nutritional and sports products (calcium and sodium caseinates, micellar casein), coffee whiteners and creamers (sodium caseinate), meat products (as binder and emulsifier), and bakery. The acid whey from casein manufacture is processed like other acid wheys, into lactose, protein concentrates or biogas, or used as feed.
Sweet-cream buttermilk, the liquid released when cream is churned into butter, is covered from the butter-making side in fat-rich-dairy-products. Here it is considered as a by-product. Its composition resembles skim milk, but it is markedly richer in material from the milk fat globule membrane (MFGM), which is released when the globules are disrupted during churning. MFGM contains polar lipids (phospholipids such as phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, and gangliosides) and membrane proteins (such as butyrophilin and mucins). These components have strong emulsifying properties and are being studied for possible benefits to infant development, gut health and cognition, which has led to MFGM-enriched ingredients for infant formula. Buttermilk from cultured cream is acid and less versatile, and that from ghee or desi butter making in South Asia (chhach) is used as a beverage.
Buttermilk is used fresh in bakery, confectionery and dairy products, or dried to buttermilk powder, which serves as an emulsifier and flavour ingredient in baked goods, chocolate, recombined dairy products, ice cream and dressings. MFGM-rich ingredients are made by concentrating buttermilk (or beta serum from anhydrous milk fat manufacture, which is even richer in polar lipids) by microfiltration and ultrafiltration, sometimes after removing casein by acid or rennet precipitation, and drying the retentate. Because phospholipids are prone to oxidation, buttermilk powders and MFGM ingredients need careful processing and packaging. Fat losses into buttermilk are minimised in butter making for efficiency, but the membrane material in buttermilk is now seen as a valuable co-product rather than a loss.
The value of buttermilk and MFGM ingredients is expressed by their polar lipid and phospholipid contents, measured by methods such as thin-layer or high-performance liquid chromatography with suitable detectors, or phosphorus determination after extraction. Specifications for MFGM-enriched ingredients list total protein, fat, phospholipid, individual phospholipids such as sphingomyelin, gangliosides, lactose and ash. Because composition depends on the cream, the churning method and the separation steps, suppliers standardise ingredients by blending and fractionation. Claims made for these ingredients in infant formula and other foods are regulated, and the evidence for health effects is still developing, so formulators should rely on the current regulatory position rather than on marketing descriptions.
Ghee residue, the brown solid left after clarifying butter or cream into ghee, is described from the ghee-making side in fat-rich-dairy-products. In large Indian dairies it is produced in significant quantities. It contains a large proportion of fat (often a substantial fraction of its mass, entrained in the non-fat solids), protein (mostly denatured and browned casein), lactose and its Maillard products, minerals and phospholipids. Its composition depends on the method of ghee making: direct-cream ghee produces more residue, with more serum solids, than creamery-butter ghee, and pre-stratification reduces residue by removing serum before heating. Fresh residue is moist and perishable; it turns rancid and mouldy if stored badly.
The first use is recovering its fat: hot residue is pressed or centrifuged, or the fat is extracted with solvents in some industrial processes, to return ghee to the product stream. The defatted residue is a protein-rich material that can be used in confectionery: in India it is used in sweets, chocolate-like products, toffees and bakery fillings, where its cooked, nutty flavour is an asset. Its phospholipids and Maillard products have antioxidant activity, and extracts of ghee residue added back to ghee extend its keeping quality. Ghee residue is also used in animal feed. Valorisation of ghee residue is a good example of how a by-product of a traditional process can be turned into food, antioxidant or feed rather than waste, provided it is handled hygienically.
Permeate is the liquid that passes through the ultrafiltration membrane when milk or whey is concentrated to make milk protein concentrates or whey protein concentrates. It contains the small molecules of the feed: lactose (typically making up the great majority of its solids), minerals, non-protein nitrogen (urea, amino acids, small peptides), water-soluble vitamins and lactic acid in acid systems, with very little protein and fat. As protein ingredients have grown, so has permeate volume, and it has become a significant stream that must be used. Its high lactose content gives it a high BOD, so it cannot be discharged.
Permeate is concentrated and crystallised for lactose manufacture (see the lactose chapter) or dried to dairy permeate powder (also called milk permeate or dairy product solids), which is used in bakery, confectionery, snack seasonings, soups and processed foods as a source of lactose and dairy minerals, partly replacing whey powder or sugar and salt; its minerals contribute a salty, savoury taste, so it is studied as a partial salt replacer. Milk mineral concentrates separated from permeate are used to fortify foods with calcium. Permeate is also used in animal feed, as a fermentation substrate for ethanol, lactic acid, biogas and other bioproducts, and as a raw material for GOS and other lactose derivatives. Delactosed permeate (mother liquor), left after lactose crystallisation, is high in minerals and is used mainly in feed, fertiliser or further processing. Plants that make protein ingredients therefore design their whole product portfolio around permeate use, since the economics of protein concentration depend on it.
