A food product selectively concentrated from major milk components. It is generally rich in flavor and contains high-quality nutrients. There are many varieties of cheese, all produced in the following general manner: Raw or pasteurized milk is clotted by acid, rennet, or both. The curd is cut and shaped into the special form of the cheese with or without pressing. Salt is added, or the cheese is brined after pressing.
Acid is produced during manufacture of cheese by fermentation of the milk sugar, lactose. This fermentation is initiated by the addition of a culture of specially selected acid bacteria (starter culture) to the milk. Acid production in cheese curd retards growth of bacteria that cause undesirable fermentations in cheese. Moreover, it favors the expulsion of the whey and the fusion of the curd particles. Fresh cheese (cottage or cream cheese) does not require any ripening, and it is sold soon after it is made. Other varieties of cheese are cured or ripened to obtain the desirable consistency, flavor, and aroma. The flavor and aroma of cheese are obtained by a partial breakdown of milk proteins and fat by the action of microbial, milk, and rennet enzymes. In hard varieties (Cheddar, Gouda, Edam, Emmentaler or Swiss, and provolone) this is done by the microorganisms in the interior of cheese; in semisoft or soft types (Limburger, Camembert, and Roquefort) by the organisms on, or in contact with, the surface of cheese. See also: Milk
Microorganisms are essential to the manufacture of cheese, imparting distinctive flavor, aroma, consistency, and appearance.
Lactic acid starter cultures are important in making cheese. Different types of lactic acid bacteria (Lactococcus lactis, L. lactis cremoris, Streptoccus thermophilus, and homofermentative lactobacilli) are used, depending upon the kind of cheese desired. The starter (both single and mixed strains of bacteria are used) must convert all milk sugar left in the curd into lactic acid within a reasonable time. Several factors may prevent this: the occurrence of natural inhibitors in milk, antibiotics, and bacteriophages.
Some antibiotics (such as nisin) which affect the activity of the starter may be produced by microbes in the milk. Others may be excreted into the milk by cows treated for a particular disease; this happens if penicillin is used to treat mastitis. See also: Antibiotic
Bacteriophages, or phages, are viruses which lyse sensitive bacterial cells (Fig. 1) and produce new phage particles. Phage particles may get into the milk with infected starter cultures or through contamination with phage-carrying dust particles. Phage particles slow down or totally inhibit the activity of the starter culture, causing insufficient souring and spoilage of cheese. Phage multiplication is influenced by temperature, pH, and calcium content of the medium. Phage outbreaks cause serious economic losses. They can be controlled by rigorous hygienic handling of starters, by culture rotation, or by culturing starters in calcium-free media. Attempts to isolate phage-resistant strains have not met with success. See also: Bacteriophage; Streptococcus
Flora of cheese
Cheeses of the hard type contain lactic acid lactococci and other bacteria present in the starter. Moreover, they contain all the microorganisms originally present in the raw milk or pasteurized milk. The types of bacteria most important for ripening are the lactococci, lactobacilli, micrococci, and propionic acid bacteria. They, together with the enzymes of rennet and milk, break down the proteins to peptides and amino acids, hydrolyze the milk fat to fatty acids, and frequently produce carbon dioxide gas which causes the holes in cheese (Fig. 2). The structure of cheese is greatly changed during ripening.
In semisoft and soft cheeses the lactic acid originally produced by the starter is broken down afterward by molds, yeasts, and bacteria on the surface. The same flora decomposes the protein and the fat to a much greater extent than in hard cheeses. As a result, strong flavors are produced and the structure of the cheese becomes much softer. For the production of blue-veined cheese, needles are pushed into the interior to bring Penicillium roqueforti or the other molds, added during the manufacturing of the cheese, into contact with air they need for growth. The blue color is the color of the mold spores. The red color on the surface of some soft cheeses is caused by Brevibacterium (Bacterium) linens and micrococci. For good surface growth, soft cheeses must be cured in high-humidity air (caves or air-conditioned rooms).
Defects of cheese
In hard cheeses an abnormal gas formation is a problem. It can occur at almost any stage of manufacture or ripening. Early gas production can be caused by coliform bacteria or heterofermentative lactic bacteria. Gas production during cheese ripening (late gas, as in Figs. 3 and 4) may be caused by certain sporeforming bacteria, propionic acid bacteria, Leuconostoc species, and Lactococcus lactis lactis (biovar diacetylactis). The use of L. lactis lactis (biovar diacetylactis) and L. lactis as lactic starter cultures can cause fruity flavors, as well as gas formation, in Cheddar cheese. Other defects of hard cheese include insufficient or excessive acidity, various off flavors, and discoloration. Soft cheeses may be spoiled by gas production, excessive acidity, improper development of surface flora, and contamination with atypical molds.
