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Heat Coagulated Cheese
Acid- and Acid/Heat Coagulated Cheese J A Lucey, University of Wisconsin–Madison, Madison, WI, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Generally, acid- and acid/heat-coagulated cheeses have a mild or acidic flavor and are usually consumed fresh (i.e., without ripening). These cheeses usually do not have a rind and come in a wide range of shapes and weights. Fresh acid cheeses (sometimes called lactic cheeses) differ from yogurt and fermented milk products in having a significant amount of moisture removed after coagulation by techniques such as centrifugal separation and ultrafiltration (UF), which are used for Quarg and Cream cheeses, or cutting of the coagulum into granules, which is used in Cottage cheese to encourage syneresis. Soft, unripened cheeses, such as Quarg, Cottage, and Cream cheeses, are related in the common use of lactic cultures to form a smooth acid curd. They differ in the method of whey drainage, washing steps, cream incorporation, and type of curd structure. In Cottage cheese, the coagulum is cut to form curd particles of specific sizes, whereas the coagulum for the other acid- and acid/ heat-coagulated cheeses is usually stirred by agitators and the original curd structure is lost. Many fresh cheeses are also blended with fruits, spices, herbs, or other foods. Fat content can be adjusted even after whey drainage in contrast to natural rennet-coagulated cheeses. Some types of natural cheeses, for example, Mozzarella, are sometimes made by direct acidification but usually rennet is used for coagulation. The main processing steps used in the manufacture of fresh acid- and acid/heat-coagulated cheeses are summarized in Figure 1. Traditional equipment for fresh cheese types consists of fermentation vessels, separation equipment, and packaging devices. However, most fresh cheeses are now made by continuous large-scale processes. The legal designations and standards for these fresh cheeses vary from country to country. Most standards are based on the chemical composition of the cheeses (Table 1). Mesophilic lactic acid bacteria (i.e., mainly Lactococcus spp. and Leuconostoc spp.) and sometimes probiotic species are used as cultures for most acid- and acid/heat-coagulated cheeses. In many of these cheeses, diacetyl, lactate, and acetate are important flavor compounds. Incorporation of whey protein into fresh cheese is an important aspect of fresh cheese manufacture because of increased yield. High-heat treatment of milk is not
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usually practiced for Cottage cheese since heating reduces whey syneresis, which causes textural defects, including excessive softness. The shelf life of fresh acidtype cheeses can be reduced by the growth of yeasts and other spoilage organisms, which can grow due to the high moisture content, absence of a surface rind, and a high level of residual lactose.
Mechanism of Coagulation The stability of casein micelles of milk is attributed to their net negative charge and steric repulsion by the flexible macropeptide region of -casein (the so-called ‘hairs’) (see Milk Proteins: Casein, Micellar Structure). Different types of interactions are responsible for micelle integrity, including calcium-induced interactions between protein molecules, electrostatic and hydrophobic interactions, and hydrogen bonding. On acidification, casein particles aggregate as the negative charge repulsion force on caseins is reduced. This leads to the formation of chains, aggregates, and clusters, which eventually form a three-dimensional network. During acidification of milk, the insoluble colloidal calcium phosphate (CCP) present in casein micelles dissolves and this causes the micelles to swell and become more flexible internally. When milk is subjected to preheat treatment, denatured whey proteins associate with casein micelles and they cross-link the gel network when aggregation occurs during subsequent acidification of milk. Heat treatment increases the firmness of milk gels formed by acidification although these gels can be more susceptible to wheying-off as the gel may undergo greater rearrangement. In gels that are formed from preheated milk, gelation occurs at a higher pH (e.g., 5.2–5.4) than that for unheated milk (pH 5.0); these pH values depend on the gelation temperature. The higher gelation pH can be attributed to the higher isoelectric pH (5.2) of the main whey protein, -lactoglobulin, which initiates isoelectric precipitation/aggregation at a higher pH than that observed with caseins, which have an isoelectric point of 4.6. In acid milk gels produced from heated milk, the solubilization of CCP in casein particles that are already part of the gel network can cause a loosening of the gel network, which assists in curd syneresis. At lower pH values, electrostatic interactions are stronger and the gel becomes firmer again and exhibits less syneresis. In
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Standardized milk Quarg cheese production Fat and protein levels Milk treatments: Pasteurization High-heat treatment Homogenization Acidification Direct acid: Types: citric, acetic, lactic, HCl, H3PO4
Starter culture addition: Level: 0.5–5% Temperature: 20–35 °C
Cold milk (Cottage cheese) Hot (80–85 °C) milk (Queso Blanco cheeses) Optional use of rennet: Level: 0.5–15 ml per 1000 l Formation of acid- or acid/heat-coagulated gel Centrifugation/UF Partial removal of moisture Heating Cutting and syneresis (Cottage cheese) Whey Stirring and centrifugation (Quarg and Cream cheeses) UF (Quarg and Cream cheeses) Curd
Permeate
Cold-pack cheese (Quarg, Cottage cheese, Cream cheese)
Further processing of the curd Heat treatment Hydrocolloid addition Homogenization Shearing
Hot-treated curd
Hot-pack cheese (Cream and Neufchatel)
Figure 1 Main processing steps in the manufacture of acid- and acid/heat-coagulated cheeses (dotted lines are optional processing operations). UF, ultrafiltration.
