CheeseA food product selectively concentrated from major milk components. It is generally rich in flavor andcontains high-quality nutrients. There are many varietiesof cheese, all produced in the following generalmanner: Raw or pasteurized milk is clotted by acid,rennet, or both. The curd is cut and shaped into thespecial form of the cheese with or without pressing.Salt is added, or the cheese is brined after pressing.Acid is produced during manufacture of cheeseby fermentation of the milk sugar, lactose. This fermentationis initiated by the addition of a cultureof specially selected acid bacteria (starter culture)to the milk. Acid production in cheese curd retardsgrowth of bacteria that cause undesirable fermentationsin cheese. Moreover, it favors the expulsionof the whey and the fusion of the curd particles.Fresh cheese (cottage or cream cheese) does not requireany ripening, and it is sold soon after it is made.Other varieties of cheese are cured or ripened to obtainthe desirable consistency, flavor, and aroma. Theflavor and aroma of cheese are obtained by a partialbreakdown of milk proteins and fat by the action ofmicrobial, milk, and rennet enzymes. In hard varieties(Cheddar, Gouda, Edam, Emmentaler or Swiss,and provolone) this is done by the microorganismsin the interior of cheese; in semisoft or soft types(Limburger, Camembert, and Roquefort) by the organismson, or in contact with, the surface of cheese..Cheese MicrobiologyMicroorganisms are essential to the manufacture ofcheese, imparting distinctive flavor, aroma, consistency,and appearance.Starter cultures. Lactic acid starter cultures are importantin making cheese. Different types of lacticacid bacteria (Lactococcus lactis, L. lactis cremoris,Streptoccus thermophilus, and homofermentativelactobacilli) are used, depending upon the kind ofcheese desired. The starter (both single and mixedstrains of bacteria are used) must convert all milksugar left in the curd into lactic acid within a reasonabletime. Several factors may prevent this: theoccurrence of natural inhibitors in milk, antibiotics,and bacteriophages.Some antibiotics (such as nisin) which affect theactivity of the starter may be produced by microbesin the milk. Others may be excreted into the milk bycows treated for a particular disease; this happens ifpenicillin is used to treat mastitis. See ANTIBIOTIC.Bacteriophages, or phages, are viruses which lysesensitive bacterial cells (Fig. 1) and produce newphage particles. Phage particles may get into themilk with infected starter cultures or through contaminationwith phage-carrying dust particles. Phage particles slow down or totally inhibit the activityof the starter culture, causing insufficient souringand spoilage of cheese. Phage multiplication is influencedby temperature, pH, and calcium contentof the medium. Phage outbreaks cause serious economiclosses. They can be controlled by rigoroushygienic handling of starters, by culture rotation, or

by culturing starters in calcium-free media. Attemptsto isolate phage-resistant strains have not met withsuccess. See BACTERIOPHAGE; STREPTOCOCCUS.Flora of cheese. Cheeses of the hard type containlactic acid lactococci and other bacteria present inthe starter. Moreover, they contain all the microorganismsoriginally present in the rawmilk or pasteurizedmilk. The types of bacteria most important forripening are the lactococci, lactobacilli, micrococci,and propionic acid bacteria. They, together with theenzymes of rennet and milk, break downthe proteinsto peptides and amino acids, hydrolyze the milk fatto fatty acids, and frequently produce carbon dioxidegas which causes the holes in cheese (Fig. 2).The structure of cheese is greatly changed duringripening.In semisoft and soft cheeses the lactic acid originallyproduced by the starter is broken down afterwardby molds, yeasts, and bacteria on the surface.The same flora decomposes the protein and the fat toa much greater extent than in hard cheeses. As a result,strong flavors are produced and the structureof the cheese becomes much softer. For the productionof blue-veined