Dairy Science & Technology · Dairy Processing & Product Technology · also Cheese Technology, Technology of Cheese and Fermented Products
Cheese from milk selection to ripening and processed cheese: coagulation, curd handling, salting, ripening, yield and the major variety families.
In the exams: ICAR AICE subjects 34 Unit 7, 36 Unit 5 and 37 Units 1 and 7; ICAR AIEEA-PG group 16 (rennet coagulation and ripening) and group 17 Unit I; ACS Certified Cheese Professional (cheesemaking, ripening); Wisconsin Master Cheesemaker coursework
Cheese making turns a perishable liquid into a stable, concentrated food by coagulating casein, removing whey and controlling microbial and enzymatic change. Every variety is a set of choices about milk, coagulant, temperature, acid, salt and time. This manual follows those choices in the order they are made in a plant: milk quality and pre-treatment, coagulants, the chemistry of rennet coagulation, cutting and syneresis, curd treatments such as cheddaring and stretching, salting, ripening, yield, the major variety families, fresh and processed cheese, defects and grading, and mechanised and membrane-based manufacture.
The subject sits where dairy chemistry, dairy microbiology and dairy technology meet, and exams treat it that way. ICAR's AICE-JRF/SRF syllabus asks for the chemistry of rennet action and ripening (Dairy Chemistry), cheese starters and accelerated ripening (Dairy Microbiology) and cheese manufacture, microbial rennet and recombinant chymosin (Dairy Technology). ICAR AIEEA-PG includes rennet coagulation, ripening and Cheddar and processed cheese. Industry credentials such as the American Cheese Society's Certified Cheese Professional test cheesemaking, ripening and evaluation from the practitioner's side. The veterinary track's milk-products-technology gives a one-chapter overview; this manual goes into the science and the numbers.
Values quoted for temperatures, pH and composition are representative textbook ranges. Recipes differ by plant and country, and legal standards of identity, raw-milk rules, permitted additives and salt or moisture limits must always be checked against the current national regulation or protected-designation specification.
Cheese making is a controlled concentration of the casein and fat of milk. Roughly 80 per cent of cow's milk protein is casein, and almost all of it, with most of the fat, is trapped in the curd; most of the water, lactose, whey proteins and soluble salts leave in the whey. Anything that changes the casein micelle, the fat globules, the calcium phosphate balance or the bacterial load changes the cheese. For that reason a cheese plant judges milk on more than fat and solids-not-fat. It wants a high and consistent casein content, a low somatic cell count, low numbers of psychrotrophic and spore-forming bacteria, no inhibitory substances and a normal salt balance.
Milk from late lactation or from cows with mastitis has more whey protein and plasmin, less casein, higher pH and more chloride. It coagulates slowly with rennet, gives a soft gel, loses more fat and fines to the whey and lowers yield. Somatic cell count is therefore a cheese-yield issue as much as a hygiene issue. Colostrum is unsuitable. Milk of different species also behaves differently: buffalo milk has larger fat globules, more casein and more colloidal calcium, forms a firmer gel faster and suits Mozzarella and paneer; goat milk micelles are smaller and its gel is weaker; sheep milk is very rich in solids and gives high yields.
Antibiotic residues, sanitiser residues and bacteriophage inhibit or kill starter cultures, so acid development fails, moisture stays high and pathogens are not suppressed. Raw milk for cheese is screened at reception, and residue-positive milk is diverted. Long cold storage is also harmful: at refrigeration temperature beta-casein and some calcium phosphate move out of the micelle into the serum, rennet coagulation slows, and psychrotrophic bacteria such as Pseudomonas produce heat-stable proteases and lipases that survive pasteurisation and later cause bitterness, rancidity and yield loss.
Most cheese is made from pasteurised milk, typically by a high-temperature short-time treatment equivalent to 72 °C for 15 seconds, which destroys vegetative pathogens. Some traditional and protected varieties are made from raw milk, and many countries permit raw-milk cheese only if it is aged for a minimum period or meets other conditions; the rules differ by country and must be checked locally. A milder thermisation (commonly 57–68 °C for about 15 seconds) is used to reduce psychrotroph numbers in milk that must be stored before use; it is not a substitute for pasteurisation.
Heat treatment above pasteurisation is harmful for rennet cheese. When whey proteins are denatured, beta-lactoglobulin forms a complex with kappa-casein on the micelle surface. This hinders the action of chymosin and the aggregation of renneted micelles, so the gel is weak, sets slowly and holds whey. The extra whey protein retained raises yield slightly but gives a soft, high-moisture curd and poor ripening. For this reason cheese milk is usually not heated much beyond minimum pasteurisation, and heat-treated milk is a known cause of failed rennet gels. Acid-heat coagulated products such as paneer and ricotta are the opposite case, where high heat is used deliberately to bring whey proteins into the curd.