general, conditions such as high incubation temperatures, fast rates of acidification, and preheat treatment of milk encourage greater rearrangements of casein particles in the gel network and the formation of a coarse network. Direct acidification of milk at a low temperature may allow solubilization of CCP prior to gelation and therefore these gels may undergo less changes in their mechanical properties (e.g., syneresis) than traditional cultured products. The addition of rennet results in gelation at a higher pH and the mechanical properties of the curd are changed. Addition of acid to hot milk (as in acid/heatcoagulated cheeses) causes rapid precipitation of casein (and denatured whey protein), and gelation occurs at
higher pH values than with acid coagulation due to the interactions between denatured whey proteins and casein micelles at the high temperature. The high temperature encourages greater collisions (due to increased thermal motion) of particles leading to faster aggregation. Cottage Cheese Introduction
Cottage cheese, sometimes called Pot cheese, is a creamed, acid-coagulated fresh cheese that is low in acidity and is washed during manufacture. Cottage cheese has a slight acid, salty taste with a delicate diacetyl or creamy flavor and aroma. The body of Cottage cheese should be
700 Cheese | Acid- and Acid/Heat Coagulated Cheese Table 1 Approximate composition of various acid- and heat/acid-coagulated cheeses
Variety Cottage Low fat Creamed Cream Double Single Neufchatel Baker’s Quarg Low fat Creamed Fromage frais (skim) Queso Blanco Ricotta High fat Low fat Ricottone Paneer Mascarpone
Moisture (%)
Fat (%)
Protein (%)
Salt (%)
pH
79 79
2 5
14 13
1.0 1.0
4.8–5.0 4.8–5.0
54 70 64 74
33–35 14 20 0.2–0.6
8–10 12 12 19
0.7–1.2 0.7–1.2 0.75 <0.10
4.6–5.0 4.6 4.6 4.4–4.6
82 73 86 48–55
0.5 12 1 15–27
13–15 10 8 19–24
0.1–0.7 0.1–0.7 0.1–1.0 2.3–3.0
4.5 4.6 4.4 5.2–5.7
72 75 73–82 50–55 40–52
13 8 0.5 25–27 45–50
11.5 12 11–19 16–18 2.5–7.5
<0.5 <0.5 <0.5 0.0 0.0
5.8 5.8 4.9 5.4 5.6–6.4
smooth and meaty, and curd particles should be discrete but not soft and pasty. Cottage cheese is popular in the United States (where total production was 360 000 tonnes in 2007), the United Kingdom, and several other countries, and is often used in combination with salads and desserts. Cottage cheese accounts for around 5% of the world’s cheese production. Recent innovations/developments include the addition of probiotic cultures and prebiotics, extension of shelf life through the incorporation of carbon dioxide into the dressing, smaller more convenient single-serve containers, calcium fortification, use of bacteriocinproducing cultures, fruit-flavored products, and the use of UF to increase the total solids (TS) content of the cheese milk. Manufacturing procedures
Cottage cheese is made from pasteurized skimmed milk (in contrast to several other fresh acid cheeses where the milks are often subjected to higher heat treatments). The TS content of the skim milk is often increased to 10–13% by fortification with nonfat dry milk powder (NFDM;
skim milk powder) or by the addition of UF retentate. There are at least three different procedures for the manufacture of Cottage cheese based on the length of the setting time prior to cutting: long-, medium-, and short-set methods (Table 2). The length of time before cutting varies from 5 to 16 h and the temperature of setting ranges from 22 to 35 C. A higher level of starter inoculum and high incubation temperature are used in the short-set method compared with the slow long-set method. Non-gas-producing mesophilic cultures (e.g., Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris) are usually used. Recently, in the United States, there has been a trend away from bulk starter and towards direct vat inoculants. A low level of rennet (1–3 ml per 1000 l milk) may be added, which helps to form a suitable gel after a shorter incubation period. Rennet is often added after some acidity has developed by the starter culture (e.g., after 1–2 h). When rennet is added, the gel is ready to be cut at a higher pH (e.g., 4.75) than in its absence (e.g., 4.6). After cutting, the curd is left undisturbed for 15–35 min. Curds of different sizes are produced by cutting the coagulum
Table 2 Some of the processing conditions commonly used for the production of Cottage cheese Process step
Short set
Medium set
Long set
Rate of starter addition (%) Conventional bulk starter pH-controlled starters Time before cutting (h) Incubation temperature ( C)