cheese, needles are pushedinto the interior to bring Penicillium roqueforti orthe other molds, added during the manufacturingof the cheese, into contact with air they need forgrowth. The blue color is the color of the moldspores. The red color on the surface of some softcheeses is caused by Brevibacterium (Bacterium)linens and micrococci. For good surface growth, softcheeses must be cured in high-humidity air (caves or air-conditioned rooms). Defects of cheese. In hard cheeses an abnormalgas formation is a problem. It can occur at almostany stage of manufacture or ripening. Early gas productioncan be caused by coliformbacteria or heterofermentativelactic bacteria. Gas production duringcheese ripening (late gas, as in Figs. 3 and 4) may becaused by certain sporeforming bacteria, propionicacid bacteria, Leuconostoc species, and Lactococcuslactis lactis (biovar diacetylactis). The use of L. lactislactis (biovar diacetylactis) and L. lactis as lacticstarter cultures can cause fruity flavors, as well asgas formation, in Cheddar cheese. Other defects ofhard cheese include insufficient or excessive acidity,various off flavors, and discoloration. Soft cheesesmay be spoiled by gas production, excessive acidity,improper development of surface flora, and contaminationwith atypical molds.Cheese blending. Cheeses of different ages areblended. The mixture, melted with the aid of emulsifyingsalts (citrates and phosphates), is packed insealed containers (tins, paperboard, foil, or plastic).Few bacteria other than sporeformers survivethe heat treatment. No substantial growth of theflora takes place inwell-preserved processed cheese,but spoilage by anaerobic sporeformers may occur.Clostridium sporogenes causes putrefaction and slitopenness and C. tyrobutyricum causes blowing oftins and packages. Acidity, salt content, and temperatureof storage are important in controlling spoilage.

See INDUSTRIAL MICROBIOLOGY. Norman OlsonCheese ManufactureMore than 150 countries make cheese, but 34 countriesproduce the major commercial quantities. Primitivecheesemaking exists in much of Africa, LatinAmerica, and southwestern Asia, but advanced techniquesare also found in these regions. Cheese manufacturingin developed world areas may be simpletoo, including that for the sheep-milk Broccioof Corsica, the mountain cheese of the Alps, thequeso blanco of Venezuela, and the Pennsylvania potcheese of the United States, but generally it is highlymechanized. Whether the method is primitive or sophisticated,the quality of the resulting cheese is usuallyexcellent.The primary objective of cheesemaking is to forma smooth acid curd, to reduce the size of the curdblock and remove the whey, with or without priorcooking, and to salt and shape the curds. A differenttype of cheese emerges when the intensity ofapproximately eight steps is stressed or minimizedas required; when special applications, usually microbial,are introduced; and when the environmentis transformed to fit the optimum needs of a specificcheese type.Materials. Key materials for cheesemaking includefresh or precultured milk, cultures, milk-coagulatingenzyme preparations, special microorganisms, salt,and beta carotene or annatto color. The amountsused and the manner in which these materials are appliedstrongly influence the cheese character. Cheesemay be made from the milk of the cow, sheep, goat,water buffalo, and other mammals, but the milk ofthe cow is most widely used despite some limitations.Sheep milk and water buffalo milk generallygive more flavor to the cheeses, and the color is uniformlywhite because of a lack of carotene in suchmammalian milks, but they are more expensive tomake into cheese.Major classes of cheeses. Two major classes ofcheeses exist, fresh and ripened. Fresh cheeses aresimpler to make than ripened, are more perishable,and do not develop as intense flavors, but give amild acid, slightly aromatic flavor and soft, smoothtexture.Fresh cheeses. Three basic groups characterizefresh cheese types: group I—ricotta and Broccio;group II—cottage, Neufchˆatel, and cream; andgroup III—mozzarella. Curd