Cheeses of different ages are blended. The mixture, melted with the aid of emulsifying salts (citrates and phosphates), is packed in sealed containers (tins, paperboard, foil, or plastic). Few bacteria other than sporeformers survive the heat treatment. No substantial growth of the flora takes place in well-preserved processed cheese, but spoilage by anaerobic sporeformers may occur. Clostridium sporogenes causes putrefaction and slit openness and C. tyrobutyricum causes blowing of tins and packages. Acidity, salt content, and temperature of storage are important in controlling spoilage. See also: Industrial microbiology
More than 150 countries make cheese, but 34 countries produce the major commercial quantities. Primitive cheesemaking exists in much of Africa, Latin America, and southwestern Asia, but advanced techniques are also found in these regions. Cheese manufacturing in developed world areas may be simple too, including that for the sheep-milk Broccio of Corsica, the mountain cheese of the Alps, the queso blanco of Venezuela, and the Pennsylvania pot cheese of the United States, but generally it is highly mechanized. Whether the method is primitive or sophisticated, the quality of the resulting cheese is usually excellent.
The primary objective of cheesemaking is to form a smooth acid curd, to reduce the size of the curd block and remove the whey, with or without prior cooking, and to salt and shape the curds. A different type of cheese emerges when the intensity of approximately eight steps is stressed or minimized as required; when special applications, usually microbial, are introduced; and when the environment is transformed to fit the optimum needs of a specific cheese type.
Key materials for cheesemaking include fresh or precultured milk, cultures, milk-coagulating enzyme preparations, special microorganisms, salt, and beta carotene or annatto color. The amounts used and the manner in which these materials are applied strongly influence the cheese character. Cheese may be made from the milk of the cow, sheep, goat, water buffalo, and other mammals, but the milk of the cow is most widely used despite some limitations. Sheep milk and water buffalo milk generally give more flavor to the cheeses, and the color is uniformly white because of a lack of carotene in such mammalian milks, but they are more expensive to make into cheese.
Major classes of cheeses
Two major classes of cheeses exist, fresh and ripened. Fresh cheeses are simpler to make than ripened, are more perishable, and do not develop as intense flavors, but give a mild acid, slightly aromatic flavor and soft, smooth texture.
Three basic groups characterize fresh cheese types: group I—ricotta and Broccio; group II—cottage, Neufchâtel, and cream; and group III—mozzarella. Curd formation for these fresh cheese groups results from a combination of acid (pH 6.0) and heat (176°F or 80°C), as in group I; from acid alone to give a pH of 4.6, as in group II; or from rennet (an enzyme preparation) at pH 6.3, as in group III. Essentially a dehydration of protein occurs, along with a partial or complete reduction of the negative electrical charges which surround the surfaces of the milk proteins. At a critical point, precipitation occurs, leading to a smooth gelatinous curd of varying strength. The curd may be scooped directly into cloth bags or perforated containers for immediate draining and eventual packaging, or the curd is cut and cooked, followed by drainage of whey, salting, and creaming.
Ricotta, or recooked cheese, in its most acceptable form is made from acidified whole milk heated to 176°F (80°C). By introducing large amounts of lactic starter culture, acid whey powder, food-grade acetic or citric acids, and small amounts of salt to cold milk and heating to the above temperatures in a kettle, smooth white particles appear which rise to the top and collect as a curd bed, which is left undisturbed. In about 30 min the hot curd is scooped into perforated containers for drainage and cooled. Later it is removed and consumer-packaged. The product is utilized directly or in a variety of Italian dishes.