5 2 5 30–33
2 1 8 27
1 0.5 12–16 21–24
Cheese | Acid- and Acid/Heat Coagulated Cheese
with different-sized knives. After this resting period, the curds are cooked slowly with gentle stirring for 1–3 h until a temperature between 47 and 56 C is reached. Cottage cheese curd is fragile and shattering occurs if the curd is mishandled. When the same vat is used for the complete production operation, the curds are normally washed three times with water at a decreasing temperature, for example, 28–22, 16–10, and 5–2 C. Washing removes lactose and lactic acid, and cools the curd to slow down further acid production and syneresis. The total time for washing and drainage steps is 3 h. After all the water has been drained off, pasteurized cream (10–20% fat) at 4 C containing a small amount of salt and stabilizers (e.g., xanthan gum, carrageenan, and/or guar gum), known as ‘dressing’, is added and mixed into the curd. In the United States, creamed Cottage cheese contains 79% moisture, 16% solids nonfat, 4% fat, and 1% salt. After a short holding time, the curds are packed into containers (e.g., vacuum-formed polystyrene tubs with a shrink film of polypropylene) and stored at 4–5 C for retail distribution and they have a typical shelf life of up to 3–4 weeks (in the United States). Cottage cheese can also be made by direct acidification of cold milk (4 C) to pH 5.2–4.7. Milk is usually acidified to pH 5.1 with hydrochloric, phosphoric, lactic, or other acids and then warmed to a higher temperature, for example, 32 C, when a small amount of the acidogen, gluconic acid--lactone (GDL), is added to the milk to reduce the pH of milk to 4.7. The milk then coagulates and the curd is treated as normal. Using this approach, slow acidification of milk can be achieved, whereas addition of a high concentration of GDL at a high temperature would cause a rapid reduction in milk pH. Equipment
Most Cottage cheese is made in rectangular, open vats but the whey draining, curd washing/cooling, and creaming steps may be performed in separate equipment, which improves process efficiency (e.g., reduces water usage). The main processing equipment for Cottage cheese includes plate heat exchangers (to pasteurize the milk), milk fermentation tanks, cutting devices, stirring area with indirect or direct heating, whey drainage belts with curd washing stations/tanks, pressing belt, area for addition of dressing (in vats or by mixers), and a packaging/ filling system. Several types of heating systems are used, including drawing whey from the top of the vat and passing it through a heat exchanger and ‘jet cooking’, which is similar to the previous system except that culinary steam is injected into the whey. Uniform heating is critical to prevent ‘burn-on’ during the cooking stage. Gentle agitation is required as the curd is fragile; several agitator designs have been developed including vertical stirring motion (e.g., the Vert-Stir from Stoelting) to minimize damage.
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Defects
Minor sludge formation is a defect that can occur during Cottage cheese manufacture. This ‘sludge’ is caused by agglutination of starter bacteria and milk proteins, which can occur during the incubation period. Homogenization of the skim milk and careful selection of starter cultures are two methods commonly used to reduce the likelihood of this defect occurring. A ‘floating curd’ defect can also occur during cooking of Cottage cheese curd and is usually attributed to cultures (e.g., citrate-positive strains of Lc. lactis) that may produce excessive amounts of carbon dioxide. Careful selection of starter cultures for both acid- and flavor-producing ability is necessary. The defect called ‘major sludge formation’, where all the curd seems to form a sludge at the bottom of the vat, is usually thought to be due to phage infection of the vat during fermentation. In contrast to most other fresh cheeses, Cottage cheese has a granular, curdy texture rather than a viscous, smooth, or pasty body. Sorbates and other preservatives are often used to increase shelf life. Another approach to increase shelf life is injection of carbon dioxide (about 600–1100 mg kg 1), which is injected directly in the cream line. Carbonated cream enters the cream/curd mixer and the product is barrier packaged. The increase in shelf life (up to 8 weeks) depends on the amount of carbon dioxide initially dissolved in the product and the barrier properties of the packaging system during storage.