formation for thesefresh cheese groups results from a combination ofacid (pH 6.0) and heat (176.F or 80.C), as in groupI; from acid alone to give a pH 4.6, as in group II; orfrom rennet (an enzyme preparation) at pH 6.3, as ingroup III. Essentially a dehydration of protein occurs,along with a partial or complete reduction of the negativeelectrical charges which surround the surfacesof the milk proteins. At a critical point, precipitationoccurs, leading to a smooth gelatinous curd of varying varyingstrength. The curd may be scooped directly intocloth bags or perforated containers for immediatedraining and eventual packaging, or the curd is cut

and cooked, followed by drainage of whey, salting,and creaming.Ricotta. Ricotta, or recooked cheese, in its most acceptableform is made from acidified whole milkheated to 176◦F (80◦C). By introducing large amountsof lactic starter culture, acid whey powder, foodgradeacetic or citric acids, and small amounts of saltto cold milk and heating to the above temperaturesin a kettle, smooth white particles appear which riseto the top and collect as a curd bed, which is leftundisturbed. In about 30 min the hot curd is scoopedinto perforated containers for drainage and cooled.Later it is removed and consumer-packaged. Theproduct is utilized directly or in a variety of Italiandishes.Cottage. Cottage cheese is made from pasteurizedskim milk, and in uniformdiscrete particles classifiedas small or large curd. A curd forms when the increasinglactic acid of milk during fermentation attains theisoelectric point of casein at pH 4.6. This soft curd additionallycontains lactose, salt, and water. Later thecurd matrix is cut and cooked to about 126◦F (52◦C).Separation of whey from the curd is rapid, and is followedby two or three water washings at warm tochill temperatures. Washing removes whey residuesand acts as a cooling medium. After drainage of thelast wash water, the chilled curd is blended with aviscous, salted creaming dressing to give 4.2% fat and1% salt, and is packaged. One unsalted, uncreamed,nonfat formof cottage cheese has less flavor, calories,and sodium than standard cottage cheese. Anotherform is creamed to 9–11% fat and pressed as farmer’spressed cheese. See ISOELECTRIC POINT.Cream and Neufchaˆ tel. Cream and Neufchˆatel cheesesresemble cottage cheese in manufacture, but they aremade from high-fat mixes instead of skim milk, andno effort is undertaken to attain discrete particles.The minimum fat content of Neufchˆatel cheese is20%, and of cream cheese 33%. The cloth bags traditionallyused to separate the whey fromthe curd havebeen replaced by centrifugal curd concentrators,which separate the stirred curds and whey at 165◦F(74◦C). The curd thereafter is pasteurized, treatedwith stabilizer or gums to prevent water leakage,and salted and homogenized hot. This hot mass ispackaged and sealed directly, and tempered at roomtemperature for a number of hours. The products areused as spreads, in salads, and in cheesecake.Cottage cheese keeps well at refrigerated temperaturesfor at least several weeks, but hot-pack creamand Neufchˆatel cheeses, because of earlier exposureto high temperature and sealing hot in packages,maintain freshness for up to 2 months or more. Commonmicrobial spoilage agents are molds and yeastsand frequently Pseudomonas bacteria which growat low temperatures.Mozzarella. Natural mozzarella cheese is normallymade from pasteurized whole milk, but milks of 1or 2% fat may be used if the cheeses are properly labeled.Thewarmcheese milk is incubated with lactic acid bacteria (Lactococcus lactis, Streptococcus thermophilus,