Cheese milk is standardised to a target ratio of casein (or protein) to fat, because that ratio sets the fat-in-dry-matter of the finished cheese, which most standards of identity specify. For Cheddar a casein-to-fat ratio of around 0.7 is common; lower-fat varieties need a higher ratio. Standardisation is done by removing cream, adding skim milk, or adding milk protein concentrate or ultrafiltered retentate; the last approach also raises the total solids and yield per vat.
Calcium chloride is commonly added (often at about 0.01–0.02 per cent of milk, within legal limits) to replace calcium lost to the serum during cold storage and pasteurisation. Extra calcium shortens coagulation time and firms the gel. Nitrate (sodium or potassium) is added in some countries to milk for Gouda, Edam and similar varieties to suppress Clostridium tyrobutyricum and so prevent late blowing; it is restricted or banned elsewhere, where lysozyme, bactofugation or microfiltration are used instead. Colour (annatto) is added to some varieties, and for white cheeses from cow's milk some producers bleach or mask the natural carotene. Starter cultures are added before the coagulant and given a short ripening period so that acid development begins before renneting.
Rennet is the traditional coagulant, extracted from the fourth stomach (abomasum) of young milk-fed calves. Its active enzyme is chymosin, an aspartic protease with a very high specificity for the Phe105–Met106 bond of kappa-casein and low general proteolytic activity. That balance matters: a coagulant must clot milk efficiently but break down other caseins only slowly, or yield falls and bitterness appears. Calf rennet contains mainly chymosin with a smaller share of bovine pepsin; as calves age and eat solid feed, the pepsin share rises, and adult bovine rennet is mostly pepsin. Pepsin is more proteolytic and more sensitive to pH. The ratio of milk-clotting activity to general proteolytic activity (often written C/P) is the usual way to compare coagulants: a higher ratio is better for long-ripened cheese.
Coagulant strength was traditionally expressed in Soxhlet units: the volume of milk that one volume (or mass) of rennet clots in 40 minutes at 35 °C. If a test shows that R millilitres of rennet clot M millilitres of milk in t seconds, the strength is S = 2400 × M / (R × t), because 40 minutes is 2400 seconds. Modern practice uses international milk-clotting units (IMCU) measured against a reference standard by an ISO/IDF method; the two systems are not interchangeable, and the stem of any calculation must say which is meant.
Shortage of calf stomachs and religious and vegetarian demand led to substitutes. Microbial coagulants are aspartic proteases from moulds: Rhizomucor miehei, Rhizomucor pusillus and Cryphonectria parasitica (formerly Endothia parasitica). They are more proteolytic than chymosin, so they can lower yield slightly and cause bitterness in long-ripened cheese. Rhizomucor miehei protease is quite heat-stable and can survive in whey, which matters when whey is processed further; modified (destabilised) forms were developed to reduce this. Cryphonectria parasitica protease is heat-labile and has been used for cheeses cooked to high temperatures, such as Swiss types, where its residual activity is destroyed.
Fermentation-produced chymosin (FPC) is calf chymosin made by genetically modified micro-organisms; production hosts have included Escherichia coli K-12, Kluyveromyces lactis and Aspergillus niger var. awamori. The enzyme is identical to calf chymosin and is now the dominant coagulant in many countries, though its acceptance depends on national rules and on labelling for vegetarian, organic or protected-designation cheese. Camel chymosin made the same way has a higher C/P ratio than bovine chymosin and is used where lower bitterness or better yield is wanted.
Plant coagulants include extracts of the flowers of cardoon (Cynara cardunculus), which give the characteristic soft texture and flavour of some Iberian sheep-milk cheeses, and Withania coagulans berries, used traditionally in parts of South Asia. Fig latex (ficin) and papain clot milk but are too proteolytic for most cheese and tend to give bitter, pasty products.
The choice depends on the variety, ripening time, cost, whey use and the market's rules. Long-ripened hard cheese benefits from the most specific coagulant. Residual coagulant retained in the curd drives primary proteolysis during ripening, so the amount retained matters: more coagulant is retained at lower pH at draining and in cheeses cooked to low temperatures, which is one reason Cheddar and Gouda soften with age while high-cooked Swiss and Italian hard cheeses rely more on plasmin. Dose is set to give the cutting time the plant wants at its milk temperature; overdosing does not make a better gel and adds proteolysis. Coagulants are diluted in cold, chlorine-free water just before addition, because chlorine and high pH inactivate them.
Casein micelles in milk are kept apart by kappa-casein. Its C-terminal segment, the caseinomacropeptide (residues 106–169, glycosylated in part and then called glycomacropeptide), protrudes from the micelle surface as a hydrophilic, negatively charged 'hairy layer' that provides steric and electrostatic stabilisation. Chymosin cuts kappa-casein at the Phe105–Met106 bond. The macropeptide is released into the serum and leaves with the whey; para-kappa-casein (residues 1–105) stays on the micelle. As the hairy layer is shaved off, the micelles lose their stabilisation and become able to aggregate. The enzymatic reaction itself proceeds at refrigeration temperature, although slowly.