Cottage cheese is made from pasteurized skim milk, and in uniform discrete particles classified as small or large curd. A curd forms when the increasing lactic acid of milk during fermentation attains the isoelectric point of casein at pH 4.6. This soft curd additionally contains lactose, salt, and water. Later the curd matrix is cut and cooked to about 126°F (52°C). Separation of whey from the curd is rapid, and is followed by two or three water washings at warm to chill temperatures. Washing removes whey residues and acts as a cooling medium. After drainage of the last wash water, the chilled curd is blended with a viscous, salted creaming dressing to give 4.2% fat and 1% salt, and is packaged. One unsalted, uncreamed, nonfat form of cottage cheese has less flavor, calories, and sodium than standard cottage cheese. Another form is creamed to 9–11% fat and pressed as farmer's pressed cheese. See also: Isoelectric point
Cream and Neufchâtel
Cream and Neufchâtel cheeses resemble cottage cheese in manufacture, but they are made from high-fat mixes instead of skim milk, and no effort is undertaken to attain discrete particles. The minimum fat content of Neufchâtel cheese is 20%, and of cream cheese 33%. The cloth bags traditionally used to separate the whey from the curd have been replaced by centrifugal curd concentrators, which separate the stirred curds and whey at 165°F (74°C). The curd thereafter is pasteurized, treated with stabilizer or gums to prevent water leakage, and salted and homogenized hot. This hot mass is packaged and sealed directly, and tempered at room temperature for a number of hours. The products are used as spreads, in salads, and in cheesecake.
Cottage cheese keeps well at refrigerated temperatures for at least several weeks, but hot-pack cream and Neufchâtel cheeses, because of earlier exposure to high temperature and sealing hot in packages, maintain freshness for up to 2 months or more. Common microbial spoilage agents are molds and yeasts and frequently Pseudomonas bacteria which grow at low temperatures.
Natural mozzarella cheese is normally made from pasteurized whole milk, but milks of 1 or 2% fat may be used if the cheeses are properly labeled. The warm cheese milk is incubated with lactic acid bacteria (Lactococcus lactis, Streptococcus thermophilus, or Lactobacillus delbreuckii bulgaricus), or may be directly acidified by the addition of food-grade acids such as acetic or citric. Added rennet coagulates the milk to a smooth curd, which is cut with wire knives. The curds, without cooking, may be drained of whey shortly after cutting or, depending upon the type of bacteria, may be cooked to 117°F (47°C) before whey removal. The blocks or patties of curd which result from this action are retained until a pH of 5.2–5.5 is achieved, and then are milled into small cubes, placed in hot water, and stretched and molded until smooth. The resulting rectangular blocks are cooled and brined for 2–8 h, depending upon size, and dried and vacuum-packaged.
Acceptable natural mozzarella cheese has a bland, slightly acid flavor. It melts uniformly and smoothly when exposed to hot oven temperatures of 428°F (220°C) for a few minutes and, depending upon type, maintains its quality from several weeks to several months. Natural mozzarella cheese is used in a wide assortment of Italian dishes. Imitations containing vegetable fats, artificial flavors, and a variety of additives are made mainly for institutional and food supplementation use.
Ripened cheese is exposed to an optimum environment of temperature and moisture for a period of time to attain characteristic flavor, texture, and appearance. It may be made from raw, heat-treated, or pasteurized milk that is coagulated with a rennet preparation to form a smooth curd. After cutting and cooking to 95–131°F (35–55°C), the curds are salted, before or after pressing, and shaped. The pressed curds, usually salted, may be given a special microbial application, and then are usually held at 41–59°F (5–15°C) in rooms under controlled humidity (85–95%) to develop the desired traits. All standard ripened cheeses are salted, and the milks from which they are made are always coagulated with rennet, usually in the presence of small amounts of lactic acid and sometimes added calcium chloride.
Rennet milk coagulation occurs when rennin, a protease from rennet, hydrolyzes or splits kappa casein from casein into a whey-soluble component, glycomacropeptide. The cleavage of kappa casein by rennin destabilizes the casein molecule, permitting its dominant alpha and beta casein components in micelle form to precipitate. Such coagulated proteins are filamentous and, through strand overlapping under quiescent conditions, appear as a smooth, homogeneous, sweet (pH 6.3) gel or curd. This curd is cut and cooked, leading to a contraction which expresses whey. The dry curds thereafter are salted, pressed, and ripened. See also: Micelle; Rennin
During ripening, many flavor compounds arise in the cheese. They include free fatty acids, amino acids, ketones, diacetyl, and alcohols. Their amounts in a balanced ratio, along with major components of the cheese, largely determine the characteristic flavor. Agents involved through proteolytic, lipolytic, decarboxylation, and deamination reactions include rennin, natural bacteria of milk, added microorganisms, natural milk enzymes, microbial enzymes, and added food-grade enzyme preparations. The microbial enzymes evolve from millions of microbial cells present in cheese; the sources of the added food-grade enzyme preparations usually are fungal.
Most ripened cheeses are contained in one of six basic groups. The characteristic cheeses in each group include: group I—Cheddar and Monterey; group II—Swiss (Emmentaler) and Gruyère; group III—Edam and Gouda; group IV—Muenster, brick, and Limburger; group V—provolone; and group VI—Camembert, Brie, and blue.