or Lactobacillus delbreuckii bulgaricus),or may be directly acidified by the addition of foodgradeacids such as acetic or citric. Added rennet coagulatesthe milk to a smooth curd, which is cut withwire knives. The curds, without cooking, may bedrained of whey shortly after cutting or, dependingupon the type of bacteria, may be cooked to 117◦F(47◦C) before whey removal. The blocks or pattiesof curd which result from this action are retaineduntil a pH 5.2–5.5 is achieved, and then are milledinto small cubes, placed in hot water, and stretchedand molded until smooth. The resulting rectangularblocks are cooled and brined for 2–8 h, dependingupon size, and dried and vacuum-packaged.Acceptable natural mozzarella cheese has a bland,slightly acid flavor. It melts uniformly and smoothlywhen exposed to hot oven temperatures of 428◦F(220◦C) for a fewminutes and, depending upon type,maintains its quality from several weeks to severalmonths. Natural mozzarella cheese is used in a wideassortment of Italian dishes. Imitations containingvegetable fats, artificial flavors, and a variety of additivesare made mainly for institutional and foodsupplementation use.Ripened cheese. Ripened cheese is exposed to anoptimum environment of temperature and moisturefor a period of time to attain characteristic flavor, texture,and appearance. It may be made from raw, heattreated,or pasteurized milk that is coagulated with arennet preparation to form a smooth curd. After cuttingand cooking to 95–131◦F (35–55◦C), the curdsare salted, before or after pressing, and shaped. Thepressed curds, usually salted, may be given a specialmicrobial application, and then are usually held at41–59◦F (5–15◦C) in rooms under controlled humidity(85–95%) to develop the desired traits. All standardripened cheeses are salted, and the milks fromwhich they are made are always coagulated with rennet,usually in the presence of small amounts of lacticacid and sometimes added calcium chloride.Rennet milk coagulation occurs when rennin, aprotease from rennet, hydrolyzes or splits kappa caseinfrom casein into a whey-soluble component,glycomacropeptide. The cleavage of kappa caseinby rennin destabilizes the casein molecule, permittingits dominant alpha and beta casein componentsin micelle form to precipitate. Such coagulatedproteins are filamentous and, through strandoverlapping under quiescent conditions, appear as asmooth, homogeneous, sweet (pH 6.3) gel or curd.This curd is cut and cooked, leading to a contractionwhich expresses whey. The dry curds thereafter aresalted, pressed, and ripened. See MICELLE; RENNIN.During ripening, many flavor compounds arisein the cheese. They include free fatty acids, aminoacids, ketones, diacetyl, and alcohols. Their amountsin a balanced ratio, along with major components ofthe cheese, largely determine the characteristic flavor.Agents involved through proteolytic, lipolytic,decarboxylation, and deamination reactions includerennin, natural bacteria of milk, added microorganisms,

natural milk enzymes, microbial enzymes, and added food-grade enzyme preparations. The microbialenzymes evolve from millions of microbial cellspresent in cheese; the sources of the added foodgradeenzyme preparations usually are fungal.Most ripened cheeses are contained in one ofsix basic groups. The characteristic cheeses in eachgroup include: group I—Cheddar and Monterey;group II—Swiss (Emmentaler) and Gruy`ere; groupIII—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 areformed at 88◦F (31◦C) by 0.2 qt (200 ml) of rennetin 2200 lb (1000 kg) of underheated whole milk previouslyinoculated with 1–2% lactic-type starter for15–30 min. The curds are cut with wire knives, andcooked to 99◦F (37◦C) for 30–60 min. Then the wheyis run off, and the curd bed is cut into rectangularblocks weighing approximately 11 lb (5 kg). Theseblocks usually are turned over every 15 min for 2 h ina step known as cheddaring, and the stringy natureof the curd evolves as sufficient lactic acid developsto give a pH of 5.3. The blocks, now flatter than atthe start, are milled to small cubes, and dry-salted atthe rate of 5 lb (2.3 kg) of salt per 220 lb (100 kg) ofcurd. These salted curds are pressed in single-servicepaper or cloth-lined stainless steel boxes. The standard44- to 66-lb (20- to 30-kg) forms which result areremoved, and repressed in plastic films of low oxygenpermeability. The film-wrapped Cheddar cheeseis ripened up to 1 year at 41–50◦F (5–10◦C). It is generallymanufactured into various-size forms prior toreduction into consumer packages.In modern