Once most of the kappa-casein has been hydrolysed (commonly quoted as about 80–90 per cent), the para-casein micelles begin to aggregate, forming chains and clusters that grow into a continuous three-dimensional network. Aggregation needs calcium ions and is strongly temperature dependent: it is very slow below about 15–20 °C and proceeds well at the 30–35 °C used in most cheese making. This is why milk can be renneted cold and then warmed to coagulate (the principle of cold renneting used in some continuous systems). After the visible clot point the gel continues to firm for some time as more bonds form and micelles fuse; this is the tertiary or gel-firming stage, during which syneresis also begins if the gel is disturbed.
Factors that shorten rennet coagulation time and firm the gel are: higher coagulant concentration, lower pH (down to the point where acid gelation dominates), higher calcium ion activity, temperature up to about 40–42 °C, and higher casein content. Factors that lengthen coagulation time and weaken the gel include high heat treatment of milk, cold storage, high pH (for example mastitic milk), low calcium and high somatic cell count. The Holter relationship states that, under fixed conditions, coagulation time is inversely proportional to enzyme concentration (time × concentration is roughly constant), which is used to adjust dose. The Foltmann approach separates a constant 'aggregation' time from the enzyme-dependent part; any calculation must state which simplified form is being used.
Cheesemakers judge the cutting point by the clean break of the gel on a knife or finger, or by multiplying the visual flocculation time by a variety-specific factor. Instruments measure coagulation objectively: formagraphs and oscillating rheometers record gel firmness against time; optical sensors in the vat detect the change in light backscatter as micelles aggregate and predict cutting time from it. Cutting too early, when the gel is weak, shatters it and loses fat and casein fines into the whey; cutting too late gives a firm gel that releases whey poorly and a higher-moisture cheese. The same micellar chemistry explains why acid gels, formed by lowering the pH to near the isoelectric point of casein (about 4.6), are different: they form without enzyme, dissolve colloidal calcium phosphate, and are more fragile and less able to synerese than rennet gels.
Syneresis is the contraction of the rennet gel and expulsion of whey. It is the main tool the cheesemaker has to set the moisture of the cheese, and moisture in turn governs texture, ripening rate and shelf life. An undisturbed rennet gel synereses slowly; cutting multiplies the surface area through which whey can escape. The para-casein network keeps forming new bonds and rearranging, pulling the strands together and squeezing out whey.
Syneresis increases with smaller curd particle size, higher temperature (cooking or scalding), lower pH (acid development by the starter), more stirring, higher calcium, and time. It is reduced by a high fat content (fat globules obstruct the network), by heat-denatured whey protein in the curd, and by low temperature. The moisture of the finished cheese is therefore controlled by cube size, the cooking temperature and rate, the rate of acid development, stirring intensity and the time from cutting to draining. Most of these act together: for example, a faster starter lowers pH sooner, which both increases syneresis and dissolves colloidal calcium phosphate, changing the final texture.
The gel is cut with wire knives into cubes, small for low-moisture hard cheese (a few millimetres in Parmesan and Swiss types, where the curd is broken to rice-grain size) and larger for soft cheese (Camembert curd may be ladled almost uncut). After cutting the curd is healed briefly and then stirred gently, because fresh curd is fragile and fines are lost if agitation is rough. Cooking (scalding) raises the temperature slowly, commonly by about 1 °C every few minutes at first, so that the curd surface does not harden and trap whey (case hardening). Typical cooking temperatures differ widely by variety: Cheddar is cooked to around 37–40 °C, washed-curd types such as Gouda are heated partly by adding hot water, and Swiss and Italian grana types are cooked to roughly 50–55 °C, which also selects thermophilic starters and inactivates much of the coagulant. These are representative ranges; each recipe sets its own.
Some varieties replace part of the whey with water after partial drainage (curd washing). This removes lactose from the curd so that less lactic acid can form, which gives a higher final pH and a more elastic, less acid cheese; it also lowers the curd temperature or raises it if hot water is used. Gouda, Edam and Colby are washed-curd cheeses.
Whey is drained when the curd reaches the target moisture and acidity, judged by the firmness of the curd, the titratable acidity of the whey or the pH. Curd may be drained into moulds directly (soft cheese), pre-pressed under whey to form a closed texture without mechanical holes (Gouda and Swiss types), or drained and then cheddared or stirred (Cheddar). Pressing fuses the curd particles into a coherent block and expels remaining free whey; pressure and time are set by the variety, and pressing at too high a pressure too early closes the surface and traps whey. The pH at draining is a key control point because it determines how much colloidal calcium phosphate is retained in the curd; lower draining pH means less calcium, more retained coagulant and a softer, more crumbly body.