Cheddar and Monterey
For these cheeses the curds are formed at 88°F (31°C) by 0.2 qt (200 ml) of rennet in 2200 lb (1000 kg) of underheated whole milk previously inoculated with 1–2% lactic-type starter for 15–30 min. The curds are cut with wire knives, and cooked to 99°F (37°C) for 30–60 min. Then the whey is run off, and the curd bed is cut into rectangular blocks weighing approximately 11 lb (5 kg). These blocks usually are turned over every 15 min for 2 h in a step known as cheddaring, and the stringy nature of the curd evolves as sufficient lactic acid develops to give a pH of 5.3. The blocks, now flatter than at the start, are milled to small cubes, and dry-salted at the rate of 5 lb (2.3 kg) of salt per 220 lb (100 kg) of curd. These salted curds are pressed in single-service paper or cloth-lined stainless steel boxes. The standard 44- to 66-lb (20- to 30-kg) forms which result are removed, and repressed in plastic films of low oxygen permeability. The film-wrapped Cheddar cheese is ripened up to 1 year at 41–50°F (5–10°C). It is generally manufactured into various-size forms prior to reduction into consumer packages.
In modern industrial cheesemaking, another form of Cheddar cheese, known as barrel, is made by the stirred-curd step in contrast to the cheddaring. This avoids the more lengthy period required for the latter. In the stirred-curd step, individual small cut curd particles, after cooking and whey separation, are stirred for about 30 min, salted, and packed into large film-lined metal or fiber barrels of 640-lb (290-kg) capacity. Here, after excess whey is removed, the curds are pressed and the containers sealed and placed in ripening rooms. Later, the cheese is removed and used largely for making processed cheese. Ripening cheese in large blocks appears to improve typical flavor quality, so that some cheese that is cheddared and destined for long ripening, too, may be held in 640-lb (290-kg) capacity film-lined, sealed boxes.
Monterey cheese resembles Cheddar, but has a higher moisture level and ripens more rapidly. Its curds are washed with water in the vat and not cheddared, but are stirred prior to salting and then added to lined standard stainless steel forms for pressing and eventual ripening.
Swiss (Emmentaler) and Gruyère
Swiss and Emmentaler cheeses are the same, but in the United States the term Swiss is widely used, whereas in Europe and elsewhere the name is Emmentaler. The cheeses are made in block or round forms, but in the United States the former shape dominates because it is easier to slice for sandwiches. Also, economics of production are enhanced.
Underheated milk (158°F or 70°C for 16 s), standardized or partly skimmed, is set with rennet to form a curd, accompanied by three special bacterial cultures, Streptococcus thermophilus, Lactobacillus delbrueckii bulgaricus, and Propionibacterium shermanii. These cultures influence the acid, eye, flavor, and texture development of the cheese. Propionibacterium shermanii is mainly responsible for eye and typical flavor formation.
Renneting requires about 30 min by using 0.2 qt (180 ml) of rennet per 2200 lb (1000 kg) of warm (88°F or 31°C) milk. The size of the curds after cutting is very small, about like peas. These are cooked to about 126°F (52°C) in 60 min, and stirred until the pH decreases to 6.3.
To make block Swiss cheese, these stirred, cooked curds and considerable whey are pumped into cloth-lined, perforated stainless steel chambers. Here a large block is formed under the warm whey, the whey is removed, and the bed of curd remaining is cut into about 100-lb (45-kg) sections. These are immersed in cool brine for up to several days. After removal and drying, the blocks are sealed with plastic or rubberized film, placed in wooden boxes, with room for expansion, and covered by lids. Exposure to warm temperature, about 73°F (23°C) for 2–3 weeks, produces the typical eyes and sweet, hazelnut flavor. Further ripening continues at 41°F (5°C) for 4–12 months before the cheese is ready for market.
Gruyère cheese shows eyes like Swiss or Emmental, but they are usually smaller. This 125-lb (57-kg) round wheel cheese is made mostly in France, Switzerland, and Finland. The surfaces of Gruyère cheese, unlike the larger 224-lb (102-kg) round wheel Emmentals, are not washed daily or wiped with cloths. This leads to a special microbial growth on the surface which imparts to the cheese more flavor of a unique nature best typified by the Comté Gruyère of the French Jura area.