industrial cheesemaking, another formof Cheddar cheese, known as barrel, is made by thestirred-curd step in contrast to the cheddaring. Thisavoids the more lengthy period required for the latter.In the stirred-curd step, individual small cut curdparticles, after cooking and whey separation, arestirred for about 30 min, salted, and packed into largefilm-lined metal or fiber barrels of 640-lb (290-kg) capacity.Here, after excess whey is removed, the curdsare pressed and the containers sealed and placed inripening rooms. Later, the cheese is removed andused largely for making processed cheese. Ripeningcheese in large blocks appears to improve typicalflavor quality, so that some cheese that is cheddaredand destined for long ripening, too, may be held in640-lb (290-kg) capacity film-lined, sealed boxes.Monterey cheese resembles Cheddar, but has ahigher moisture level and ripens more rapidly. Itscurds are washed with water in the vat and not cheddared,but are stirred prior to salting and then addedto lined standard stainless steel forms for pressingand eventual ripening.Swiss (Emmentaler) and Gruye` re. Swiss and Emmentalercheeses are the same, but in the United States theterm Swiss is widely used, whereas in Europe andelsewhere the name is Emmentaler. The cheeses aremade in block or round forms, but in the UnitedStates the former shape dominates because it is easier

to slice for sandwiches. Also, economics of productionare enhanced Underheated milk (158◦F or 70 ◦ C for 16 s), standardizedor partly skimmed, is set with rennet toform a curd, accompanied by three special bacterialcultures, Streptococcus thermophilus, Lactobacillusdelbrueckii bulgaricus, and Propionibacteriumshermanii. These cultures influence the acid, eye,flavor, and texture development of the cheese. Propionibacteriumshermanii is mainly responsible foreye 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◦For 31◦C) milk. The size of the curds after cuttingis very small, about like peas. These are cooked toabout 126◦F (52◦C) in 60 min, and stirred until thepH decreases to 6.3.To make block Swiss cheese, these stirred, cookedcurds and considerable whey are pumped into clothlined,perforated stainless steel chambers. Here alarge block is formed under the warm whey, thewhey is removed, and the bed of curd remainingis cut into about 100-lb (45-kg) sections. These areimmersed in cool brine for up to several days. Afterremoval and drying, the blocks are sealed with plasticor rubberized film, placed inwooden boxes, withroom for expansion, and covered by lids. Exposure towarm temperature, about 73◦F (23◦C) for 2–3weeks,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.Gruy`ere cheese shows eyes like Swiss or Emmental,but they are usually smaller. This 125-lb(57-kg) round wheel cheese is made mostly inFrance, Switzerland, and Finland. The surfaces ofGruy`ere cheese, unlike the larger 224-lb (102-kg)round wheel Emmentals, are not washed daily orwiped with cloths. This leads to a special microbialgrowth on the surface which imparts to the cheesemore flavor of a unique nature best typified by theComt´e Gruy`ere of the French Jura area.Edam and Gouda. Both of these cheese types may containeyes, but these are small and lack uniform distribution.Edam cheese is produced in its normal size as5-lb (2.3-kg) round ballswaxed in red. Gouda cheese,softer in body because whole milk is invariably used,appears as orange- or yellow-waxed, medium-sizedflat wheels of about 11–22 lb (5–11 kg). Manufacturingis essentially similar for both.Pasteurized milk is set with lactic culture and rennet,but acid development is constrained usually byremoving some of the whey and replacing it withwater. Before the cheese is pressed, the pH is usually5.4. This higher pH gives a sweeter flavor to thecheese 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 tosuppress spoilage bacteria, but the practice is diminishing,and instead a continuous bacterial sporecentrifugal removal process is substituted. Where nitratesare used, only small amounts are introduced,most of which disappear during ripening.