After the whey is drained, Cheddar curd is allowed to mat together in the vat or on a cooling table. The mat is cut into slabs which are turned and then piled two or more high, and repiled at intervals while lactic acid production continues. This process, cheddaring, lasts until the curd reaches the target pH (commonly about 5.3–5.4 for milling, from around 6.1–6.2 at draining). As the pH falls, colloidal calcium phosphate dissolves and the para-casein becomes more plastic; under its own weight and the warmth of the mat the curd flows and its particles fuse, giving the characteristic fibrous, 'cooked chicken breast' texture. Cheddaring is thus mainly a time for acid development and calcium loss under controlled conditions, not just a mechanical treatment. The mat is then milled into chips, dry-salted, mellowed and hoopped. Stirred-curd (granular) Cheddar and Colby skip the matting and keep the curd separated by stirring, which gives a more open, less fibrous texture; large plants use towers and continuous cheddaring machines to do the same job mechanically.
Pasta filata (stretched-curd) cheeses, including Mozzarella, Provolone and Kashkaval, are made by kneading and stretching acidified curd in hot water or brine. The curd stretches only within a pH window, commonly about 5.2–5.4 for cow's-milk Mozzarella, when enough colloidal calcium phosphate has been solubilised that the para-casein becomes plastic in the heat but the curd has not become so acid that it is brittle and loses fat. If the pH is too high the curd does not stretch; if it is too low it becomes sticky and soupy and loses fat into the stretching water. During stretching at a curd temperature of roughly 55–60 °C the protein strands align into fibres with fat and serum channels between them, which gives the elastic, stringy texture and the melt and stretch of pizza cheese. The heat also kills most starter bacteria and inactivates much of the coagulant, which helps shelf life. Mozzarella for pizza (low moisture) is moulded, cooled and brined; fresh high-moisture Mozzarella is stored in water or light brine and eaten within days or weeks. Buffalo milk gives the traditional high-moisture product in Italy. Cheese made by direct acidification (adding acid rather than relying on starter) reaches the stretching pH faster and is common in large-scale pizza cheese.
Other treatments shape particular varieties. Pre-pressing under whey gives the closed texture of Gouda and Swiss curd. Washing curd lowers lactose (Gouda, Edam, Colby). Cooking to high temperature selects thermophilic flora (Swiss, grana). Soft mould-ripened curd is moulded without pressing and turned to drain by gravity. Blue cheeses are made from loose curd that is not pressed, leaving air spaces, and the cheese is later pierced with needles so that oxygen reaches Penicillium roqueforti inside. Halloumi curd is heated in whey, which gives a cheese that softens but does not melt and run when grilled. Each treatment changes moisture, pH, calcium and structure, and therefore the ripening path.
Salt is a flavour ingredient, but in cheese it is also a processing control. It lowers water activity, slows and finally stops starter activity, controls the growth of non-starter and spoilage organisms, finishes syneresis by drawing whey from the curd, changes the hydration of para-casein and therefore texture, and influences the activity of the coagulant and plasmin during ripening. The concentration that matters biologically is not the salt per cent of the cheese but the salt-in-moisture (S/M), salt as a percentage of the water phase: S/M = salt % ÷ moisture % × 100. A Cheddar with 1.7 per cent salt and 37 per cent moisture has S/M = 4.6 per cent. Commercial graders of Cheddar look at S/M together with moisture in non-fat substance (MNFS = moisture ÷ (100 − fat) × 100), fat in dry matter and pH, because these four together predict how a cheese will ripen.
Salt is applied in three main ways. In dry salting, used for Cheddar and related British varieties, salt crystals are mixed with milled curd chips before hooping. Salt dissolves in surface whey, diffuses into the chips and draws out more whey; some salt is lost in the press whey, so the amount added is more than the amount retained. Uniform distribution is a known problem: uneven mixing gives patches of high and low S/M and uneven ripening.
In brine salting, used for Gouda, Edam, Emmental, Mozzarella, Feta and many others, the pressed or moulded cheese is floated in a concentrated sodium chloride brine (often roughly 18–23 per cent salt, at a cool temperature) for hours to days depending on size. Salt diffuses in and water diffuses out by a slow, diffusion-controlled process, so a salt gradient from rind to centre exists at first and evens out over weeks of ripening. Brine must be maintained: its salt content is topped up, its pH is kept similar to that of the cheese, and calcium is added to brine for some varieties to prevent the rind from softening, because cheese placed in a calcium-free brine loses calcium and its surface becomes slimy. Brines also collect salt-tolerant yeasts and bacteria and must be filtered, pasteurised or otherwise sanitised; Listeria can survive in brine. Surface salting by rubbing dry salt onto the cheese is used for many soft and blue varieties, often combined with brining.
Too little salt in a Cheddar-type cheese allows excessive starter and coagulant activity and gives bitter, acid, pasty cheese; too much slows ripening and gives a dry, salty, crumbly body. Salt also affects how milk fat and moisture are distributed and how a cheese melts. Reducing sodium in cheese is a public-health aim in many countries; options include partial replacement with potassium chloride, which can taste bitter at higher levels, careful control of S/M rather than total salt, and flavour compensation. Any reduction has to be checked for its effect on food safety, because salt is part of the hurdle that controls pathogens and spoilage organisms.