Cream Cheese Introduction
Cream cheese includes several closely related products including single Cream cheese, double Cream cheese, Neufchaˆtel (spelled Neufchatel in the United States), and Bakers’ cheese. In Germany, Rahmfrischka¨se (rahm means cream in German) is a type of single Cream cheese, while Doppelrahmfrischka¨se is a type of double Cream cheese. Cheeses that are closely related to Cream cheese are produced in other countries, for example, PetitSuisse, Gournay, Bondard, Fromage a la Cre`me, and Carre´ Frais (carre´ meaning ‘square’) in France (some of these cheeses have a white surface mold). In the US standards of identity, Cream cheese must contain a minimum of 33% fat and a maximum of 55% moisture. Cream cheese is very popular in the United States, with total production of Cream and Neufchatel in 2007 around 350 000 tonnes. Cream cheese was first made in the United States in 1872. Cream cheese is used on bagels, in salads, and as an ingredient in flavored spreads, frostings, and cheesecake. In some countries, a Cream cheesetype product is made by combining a Quarg-like curd with cream or butter. Imitation cream cheese involves substitution of some or all the milk fat with vegetable fats.
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Neufchatel cheese must contain 20% but <33% fat and a maximum of 65% moisture. Bakers’ cheese is produced in the United States and is widely used in the bakery and confectionary trades, hence its name. It is made from skim milk and has a soft, dry, grainy, pliable curd. Neufchatel cheese is made from milk with 5% fat but otherwise by a procedure similar to that of Cream cheese; owing to its lower fat content, it has a grainier body and is less smooth than Cream cheese. The traditional French version of Neufchaˆtel may be made from whole raw milk that is heated to around 20–30 C, at which point a small quantity of rennet is added and the milk allowed to coagulate for 1–1.5 days. During this coagulation period, the milk sours due to its adventitious microflora. The curd is hung in cloth bags to drain for half a day, after which pieces of mature Neufchaˆtel are added and the curd put into molds and covered and salted. The curd is allowed to age for about 10 days, although it can be aged longer. The rinds develop a white surface mold. Recent innovations in Cream cheese include nonstandard of identity (United States) products that are designed to be more spreadable, whipped cream cheese, bagels with cream cheese in one container, wheyless cream cheese made with transglutaminase (see Enzymes Exogenous to Milk in Dairy Technology: Transglutaminase), and shelf-stable cream cheeses (processed cream cheese). Manufacturing procedures
Single (fat) Cream cheese is made from milk with a fat content of 3–3.5%, while double Cream cheese is made from milk containing 8–14% fat. Industrially, there is trend of using higher TS in cheese milks to help reduce the amount of (acid) whey that would be needed to be removed from curd during cheesemaking. Milk is standardized and homogenized (e.g., 12–17 MPa at 50 C) and cooled to 31 C for a short-set (incubation time 5 h) and 22 C for a long-set (incubation time 12–16 h) procedure. Then, the starter is added (e.g., 2%), the level of which depends on the incubation period and temperature. At the end of incubation, the pH is 4.7–4.8. In some processes, a small amount of rennet may be added (e.g., 5 ml of standard rennet per 1000 l milk) with the starter, but is not essential. The gel is broken using agitators and heated to 40–55 C (to encourage syneresis and efficient separation), when whey is separated from the curd using either a Cream cheese separator or UF (operating temperature is usually 50–55 C to reduce viscosity while concentrating). Traditionally, whey was drained using cloth bags. There are two main product types, cold-pack and hotpack products. In the manufacture of cold-pack Cream cheese, after whey separation, the cold curd (10–12 C) is salted, stabilizers are added, and the product is packaged. Typically, around 0.3% of a single stabilizer or combination of several stabilizers, such as locust bean
gum, guar gum, xanthan gum, and carrageenan, is added. Stabilizers are added to help prevent syneresis and the appearance of free moisture on the surface of the product during storage. In some Cream cheese products, whey protein concentrates are also added as a stabilizer. In the hot-pack process, the curd is mixed with salt and stabilizers in kettles or scraped-surface heated vats and heated to 65–70 C. The hot curd (65–70 C) is then pumped into packages and subsequently allowed to cool. The curd is sometimes heated to temperatures as high as 80 C to aid mechanical separation of whey and this further heat treatment of the curd may be carried out in a tubular heater. Instead of a tubular heater, the hot (70–75 C) product may be homogenized at 12–15 MPa. Cream cheese is also made by direct acidification (using organic acids) of milk.
Equipment
Essential equipment for cold-pack Cream cheese and (United States) Neufchatel includes basic mix pasteurizing vats, homogenizer, plate surface or tubular heat exchangers, fermentation vats, balance tanks, mechanical separator or UF unit, centrifugal and positive displacement pumps, fillers, blenders, and packaging lines. Tubular heat exchangers are often used to cool the viscous cheese for cold-pack products. For hot-pack Cream cheese, large jacketed vats with agitators or a scrapedsurface heat exchanger and an additional homogenizer for the hot mix are also required. Double Cream cheese separators have a design different from that of Quarg separators because the higher fat content results in ejection of the whey (being heavier) toward the bowl wall, and ejection of the cheese product toward the center.