Unique metal forms shape the cheese after lightpressing. The cheeses are brined and waxed. Ripeningoccurs at 50◦F (10◦C) for 2–3 months.Muenster, brick, and Limburger. Good-quality pasteurizedmilk is required for these cheeses. At times, as forbrick cheese, the renneted curdmay bewashed withwater to reduce the acidity and to increase moisture.A reddish bacterium, Bacterium linens, along withyeasts, grows on the cheese surfaces at 59◦F (15◦C) ina highly moist room for 11 days. The surfaces take onthe brick-reddish color of the bacterium. The threecheeses are differentiated by the intensity of theirflavor, softness of body, and sizes and shapes. Muensterhas least intensity of flavor, followed by brickcheese.Provolone. Originating in Italy, provolone cheesealso is manufactured in large quantities in Argentinaand the United States. It is a pasta fil`ata, or pulledcurdripened cheese, and is generally smoked. Thetexture is smooth and flaky and the flavor highly aromaticor piquante. Initially, the cheese is made almostexactly like that of a fresh, low-moisture mozzarellausing Lactobacillus delbrueckii bulgaricusas the starter. Following proper acid development inthe vat, the curd is stretched and formed into variousshapes: cylindrical, pear, or ball. Thereafter, itis bound with ropes or twine and hung in hickorysmoke–filled rooms for 3weeks or exposed to smokecompounds. Ripening occurs at about 44◦F (7◦C) forup to 12 months, and cheese sizes range from 3 to500 lb (1.4 to 227 kg). A related Italian type is caciocov`allo, literally meaning horse cheese.Camembert, Brie, and blue. These are all rennet cheeses,and Camembert and Brie are made with pasteurizedmilk cultured to about 0.2% titratable acidity. Thecurds are not cooked and, following whey drainageand hooping in round forms, they are modified bythe special application of white or blue-green moldspores. Introduction of the spores to the cheese mayresult from inoculating the milk, brine, or curds, orinoculating all three media.Camembert and Brie are white mold cheeses about1 in. (2.5 cm) thick whose manufacture is similar exceptthat the diameter of the latter is larger. The characteristicfeature of these cheeses is the appearanceof a snow-white mat of Penicillium caseicolum orP. camemberti mold on the surfaces. These moldsgrow well only in an excessive air environment, andhence their appearance on the surface. They ripenthe cheese from outside into the center throughrelease of their many active enzymes, which transformthe curds to a smooth, soft state. The cheesesare ready for consumption in 12–14 days at 50◦F(10◦C) and 95% relative humidity. Held thereafterin a refrigerated state for 40 days in supermarkets,the cheeses eventually become overripe. Ammoniacalflavor with the white surfaces becoming brownand the inner sections becoming light tan confirman overripe state.Blue cheese requires spores of Penicillium roquefortior P. glaucum. These spores, appearing as a

black powder, are present throughout the wheel ofpressed, highly salted curd, and grow as filamentousblue-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 createthe long air channels. The mold grows along these airchannels, and moves farther into the cheese if naturalopenings exist. Here the many lipolytic and proteolyticenzymes originating from the mold mycelia attackthe cheese to give characteristic flavor. Moldingoccurs in 30 days after air channel formation at 50.F(10.C) and 95% relative humidity. Then the cheeseis held at 41.F (5 . C) during 2.6 months for morecomplete ripening.The most famous blue cheese is Roquefort, madein southern France from sheep milk. Other widelyknown related cheeses are Stilton, Gorgonzola, Danishblue, and American blue.Processed cheese. Processed cheese is made fromnatural types. Nearly any natural cheese can be processed,except that for blue cheese technical difficultiescause blackening of the blue mold due to thehigh heat.Processed cheese is produced by grinding selectedlots of natural cheese and adding cream, color, salt,and emulsifying agents. The mixture is blended andsent to cookers which heat the mass to 165.185.F(74.85.C). During the cooking, fat normally separatesfrom the protein and water, but this is correctedby adding anhydrous citrate and phosphatesalts, usually at 3% levels. The salts raise the cheesepH to about 5.6.5.8, making the protein more soluble.Under these circumstances a stable emulsion ofprotein, fat, and water occurs to give a smooth homogeneousmass. 