Ripening converts a bland, rubbery curd into a cheese with its own flavour and texture. It is the sum of three primary biochemical events and many secondary ones. Glycolysis is the conversion of residual lactose to lactic acid, mostly within hours or days in Cheddar-type cheese; the L-lactate formed may later be racemised to DL-lactate by non-starter lactic acid bacteria (NSLAB), and calcium DL-lactate is less soluble and can crystallise as white specks on the surface. In Swiss types, Propionibacterium freudenreichii ferments lactate to propionate, acetate and carbon dioxide, classically written as 3 lactate → 2 propionate + 1 acetate + 1 CO2 + 1 H2O (the Fitz equation); the CO2 forms the eyes and propionate gives the sweet, nutty flavour. Surface-mould and smear cheeses lose lactate at the surface to moulds and yeasts, which raises surface pH (deacidification) and softens the cheese from the outside inwards.
Lipolysis releases free fatty acids. It is limited in Cheddar and Gouda but important in blue cheeses, where Penicillium roqueforti lipases act and the released fatty acids are partly oxidised to methyl ketones such as 2-heptanone and 2-nonanone, and in some Italian hard and pasta filata cheeses, where pregastric esterase from rennet paste gives a sharp, piquant flavour. Proteolysis is the most complex event and the main driver of texture change.
Primary proteolysis is done by residual coagulant and by plasmin, the indigenous milk protease. Chymosin hydrolyses alpha-s1-casein at Phe23–Phe24 early in ripening, producing alpha-s1-casein (f24–199), and this cleavage is associated with the softening of Cheddar and Gouda in the first weeks. Plasmin hydrolyses beta-casein into the gamma-caseins and proteose-peptones; it is more important in high-cooked cheese, where coagulant has been inactivated and plasmin activity is raised by the heat that destroyed its inhibitors. Secondary proteolysis is done by the proteinases and peptidases of starter bacteria, released when the cells lyse, and of NSLAB, moulds and smear organisms. They cut large peptides into small peptides and free amino acids. Hydrophobic peptides, if they accumulate, taste bitter; well-balanced cultures with good peptidase activity prevent this. Amino acids are then catabolised by transamination, decarboxylation and other reactions into volatile flavour compounds such as aldehydes, alcohols, acids and sulphur compounds (methanethiol is associated with Cheddar flavour), and into amines, which in excess can cause off-flavours and, in some cheeses, health concerns.
Ripening conditions (temperature, humidity, time, turning, coatings) are set by the variety. Cheddar is commonly ripened at around 6–10 °C for months to years; Swiss types go through a warm room (around 20–24 °C) for eye formation; mould and smear cheeses need high humidity and air movement. Ripening is followed by measuring pH, soluble nitrogen fractions, free amino acids and sensory grade.
Ripening ties up money and storage space, so methods to accelerate it are valuable, provided flavour stays balanced. Elevated ripening temperature is the simplest and cheapest but risks off-flavours from NSLAB. Exogenous enzymes (proteinases, peptidases, lipases) added to milk are mostly lost in whey and those added to curd are hard to distribute; encapsulation in liposomes was developed to address this. Attenuated starters (cells weakened by heat, freezing or lactose-negative mutants) add enzymes without adding acid. Adjunct cultures of selected lactobacilli or other organisms add specific peptidase or flavour-forming activity. Genetically modified starters with overexpressed peptidases were studied, but their use depends on regulation and consumer acceptance. High-pressure treatment has also been studied. Enzyme-modified cheese is a separate product: a paste of young cheese treated with enzymes to develop intense flavour quickly, used as an ingredient rather than as table cheese.
Cheese yield is the mass of cheese made from a given mass of milk, usually expressed as kilograms of cheese per 100 kg of milk. It depends first on milk composition, chiefly casein and fat, and second on how much of each is recovered in the curd and how much water the cheese holds. Whey proteins, lactose and soluble salts contribute little to rennet cheese except in the water phase. Losses occur as fat and curd fines in the whey, as fat in the press whey and in the stretching water of pasta filata cheese, and through excessive proteolysis by a poorly chosen coagulant. Because water is part of cheese weight, moisture has a large effect on yield: one extra percentage point of moisture in Cheddar raises yield noticeably but also changes quality and may break a legal moisture limit.
Typical recoveries in well-run Cheddar making are about 93 per cent of the milk fat and about 96 per cent of the casein, the casein lost being mainly the caseinomacropeptide released by the coagulant. These figures underlie the Van Slyke formula.