Edam and Gouda
Both of these cheese types may contain eyes, but these are small and lack uniform distribution. Edam cheese is produced in its normal size as 5-lb (2.3-kg) round balls waxed in red. Gouda cheese, softer in body because whole milk is invariably used, appears as orange- or yellow-waxed, medium-sized flat wheels of about 11–22 lb (5–11 kg). Manufacturing is essentially similar for both.
Pasteurized milk is set with lactic culture and rennet, but acid development is constrained usually by removing some of the whey and replacing it with water. Before the cheese is pressed, the pH is usually 5.4. This higher pH gives a sweeter flavor to the cheese and permits other species of bacteria to function. In Europe, where most of this cheese is made, sodium nitrate may be added to the cheese milk to suppress spoilage bacteria, but the practice is diminishing, and instead a continuous bacterial spore centrifugal removal process is substituted. Where nitrates are used, only small amounts are introduced, most of which disappear during ripening.
Unique metal forms shape the cheese after light pressing. The cheeses are brined and waxed. Ripening occurs at 50°F (10°C) for 2–3 months.
Muenster, brick, and Limburger
Good-quality pasteurized milk is required for these cheeses. At times, as for brick cheese, the renneted curd may be washed with water to reduce the acidity and to increase moisture. A reddish bacterium, Bacterium linens, along with yeasts, grows on the cheese surfaces at 59°F (15°C) in a highly moist room for 11 days. The surfaces take on the brick-reddish color of the bacterium. The three cheeses are differentiated by the intensity of their flavor, softness of body, and sizes and shapes. Muenster has least intensity of flavor, followed by brick cheese.
Originating in Italy, provolone cheese also is manufactured in large quantities in Argentina and the United States. It is a pasta filàta, or pulled-curd ripened cheese, and is generally smoked. The texture is smooth and flaky and the flavor highly aromatic or piquante. Initially, the cheese is made almost exactly like that of a fresh, low-moisture mozzarella using Lactobacillus delbrueckii bulgaricus as the starter. Following proper acid development in the vat, the curd is stretched and formed into various shapes: cylindrical, pear, or ball. Thereafter, it is bound with ropes or twine and hung in hickory smoke–filled rooms for 3 weeks or exposed to smoke compounds. Ripening occurs at about 44°F (7°C) for up to 12 months, and cheese sizes range from 3 to 500 lb (1.4 to 227 kg). A related Italian type is caciocovàllo, literally meaning horse cheese.
Camembert, Brie, and blue
These are all rennet cheeses, and Camembert and Brie are made with pasteurized milk cultured to about 0.2% titratable acidity. The curds are not cooked and, following whey drainage and hooping in round forms, they are modified by the special application of white or blue-green mold spores. Introduction of the spores to the cheese may result from inoculating the milk, brine, or curds, or inoculating all three media.
Camembert and Brie are white mold cheeses about 1 in. (2.5 cm) thick whose manufacture is similar except that the diameter of the latter is larger. The characteristic feature of these cheeses is the appearance of a snow-white mat of Penicillium caseicolum or P. camemberti mold on the surfaces. These molds grow well only in an excessive air environment, and hence their appearance on the surface. They ripen the cheese from outside into the center through release of their many active enzymes, which transform the curds to a smooth, soft state. The cheeses are ready for consumption in 12–14 days at 50°F (10°C) and 95% relative humidity. Held thereafter in a refrigerated state for 40 days in supermarkets, the cheeses eventually become overripe. Ammoni- acal flavor with the white surfaces becoming brown and the inner sections becoming light tan confirm an overripe state.
Blue cheese requires spores of Penicillium roqueforti or P. glaucum. These spores, appearing as a black powder, are present throughout the wheel of pressed, highly salted curd, and grow as filamentous blue-green mycelia when minimum air is supplied. In practice, the mold-inoculated wheels of cheese, from 5 to 12 lb (2.3 to 5.4 kg), are penetrated by a mechanical head containing 50 needles which create the long air channels. The mold grows along these air channels, and moves farther into the cheese if natural openings exist. Here the many lipolytic and proteolytic enzymes originating from the mold mycelia attack the cheese to give characteristic flavor. Molding occurs in 30 days after air channel formation at 50°F (10°C) and 95% relative humidity. Then the cheese is held at 41°F (5°C) during 2–6 months for more complete ripening.
The most famous blue cheese is Roquefort, made in southern France from sheep milk. Other widely known related cheeses are Stilton, Gorgonzola, Danish blue, and American blue.
Processed cheese is made from natural types. Nearly any natural cheese can be processed, except that for blue cheese technical difficulties cause blackening of the blue mold due to the high heat.