Texture and defects
If the pH of the cheese is too high (i.e., >4.7), the texture will be soft and the cheese will lack flavor. At a very low pH (<4.6), the texture may become too grainy and the flavor too acidic. Defects in these cheeses include whey separation from the product during storage and a grainy chalky texture, especially in the lower fat types. Hotpack cheese has a more brittle texture than the coldpack product due to the additional heating and shearing treatments. Cream cheese should be spreadable as it is commonly used on bagels and in cheesecakes. Cream cheese is often sold in plastic tubs, in cartons, or wrapped in metal foil, and is often blended with various flavors, herbs, and spices. The shelf life of the cold-pack product is only a few weeks, whereas the hotpack cheese has a shelf life of up to 3 months on refrigerated storage. Improperly stored or packaged Cream cheese can undergo lipid oxidation, which can limit its shelf life.
Cheese | Acid- and Acid/Heat Coagulated Cheese
Quarg Introduction
Quarg (Quark) is another fresh cheese that is often mixed with cream, fruit, or seasonings. Quarg is a smooth, soft, spreadable paste, which is used in many home-prepared foods and dishes. This cheese is popular in central Europe (e.g., Germany, Poland, and Austria). Other names for this type of product in different countries include Kvarg, Tvarog, Tworog, Twarog, Sauermilchquark, and Speisequark. Chakka, a product related to Quarg, is popular in India; it is a fermented curd formed by acid coagulation of milk at 28–30 C and drainage of whey using muslin bags. Shrikhand (also spelled Srikhand) is a fresh cheese made in India by mixing sugar and spices to Chakka. Fromage frais (fresh cheese) is a cheese related to Quarg and is produced in France and some other European countries. Fromage frais products are produced with a range of fat contents and are often blended with fruits. These cheeses are marketed as chilled (dairy) desserts. Similar products are produced in other parts of the world. In Germany, several cheeses (e.g., Harzer, Mainzer, and Handkaese) are made from an acid curd (Quarg-like) product by allowing a surface flora (smear) to develop and therefore this type of cheese undergoes ripening. Manufacturing procedures
The dry matter content of nonfat Quarg varies from 14 to 24%; for example, in Germany, the minimum TS and protein contents of soft cheese are 18 and 12%, respectively. The protein content of nonfat Quarg varies from 12 to 18%. The higher levels of solids are harder to achieve using UF or a Quarg separator than by the traditional process. Traditional Quarg was separated from whey using filter cloths or muslin bags (i.e., in batches). Quarg-like products with many different fat contents are manufactured in European countries. In the traditional manufacture of Quarg, the milk is pasteurized just before fermentation. However, severe heat treatment of milk, which denatures whey proteins, is now commonly used in the manufacture of Quarg. There are two main processes for the manufacture of Quarg, thermoquarg and UF Quarg. In the thermoquarg process, milk is subjected to a high-temperature–long-time pasteurization at 85–95 C for 3–15 min (using a long tubular holding section in the heat exchanger) and further treatment (56–60 C for up to 3 min) of the acidified milk before cooling to 40 C for centrifugal separation. Both heat treatments are considered to give a higher yield (10%) because of the incorporation of denatured whey proteins. In the Centriwhey and Lactal processes, Quarg whey is heat-treated (e.g., 95 C) and concentrated (these two methods differ in the TS content of the denatured whey product), and the denatured
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protein is then added back to cheese milk used to make the next batch of Quarg. This process is used to alter the texture and increase cheese yield. The main difference between thermoquarg and UF Quarg processes is that whey is separated by UF in UF Quarg. After heat treatment, milk is cooled to 20–28 C and a starter culture (Lc. lactis subsp. lactis, Lc. lactis subsp. cremoris and/or Leuconostoc spp. and citrate-positive strains of Lc. lactis) is added (0.3–4%) together with a small amount of rennet. The level of rennet added is usually about 10% of that used in the manufacture of rennet-coagulated cheese, that is, 5–15 ml standard rennet per 1000 l milk. Often, some acidity (e.g., pH 6.3) is allowed to develop (e.g., 60–90 min after the addition of starter cultures) before rennet is added. This gives a firmer coagulum in high-heat-treated milk. After 16 h, when the gel is at pH 4.6, the coagulum is stirred. In a short-set method, a temperature of 27–30 C is used and the incubation time is 5–6 h. The mix is then heated (e.g., 60 C for 1–6 min) and separated using either a Quarg (centrifugal) separator (operating temperature 32–44 C) or UF membranes (operating temperature 40–45 C), both working in a continuous mode. If the Quarg is creamed, an appropriate amount of sweet or cultured cream is added prior to packaging. The shelf life is usually 2–4 weeks with refrigerated storage. For a long-life Quarg, the final product is heat-treated, which helps to reduce bacterial numbers. Suitable stabilizers are added to a buffer tank after separation and prior to final heating.