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 spreadingthe hot process cheese mass emerging from thecookers over moving cold steel rolls. The chilledcheese in thin, wide sheets passes over rotary knivesand cutting bars to give squares lying on top of eachother, which are packaged in film wrappers.Production developments. The cheese industries oftheworld have become rapid-growth industries withhigh consumer acceptance of their product. Cheesemanufacturingplants may be very large, utilizingmore than 2.2 ~ 106 lb (106 kg) of cheese milkdaily. In the operational areas, cheese vats of 5500-lb(2500-kg) capacity are common, as are giant presses.Mechanization of cheesemaking too has advancedthrough the introduction of ingenious cheddaringtowers, block formers, and moving web belts. Thishas led to significantly higher rates of production,with less manual labor, while maintaining quality.True continuous making methods of natural cheesehave yet to be realized. However, a unique processincorporating ultrafiltration membrane technologyhas potential for continuous manufacture of certain

cheeses.Membrane separation is an application of biotechnologyto cheesemaking. In this process, skim orwhole milk is pumped at low pressure, 48 lb/in.2(3.4 kg/cm2), through tubes or plates containingmany small pores, with a molecular-weight cutoffof 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 passthrough the pores as permeate. Retained are all thefat, protein, insoluble salts, and some serum, whichcontains water, lactose, soluble salts, and nonproteinnitrogen. This retentate increases in concentrationwith time, so that its fat and protein may be fivetimes greater than that of the starting milk. Emergingfrom the ultrafiltration unit in its final concentratedform as a plastic fluid, this retentate has the samecomposition as some cheeses. Cheesemaking is completedwithout vats, as there is no whey to separate.Simple mechanical injection of culture, rennet, salt,color, and fungal spores into the plastic fluid concentratemay follow. A curd develops within 5.10 min,and is placed directly in a ripening room. This isa French process, known as MMV after the namesof the inventors, Maubois, Mocquot, and Vassal. Itsmajor advantages are much greater cheese yields dueto complete retention of whey protein in the cheese,lower requirements for rennet, a high potential forcontinuous-process application, and production ofa neutral-pH permeate with a reduced biochemicaloxygen demand (BOD) value. Much cheese inEurope is made in this manner, particularly fresh,soft acid cheeses.Feta, Camembert, and St. Paulin.Other variations of ultrafiltration retentate applicationto cheesemaking include milk retentate supplementationand direct ultrafiltration of cheese milks,but only up to 2:1 protein concentration. The advantagesof this alternative ultrafiltration process includeimproved cheesemaking efficiency, energy savings,and higher quality of marginal cheeses. Use ofmilk retentates in cheesemaking in this manner hasled to the production of natural Cheddar cheese ofgood 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) forcommercial Cheddar cheeses.Ultrafiltration has led to whey protein concentratesof 90.95% protein. This nonfat product canbe modified to give a texture similar to cheese and isused as a food ingredient to replace butterfat by upto 50% for the making of commercial low-fat cheese.Another technology for the fluid milk and cheese industriesis microfiltration. This system follows thesame principles as those for ultrafiltration except formembrane pore size. Ultrafiltration retains fat, casein,bacteria, and insoluble salts. Passage througha micromembrane retains fat, bacteria, and insolublesolids, but no protein, making the resulting permeatean almost sterile skim milk. The creamlike retentateobtained is heated to 302.F (150.C) for 2 s, and thenit is blended with the almost-sterile skim milk, pasteurized,

and cooled to proper temperatures for usein milk and cheese processing. Results from Europe,where much research has been conducted on thissubject, indicate an almost 99.5% reduction in totalbacteria. Also, quality cheese without gas defects orloss of flavor was produced. See ULTRAFILTRATION.Frank V. KosikowskiBibliography. J. G. Davis, Cheese, vol. 3: ManufacturingMethods, 1976; F. V. Kosikowski and V. V.Mistry, Cheese and Fermented Milk Foods, 3d ed., 1997; G. P. Sanders, H. E. Walter, and R. T. Tittsler