Processed cheese is produced by grinding selected lots of natural cheese and adding cream, color, salt, and emulsifying agents. The mixture is blended and sent to cookers which heat the mass to 165–185°F (74–85°C). During the cooking, fat normally separates from the protein and water, but this is corrected by adding anhydrous citrate and phosphate salts, usually at 3% levels. The salts raise the cheese pH to about 5.6–5.8, making the protein more soluble. Under these circumstances a stable emulsion of protein, fat, and water occurs to give a smooth homogeneous mass. The hot mass is packaged directly. Processed cheese foods and spreads are made similarly, but include more water and less protein, fat, and other solids.
Sliced processed cheese is attained by spreading the hot process cheese mass emerging from the cookers over moving cold steel rolls. The chilled cheese in thin, wide sheets passes over rotary knives and cutting bars to give squares lying on top of each other, which are packaged in film wrappers.
The cheese industries of the world have become rapid-growth industries with high consumer acceptance of their product. Cheese-manufacturing plants may be very large, utilizing more than 2.2 × 106 lb (106 kg) of cheese milk daily. In the operational areas, cheese vats of 5500-lb (2500-kg) capacity are common, as are giant presses.
Mechanization of cheesemaking too has advanced through the introduction of ingenious cheddaring towers, block formers, and moving web belts. This has led to significantly higher rates of production, with less manual labor, while maintaining quality. True continuous making methods of natural cheese have yet to be realized. However, a unique process incorporating ultrafiltration membrane technology has potential for continuous manufacture of certain cheeses.
Membrane separation is an application of biotechnology to cheesemaking. In this process, skim or whole milk is pumped at low pressure, 48 lb/in.2 (3.4 kg/cm2), through tubes or plates containing many small pores, with a molecular-weight cutoff of 20,000. The milk passes across the membranes, usually at 126–129°F (52–54°C). Much of its water, lactose, soluble salts, and nonprotein nitrogen pass through the pores as permeate. Retained are all the fat, protein, insoluble salts, and some serum, which contains water, lactose, soluble salts, and nonprotein nitrogen. This retentate increases in concentration with time, so that its fat and protein may be five times greater than that of the starting milk. Emerging from the ultrafiltration unit in its final concentrated form as a plastic fluid, this retentate has the same composition as some cheeses. Cheesemaking is completed without vats, as there is no whey to separate. Simple mechanical injection of culture, rennet, salt, color, and fungal spores into the plastic fluid concentrate may follow. A curd develops within 5–10 min, and is placed directly in a ripening room. This is a French process, known as MMV after the names of the inventors, Maubois, Mocquot, and Vassal. Its major advantages are much greater cheese yields due to complete retention of whey protein in the cheese, lower requirements for rennet, a high potential for continuous-process application, and production of a neutral-pH permeate with a reduced biochemical oxygen demand (BOD) value. Much cheese in Europe is made in this manner, particularly fresh, soft acid cheeses—Feta, Camembert, and St. Paulin.
Other variations of ultrafiltration retentate application to cheesemaking include milk retentate supplementation and direct ultrafiltration of cheese milks, but only up to 2:1 protein concentration. The advantages of this alternative ultrafiltration process include improved cheesemaking efficiency, energy savings, and higher quality of marginal cheeses. Use of milk retentates in cheesemaking in this manner has led to the production of natural Cheddar cheese of good quality with significantly reduced sodium levels, 0.015 oz/3.5 oz cheese (420 mg/100 g) or less, compared with approximately 0.02 oz (700 mg) for commercial Cheddar cheeses.
Ultrafiltration has led to whey protein concentrates of 90–95% protein. This nonfat product can be modified to give a texture similar to cheese and is used as a food ingredient to replace butterfat by up to 50% for the making of commercial low-fat cheese. Another technology for the fluid milk and cheese industries is microfiltration. This system follows the same principles as those for ultrafiltration except for membrane pore size. Ultrafiltration retains fat, casein, bacteria, and insoluble salts. Passage through a micromembrane retains fat, bacteria, and insoluble solids, but no protein, making the resulting permeate an almost sterile skim milk. The creamlike retentate obtained is heated to 302°F (150°C) for 2 s, and then it is blended with the almost-sterile skim milk, pasteurized, and cooled to proper temperatures for use in milk and cheese processing. Results from Europe, where much research has been conducted on this subject, indicate an almost 99.5% reduction in total bacteria. Also, quality cheese without gas defects or loss of flavor was produced. See also: Ultrafiltration