Equipment
A Quarg production line is similar to that for Cream cheese and contains fermentation tanks, plate heat exchangers, Quarg separator/UF unit, positive displacement pumps, plate coolers, creaming tank or mixer (if fat is added), and a filling/packaging system. Quarg separators are somewhat similar to cream separators but the bottom part of the bowl is equipped with nozzles through which curd is discharged continuously.
General properties
Quarg from skim milk is smooth and white with a mild clean, acid flavor. Addition of cream gives extra flavor and smoothness. Excessively high calcium and rennet levels are considered to be associated with a ‘bitter’ taste defect. Quarg can also be made using partially concentrated milk, followed by acidification, coagulation, and UF separation. Acidification of the partially concentrated milk prior to UF helps to reduce the calcium content of the final cheese. Gelatin or other hydrocolloids are sometimes added to Quarg as stabilizers.
704 Cheese | Acid- and Acid/Heat Coagulated Cheese
Acid/Heat-Coagulated Cheeses Queso Blanco or Hispanic Cheeses Several types of fresh acid/heat-coagulated cheeses are made in Latin American countries under the general name Queso Blanco (also called Hispanic or white cheeses). Many types of Queso Blanco cheeses, for example, Queso Fresco, Queso de Prensa, Queso de Puna, Queso de Hoja, Llanero, and Quesillo, are usually coagulated with rennet. The manufacturing procedure (e.g., the use of rennet or acid/heat to coagulate the milk) for Queso Blanco cheeses can vary from country to country and also from the traditional (farm) process to that used in modern factories. The acid/heat-coagulated Queso Blanco cheeses (such as Queso del Pais, Queso de la Tierra, and Queso Sierra) are usually made from skimmed, partially skimmed, or whole milk that is pasteurized at 80–85 C. Acidulants (e.g., acetic, lactic, or citric acid) are added to the hot milk to bring the pH to 5.0–5.4 and then stirred, dewheyed, and salt and flavors added. The mixture is then pressed, packaged, and stored. In traditional methods for the production of these types of cheese, the milk is acidified by the addition of vinegar, lemon juice, or other fruit juices that are available locally. For some cheeses, after curd has been precipitated and cooled to 32 C, a lactic starter culture (mainly Lactobacillus spp.) may be added to give additional flavor to the cheese; the cheese is then packaged as usual.
5.4 with citric acid and heated to 80 C to recover additional whey proteins and is used to make Ricottone cheese (sometimes whole milk is added to the whey). In a recently developed continuous Ricotta process, blends of full-fat milk and whey are heated to 90 C and directly acidified with acid to pH 5.3–5.5, which results in precipitation of the protein. The curd is then separated from the whey on a conveyor belt and hot packaged. Ricotta is often used in baking and confectionary applications. Requeso´n is a spreadable Hispanic cheese that is similar to Ricotta.
Mascarpone Mascarpone is a traditional soft Italian cheese that is made from hot (85–90 C) cream (e.g., 25–35% fat) that is acidified with acid (e.g., acetic, citric, or tartaric acid) to pH 5.7–6.4. The curd formed is drained in cloth bags (for long periods, e.g., 20 h), mixed or whipped, and packaged. The cheese is consumed fresh (unsalted or lightly salted) and it is pale or cream-colored, with a mild creamy (slightly tangy) flavor and a thick, spreadable consistency. This cheese is often used in cakes or to make desserts (e.g., Tiramisu). Membrane filtration or separation has replaced the cloth bags. Recently, higher fat creams have been used in conjunction with UF and hot filling in order to speed up the long curd drainage time required with the traditional process; this process also increases yield and improves shelf life (up to 45 days at temperatures 4 C).