The best-known predictive formula, developed for Cheddar by Van Slyke and Publow, is
Y = [(0.93 F + C − 0.1) × 1.09] ÷ (1 − W)
where Y is kilograms of cheese per 100 kg milk, F and C are the fat and casein percentages of the milk, 0.93 is the fraction of fat recovered, 0.1 is the casein lost as caseinomacropeptide and fines (in percentage units of milk), 1.09 is a factor for the salt and other solids carried with the casein and fat, and W is the moisture of the cheese as a fraction. Worked example: milk with 3.6 per cent fat and 2.5 per cent casein, cheese moisture 37 per cent: 0.93 × 3.6 = 3.348; plus 2.5 minus 0.1 gives 5.748; times 1.09 gives 6.265; divided by 0.63 gives a predicted yield of 9.94 kg per 100 kg milk.
Variants are common and an exam stem should say which is used. Some versions use total protein with a casein factor (casein taken as a fixed fraction of protein, often about 0.77–0.78 for cow's milk); some replace 0.93 with a measured fat recovery; some drop the 1.09 factor and add salt and other solids explicitly; and for other varieties the constants differ. A general mass-balance form is: yield = (fat recovered + casein recovered + other solids retained) ÷ (1 − W).
Plants compare actual and predicted yield to find losses. Yield efficiency = actual yield ÷ predicted yield × 100. Fat recovery = fat in cheese ÷ fat in milk × 100, computed from the cheese mass and composition. Because moisture varies from vat to vat, yields are compared on a moisture-adjusted basis: adjusted yield = actual yield × (1 − actual moisture) ÷ (1 − reference moisture). For example, 10.2 kg per 100 kg at 38 per cent moisture, adjusted to 37 per cent, is 10.2 × 0.62 ÷ 0.63 = 10.04 kg. Without adjustment, a vat that simply held more water looks more efficient.
Ways to raise yield without breaking quality or legal limits include: buying milk on casein or protein, controlling somatic cell count and psychrotrophs, standardising casein-to-fat ratio, using a coagulant with a high C/P ratio, cutting at the right gel firmness, gentle handling to reduce fines, recovering fines from whey, and incorporating whey proteins by ultrafiltration or heat treatment where the variety tolerates it.
More than a thousand cheese names exist, but they fall into families defined by the coagulation method (rennet, acid, acid-heat), the moisture content (often expressed as moisture in the fat-free cheese: extra-hard, hard, semi-hard, semi-soft, soft), the ripening agents (bacteria only, internal mould, surface mould, surface smear, propionic eyes) and special treatments (cheddaring, stretching, washing, brining). Many names are protected as designations of origin in some countries and generic in others, so composition and method are defined by national standards or by protected-designation specifications rather than by the name alone. Codex Alimentarius has a general standard for cheese and individual standards for several varieties; national standards may differ.
Cheddar, from England and now made worldwide, is a hard, dry-salted, cheddared cheese from cow's milk using mesophilic starters, ripened from a few months (mild) to two years or more (extra mature). In the United States the standard of identity sets a maximum moisture of 39 per cent and a minimum fat in dry matter of 50 per cent; other countries have their own limits. Gouda and Edam, from the Netherlands, are semi-hard washed-curd cheeses, pre-pressed under whey, brine-salted and coated; mesophilic starters with citrate-fermenting strains produce a few small round eyes. Swiss types such as Emmental and Gruyère use thermophilic starters and propionibacteria, are cooked to high temperature and brined; Emmental is held in a warm room for eye formation. Parmigiano Reggiano and Grana Padano are extra-hard Italian grana cheeses from partly skimmed cow's milk, with thermophilic whey cultures, cooking to about 55 °C, brine salting and long ripening; their protected-designation specifications fix the area, feed and minimum age. Mozzarella and Provolone are pasta filata cheeses.
Blue-veined cheeses are inoculated with Penicillium roqueforti, made from loose unpressed curd and pierced to admit air. Roquefort is made from raw sheep's milk and ripened in caves in southern France; Gorgonzola and Stilton are made from cow's milk. Their flavour comes from strong lipolysis and methyl ketones, and the mould raises the pH as it consumes lactate and releases ammonia. Surface-mould-ripened soft cheeses such as Camembert and Brie carry Penicillium camemberti (often with Geotrichum candidum) on the rind; the mould deacidifies the surface, calcium phosphate migrates outward, and the cheese softens from the rind towards the centre. Smear-ripened (washed-rind) cheeses such as Limburger and Munster are washed with brine to grow yeasts such as Debaryomyces hansenii, which raise the surface pH, followed by coryneform bacteria such as Brevibacterium, giving an orange-red sticky rind and strong aroma. Brined white cheeses such as Feta (a protected designation in the EU for Greek sheep's and goat's milk cheese) and Domiati are ripened and stored in brine. Because soft, high-moisture, higher-pH cheeses support the growth of Listeria monocytogenes, they need particularly strict environmental hygiene.