Milk minerals, sometimes called milk calcium or dairy minerals, are concentrates of calcium phosphate and other salts obtained from whey or permeate, typically by precipitation of calcium phosphate after heat and pH adjustment, followed by separation, washing and drying. They provide calcium and phosphorus in a form considered natural and are used to fortify dairy products, beverages, bakery goods and nutritional products. Their recovery reduces the mineral load in remaining streams, which improves lactose crystallisation and reduces scaling in evaporators and membranes.
Lactose in whey and permeate can be fermented to ethanol by lactose-fermenting yeasts, chiefly Kluyveromyces marxianus (Saccharomyces cerevisiae cannot ferment lactose without engineering or prior hydrolysis). The overall stoichiometry is: one lactose plus one water gives four ethanol and four carbon dioxide, so the theoretical yield is 4 × 46 ÷ 342 = 0.538 g of ethanol per gram of lactose; practical yields reach a high fraction of this. Because whey contains only about 4.5–5 per cent lactose, the ethanol concentration in fermented whey is low, so concentrating whey or permeate (by reverse osmosis or evaporation) before fermentation raises the ethanol content and reduces distillation energy. Whey-derived ethanol is used for potable spirits (vodka and gin are produced from whey in Ireland and New Zealand, for example), beverages and fuel. Fermented whey can also be made into whey wine or whey beer.
Anaerobic digestion converts the organic matter of whey and dairy effluent into biogas, a mixture of methane and carbon dioxide, by a sequence of hydrolysis, acidogenesis, acetogenesis and methanogenesis carried out by a consortium of micro-organisms. Theoretically, about 0.35 cubic metres of methane (at standard temperature and pressure) are formed per kilogram of COD removed, which is used to estimate energy recovery. Whey is easily degraded but acidifies quickly, so digesters must be designed and operated to avoid souring: high-rate reactors such as upflow anaerobic sludge blanket (UASB) systems, two-stage digestion separating acid formation from methanogenesis, co-digestion with manure, and pH control are common. The biogas can fire boilers or generate electricity and heat for the dairy. Other fermentation products from whey include lactic acid (for food, chemicals and biodegradable polylactic acid), single-cell protein (yeast biomass, for example Kluyveromyces species grown aerobically on whey, used in feed and sometimes food), vitamins, enzymes, polyhydroxyalkanoates (biodegradable plastics), bacterial cellulose and organic acids. Which route is chosen depends on scale, local energy prices, markets for products and environmental rules.
No single route suits every dairy. A small cheese plant with a few thousand litres of whey a day may find whey beverages, ricotta, feed or a share in a regional digester the only practical options. A medium plant may concentrate whey by reverse osmosis to reduce transport cost and sell it to a processor. Large cheese regions support integrated plants that make WPC or WPI, lactose, permeate powder and demineralised whey, with anaerobic digestion of residual streams and dilute effluents to supply energy. The choice depends on whey volume and type (sweet or acid), distance to markets and processors, prices of protein ingredients and lactose, energy prices and incentives for renewable energy, and environmental regulation. Life-cycle and techno-economic assessments are used to compare options, and the general direction is towards using every component — protein, lactose, minerals and finally the residual organic matter as energy — so that nothing is discharged.
A student uses this subject to explain why whey is a pollutant and a resource, calculate BOD loads and population equivalents, WPC concentration, lactose and ethanol yields, and describe demineralisation and casein manufacture. It supports AICE Dairy Technology Unit 4 and practicals in whey beverage and ricotta making.
A by-products or utilities officer five years in runs whey separation, RO and UF plants, sets diafiltration to hit WPC grades, manages lactose crystallisers, monitors effluent BOD and COD, and develops whey beverages or permeate uses. This subject gives the process logic and the mass balances for those tasks.
A plant head decides whether to invest in WPC, WPI, demineralisation, lactose or biogas plants, based on whey volume, markets and environmental rules; negotiates whey supply with cheese plants; and answers to regulators for effluent discharge. This subject frames those investment and compliance decisions.
A professor or research director works on whey protein functionality and fractionation, lactose derivatives, membrane fouling, acid whey valorisation and bioconversion of whey to fuels and biomaterials. They teach and examine AICE Dairy Technology Unit 4 and advise industry and governments on whey policy.
This manual does not yet give: detailed membrane design and fouling control (in membrane-processing-dairy-ingredients); full process conditions for each WPC and WPI grade; standards of identity for whey powder, WPC, lactose and caseinates in specific countries; quantitative digester design; detailed health evidence for MFGM and whey protein claims; and economic comparisons of utilisation routes. BOD, COD, composition and yield values are representative ranges, and the per-person BOD used for population equivalent must be stated in any calculation.
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.
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