Ricotta and Ricottone Cheeses Ricotta cheese was traditionally made in Italy from the whey from sheep’s milk cheese, which was heated to denature and coagulate the whey proteins; the coagulated protein was scooped from the whey. The traditional process has been modified in some countries due to the increasing popularity of Ricotta, which is now often made from milk or milk/whey mixtures. Dried whey protein powders have also been used in the manufacture of Ricotta. In the traditional (batch) process, whey (or milk/whey mixtures) is acidified to pH 5.6–6.0 with starter culture or acid (e.g., acetic or citric acid) and heated to 80 C by stream injection or by indirect heating of the vats. The flocculated protein rises to the surface where it is collected and separated from the whey and placed in molds for further drainage. Calcium chloride is sometimes added to improve flocculation. The curd may be homogenized to produce a smoother consistency. UF is now often used to concentrate the whey (or milk/whey mixtures) prior to or after acidification and the retentate is concentrated to 30% TS. The UF retentate is then heated and hot packaged. Acidification can also be carried out by the addition of acid whey powder to milk. The whey derived from Ricotta cheese can be acidified to pH
Paneer Paneer, another acid/heat-coagulated cheese, is popular in India and the Middle East. It is made from cows’ or buffaloes’ milk. The milk is heated to 85–90 C, cooled slightly (e.g., to 72 C), and lemon juice, citric acid, or sour whey is added to coagulate the milk (which usually takes only a few minutes). Sometimes a small quantity of calcium chloride is added to the hot milk to aid coagulation. The coagulated milk is stirred gently and the curds are separated from the whey by straining through cheese cloth. The curds are placed in hoops and lightly pressed, cooled using chilled water, packaged, and stored (usually no salt is added). The moisture content of the cheese is typically 50–55% and the pH is 5.4. In India, the regulations for Paneer indicate that it should not contain more than 70% moisture and the milk fat content should not be less than 50% of the dry matter. Versions of this cheese are made in India by different methods, including using rennet to coagulate the milk (e.g., Panir), allowing milk to sour naturally before heating, or adding sour buttermilk to freshly boiled milk. Chhanna or Channa (which is also produced in India) is very similar to
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Paneer cheese except that the curd is not pressed. In India, the regulations for Chhana indicate that it should not contain more than 70% moisture and milk fat should not be less than 50% of the dry matter. The shelf life is usually no more than about 6 days with refrigerated storage.
volume of acid whey produced during curd/whey separation.
Derived Products
Further Reading
Acid whey is the major by-product from acid- and acid/ heat-coagulated cheeses. The composition of the whey depends on the processing treatment used during cheese manufacture, in particular the heat treatment of the milk. In Cottage cheese production, acid cheese whey is produced, which contains undenatured whey proteins, nonprotein nitrogen, lactose, and some salts. In Cream cheese production, the whey separated in the cream separator can contain a higher fat content than cheeses like Quarg (since Quarg is made from skimmed milk). The fat content of the whey can be reduced by reseparating the whey using a standard milk separator. Acid whey is sometimes added back to the separated curd in order to standardize the final moisture content of cream cheese. In the traditional production of Quarg, acid whey is produced as a by-product of centrifugal separation. In the thermoquarg process, where whey is removed using a separator, the liquid stream contains nonprotein nitrogen and non-heat-precipitated whey proteins. When UF is used to dewater the curd, the resulting permeate contains nonprotein nitrogen but no whey proteins. Quarg can also be made from partially concentrated milk (by nanofiltration or UF), followed by acidification, coagulation (as a result of acid production), and UF separation. Acidification of the partially concentrated milk prior to UF helps to reduce the calcium content of the final cheese, which may reduce the possibility of bitterness. The (sweet) permeate produced during concentration of milk is easier to process than acid whey and reduces the
Chandan RC (1991) Cheeses made by direct acidification. In: Robinson RK and Tamime AY (eds.) Feta and Related Varieties, pp. 229–252. Chicester: Ellis Horwood. Farkye NY (2004a) Acid- and acid/rennet-curd cheeses. Part B: Cottage cheese. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 329–341. London: Elsevier Academic Press. Farkye NY (2004b) Acid- and acid/rennet-curd cheeses. Part C: Acidheat coagulated cheeses. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 343–348. London: Elsevier Academic Press. Fox PF, Guinee TP, Cogan TM, and McSweeney PLH (2000) Fundamentals of Cheese Science. Gaithersburg, MD: Aspen Publishers. Guinee TP, Pudja PD, and Farkye NY (1993) Fresh acid-curd cheese varieties. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology – Vol. 1: General Aspects, 2nd edn., pp. 363–419. London: Chapman & Hall. Hindrichs J (2004) Mediterranean milk and milk products. European Journal of Nutrition 43(supplement 1): I/12–I/17. Hui YH (ed.) (2007) Handbook of Food Products Manufacturing. Hoboken, NJ: John Wiley & Sons. Jelen P and Renz-Schauen A (1992) Quarg. In: Hui YH (ed.) Encyclopedia of Food Science and Technology, Vol. 4, pp. 2225–2232. New York: John Wiley & Sons. Kosikowski FV and Mistry VV (1997) Cheese and Fermented Milk Foods, 3rd edn. Great Falls, VA: FV Kosikowski L.L.C. Lucey JA and Singh H (2002) Acid coagulation of milk. In: Fox PF and McSweeney PLH (eds.) Advanced Dairy Chemistry, Vol. 2: Proteins, 2nd edn., pp. 997–1021. New York: Kluwer Publishers. Schulz-Collins D and Senge B (2004) Acid- and acid/rennet-curd cheeses. Part A: Quark, cream cheese and related varieties. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 301–328. London: Elsevier Academic Press. Torres T and Chandan RC (1981) Latin American white cheese – a review. Journal of Dairy Science 64: 552–557.