Fresh cheeses are eaten without ripening. Many are acid-curd cheeses, coagulated mainly by lactic acid from mesophilic starters (or by direct acidification) to around pH 4.6, often with a small amount of coagulant to firm the curd. Cottage cheese is made from pasteurised skim milk: the acid curd is cut into cubes, cooked slowly (commonly to around 50–55 °C) to firm the particles, washed with cold water to remove whey and acid, drained and mixed with a cream dressing. Defects include shattered curd and fines, mealy texture from overcooking, and spoilage by psychrotrophs and yeasts because the dressing is a rich medium; good shelf life depends on post-pasteurisation hygiene and cold chain.
Quark is a soft acid-curd cheese from skim milk; the coagulum is concentrated by a nozzle centrifuge (quark separator) or by ultrafiltration, then cooled and blended with cream, fruit or other ingredients. Cream cheese is made from cream or high-fat mix fermented to about pH 4.6 and then concentrated by centrifugation or ultrafiltration; in hot-pack processes it is heated and homogenised with stabilisers and filled hot, which gives a long shelf life. Its fat and moisture are set by national standards and differ between countries.
Queso fresco and similar Latin American fresh cheeses are made by rennet coagulation of whole milk with little or no starter, followed by salting the curd, moulding and light pressing. They have a high pH and high moisture and are eaten within days. When made from unpasteurised milk or contaminated after pasteurisation they have caused serious outbreaks of listeriosis and brucellosis, so regulators in many countries stress pasteurisation and environmental Listeria control.
Paneer is the South Asian heat-acid coagulated cheese. Standardised milk (buffalo milk or a blend is preferred for texture) is heated to a high temperature, commonly about 90 °C, cooled to around 70 °C and coagulated by adding a dilute food-grade acid such as citric acid, sour whey or lactic acid with stirring until clear greenish whey separates. The curd is hooped, pressed and chilled in cold water. The high heat brings denatured whey proteins into the curd, so yield is higher than for rennet cheese of similar moisture. The coagulation temperature, acid strength and pressing control moisture and the soft, spongy, cohesive body that is wanted for frying and curries. Indian food standards specify maximum moisture and minimum milk fat in dry matter for paneer, with a separate category for low-fat paneer; the exact limits should be taken from the current regulation. Chhana is made similarly but at lower temperature and without pressing, for sweets such as rasogolla and sandesh. Ricotta, from whey or whey with milk, is also a heat-acid product, though it is classed by some as a whey cheese.
Processed cheese is made by grinding natural cheese, mixing it with water, emulsifying salts and optional ingredients (other dairy ingredients, salt, colour, flavours), and heating the mixture with continuous shear until a smooth, homogeneous mass is formed, which is filled hot and cooled. Its advantages are long shelf life, uniform melt and slice, and use of cheese that is misshapen or unsuitable for retail. In natural cheese the protein is calcium para-caseinate, which in heat simply releases fat and separates. Emulsifying salts sequester calcium from this network and exchange it for sodium; the resulting sodium para-caseinate hydrates and disperses, and its exposed hydrophobic and hydrophilic regions act as an emulsifier for the fat released from the cheese. The salts also buffer and adjust pH. Emulsifying salts are therefore not themselves emulsifiers in the usual sense; they make the cheese protein emulsify.
The main emulsifying salts are sodium citrates and sodium phosphates (monophosphates, diphosphates and polyphosphates), and blends of these. Their calcium-sequestering power, buffering capacity and effect on pH differ. Polyphosphates sequester calcium strongly and hydrate protein well but buffer weakly; monophosphates buffer well but sequester weakly; citrates give good slicing properties and are common in block and slice products. The total quantity is limited by law in most countries and is usually a few per cent of the product. During processing the mass thickens with time under heat and shear (the 'creaming' reaction) as protein hydrates and forms a network around fat droplets; controlled creaming gives a firm, sliceable body, while overcreaming makes the mass too thick and grainy. The final pH is usually in the mildly acid range (roughly 5.4–5.9), which balances melt, texture and microbial stability.
The blend of natural cheese also matters. Young cheese with much intact casein gives a firm, elastic, long-texture product suitable for slices; mature cheese with extensive proteolysis gives flavour but a short, soft texture and is used for spreads. Processing temperatures vary with the product and equipment, commonly from about 70 to 95 °C in batch cookers and higher in continuous or UHT-type systems. Cheese spreads have higher moisture and lower fat than block processed cheese and are spreadable at room temperature; cheese foods and analogue products contain other ingredients and are defined by national standards.
Processed cheese is heat-treated and hot-filled, so most vegetative bacteria are destroyed, but bacterial spores, especially of Clostridium species, can survive. Safety rests on a combination of water activity, pH, salt and emulsifying-salt content, sometimes with nisin, and on hygienic filling. Defects include hard, crumbly or grainy texture from excessive creaming or wrong salt; crystals of insoluble salts (for example from some phosphates or calcium citrate) visible as white specks; free fat or oiling off from insufficient emulsification; gas and swelling from spore germination; and browning from Maillard reactions at high storage temperature.
Defects are grouped as flavour, body and texture, colour and appearance. Early gas (early blowing), with many small holes and a spongy body within days, comes from coliforms or yeasts and points to poor milk hygiene or slow acid development. Late blowing in Gouda, Emmental and grana types appears after weeks or months as large cracks and splits with a butyric, rancid smell; it is caused by spores of Clostridium tyrobutyricum that survive pasteurisation and ferment lactate to butyrate, carbon dioxide and hydrogen. Silage feeding is a major source, and control is by feeding practice, bactofugation or microfiltration of milk, nitrate where permitted, or lysozyme. Slits and fractures in Cheddar may come from heterofermentative NSLAB. Bitterness results from excessive coagulant, a proteolytic coagulant, high moisture, low salt-in-moisture or starters with weak peptidase activity. Acid, sour or pasty cheese comes from too much lactose left in high-moisture curd or too fast acid development. Calcium lactate crystals form white specks on aged Cheddar surfaces. Pink discoloration has been linked to certain cultures and to light and oxidation reactions in coloured cheese. Moulds on the surface of vacuum-packed cheese indicate pinholes or leaks.
Cheese is graded by trained graders on flavour, body and texture, colour and finish, using a trier to draw a plug from the block. Many countries have official or industry grading systems: the United States uses grades such as AA, A and B for Cheddar under USDA standards, and India, the UK, Australia, New Zealand and others have their own. University judging uses scorecards with deductions for named defects. Graders also use composition (moisture, fat in dry matter, MNFS, S/M) and pH at a few days old to predict how a young Cheddar will mature and to decide which blocks to sell young and which to hold for maturity.
Large plants have mechanised almost every step. Enclosed horizontal or double-O vats with automated cutting and stirring frames replaced open vats. Cheddar curd is drained and cheddared on continuous belt machines and fed to block-forming towers, where curd under vacuum fuses into blocks of uniform weight. Pre-pressing columns form Gouda-type curd, and continuous cooker-stretchers make pasta filata curd. Automated brining and robotic turning and coating are common.
Membrane filtration changed some cheese families. Ultrafiltration (UF) concentrates casein, fat and whey proteins while lactose, soluble salts and water pass into the permeate. At a low concentration factor UF is used to standardise protein and increase vat throughput. At high concentration the retentate has the composition of the final cheese, so it can be coagulated directly without whey drainage; this is the MMV process (named after Maubois, Mocquot and Vassal), widely used for cast Feta-type cheese, quark and cream cheese. The concentration factor is the mass of milk divided by the mass of retentate: 1,000 kg of milk giving 200 kg of retentate is a five-fold concentration. Because whey proteins are retained, UF raises yield, but native whey proteins are poorly broken down during ripening and the high buffering of retentate slows acid development, so UF is less suited to long-ripened hard cheese. Microfiltration produces micellar casein concentrate and removes bacteria and spores, and bactofugation removes spores by centrifugation, both used against late blowing.
A student uses this subject to understand why each step of a make procedure exists and to do the yield, salt-in-moisture and fat-in-dry-matter calculations that appear in practical records and exams. In the plant training semester it explains what the cheesemaker is watching for at cutting, draining, cheddaring or stretching, and why a vat that runs slow on acid ends up as a defective cheese weeks later. For AIEEA-PG and AICE it supplies the chemistry of rennet action and ripening that is asked every year in some form.
A cheesemaker or quality officer five years in runs vats to a target pH and moisture, adjusts coagulant dose to milk season, checks S/M and MNFS on young blocks, and investigates defects: a run of bitter Cheddar, gassy Gouda, soft brine rinds or poor Mozzarella stretch. This subject gives the cause-and-effect map behind those decisions and the yield-efficiency and moisture-adjusted-yield calculations that show whether a change saved money.
A plant head or technical director decides coagulant policy, whether to invest in UF standardisation or bactofugation, how to pay farmers for casein, and which blocks to hold for maturity. They set specifications with buyers and defend yield and quality figures to the board. The chapters on yield, mechanisation and membrane processes support those capital and contract decisions, and the defects chapter supports root-cause reviews after customer complaints.
A professor or research director works on the frontiers named here: casein micelle and gel structure, the proteolytic and catabolic pathways that form flavour, NSLAB ecology, coagulant engineering, salt reduction and UF and MF-based processes. They teach the PG courses that AICE examines, set questions on coagulation kinetics and ripening chemistry, and advise industry on new varieties and process changes.
This manual does not yet give: step-by-step make procedures with times for each variety; detailed national standards of identity beyond the US Cheddar limits (Codex, FSSAI, EU and others must be checked in the current text); quantitative salt-diffusion modelling; detailed starter-culture taxonomy and phage control, which belong to the starter-cultures subject; cheese packaging; and the economics of whey processing. Temperatures, pH values and compositions are representative ranges; recipes, legal limits on additives such as nitrate, calcium chloride and emulsifying salts, and rules on raw-milk cheese differ by country and should be confirmed locally. The yield formula constants are those of the classic Cheddar form; other varieties and plants use their own.
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.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.