See also: Enzymes Exogenous to Milk in Dairy Technology: Transglutaminase. Milk Proteins: Casein, Micellar Structure.
Introduction Generally, acid- and acid/heat-coagulated cheeses have a mild or acidic flavor and are usually consumed fresh (i.e., without ripening). These cheeses usually do not have a rind and come in a wide range of shapes and weights. Fresh acid cheeses (sometimes called lactic cheeses) differ from yogurt and fermented milk products in having a significant amount of moisture removed after coagulation by techniques such as centrifugal separation and ultrafiltration (UF), which are used for Quarg and Cream cheeses, or cutting of the coagulum into granules, which is used in Cottage cheese to encourage syneresis. Soft, unripened cheeses, such as Quarg, Cottage, and Cream cheeses, are related in the common use of lactic cultures to form a smooth acid curd. They differ in the method of whey drainage, washing steps, cream incorporation, and type of curd structure. In Cottage cheese, the coagulum is cut to form curd particles of specific sizes, whereas the coagulum for the other acid- and acid/ heat-coagulated cheeses is usually stirred by agitators and the original curd structure is lost. Many fresh cheeses are also blended with fruits, spices, herbs, or other foods. Fat content can be adjusted even after whey drainage in contrast to natural rennet-coagulated cheeses. Some types of natural cheeses, for example, Mozzarella, are sometimes made by direct acidification but usually rennet is used for coagulation. The main processing steps used in the manufacture of fresh acid- and acid/heat-coagulated cheeses are summarized in Figure 1. Traditional equipment for fresh cheese types consists of fermentation vessels, separation equipment, and packaging devices. However, most fresh cheeses are now made by continuous large-scale processes. The legal designations and standards for these fresh cheeses vary from country to country. Most standards are based on the chemical composition of the cheeses (Table 1). Mesophilic lactic acid bacteria (i.e., mainly Lactococcus spp. and Leuconostoc spp.) and sometimes probiotic species are used as cultures for most acid- and acid/heat-coagulated cheeses. In many of these cheeses, diacetyl, lactate, and acetate are important flavor compounds. Incorporation of whey protein into fresh cheese is an important aspect of fresh cheese manufacture because of increased yield. High-heat treatment of milk is not
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usually practiced for Cottage cheese since heating reduces whey syneresis, which causes textural defects, including excessive softness. The shelf life of fresh acidtype cheeses can be reduced by the growth of yeasts and other spoilage organisms, which can grow due to the high moisture content, absence of a surface rind, and a high level of residual lactose.
Mechanism of Coagulation The stability of casein micelles of milk is attributed to their net negative charge and steric repulsion by the flexible macropeptide region of -casein (the so-called ‘hairs’) (see Milk Proteins: Casein, Micellar Structure). Different types of interactions are responsible for micelle integrity, including calcium-induced interactions between protein molecules, electrostatic and hydrophobic interactions, and hydrogen bonding. On acidification, casein particles aggregate as the negative charge repulsion force on caseins is reduced. This leads to the formation of chains, aggregates, and clusters, which eventually form a three-dimensional network. During acidification of milk, the insoluble colloidal calcium phosphate (CCP) present in casein micelles dissolves and this causes the micelles to swell and become more flexible internally. When milk is subjected to preheat treatment, denatured whey proteins associate with casein micelles and they cross-link the gel network when aggregation occurs during subsequent acidification of milk. Heat treatment increases the firmness of milk gels formed by acidification although these gels can be more susceptible to wheying-off as the gel may undergo greater rearrangement. In gels that are formed from preheated milk, gelation occurs at a higher pH (e.g., 5.2–5.4) than that for unheated milk (pH 5.0); these pH values depend on the gelation temperature. The higher gelation pH can be attributed to the higher isoelectric pH (5.2) of the main whey protein, -lactoglobulin, which initiates isoelectric precipitation/aggregation at a higher pH than that observed with caseins, which have an isoelectric point of 4.6. In acid milk gels produced from heated milk, the solubilization of CCP in casein particles that are already part of the gel network can cause a loosening of the gel network, which assists in curd syneresis. At lower pH values, electrostatic interactions are stronger and the gel becomes firmer again and exhibits less syneresis. In
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Standardized milk Quarg cheese production Fat and protein levels Milk treatments: Pasteurization High-heat treatment Homogenization Acidification Direct acid: Types: citric, acetic, lactic, HCl, H3PO4
Starter culture addition: Level: 0.5–5% Temperature: 20–35 °C
Cold milk (Cottage cheese) Hot (80–85 °C) milk (Queso Blanco cheeses) Optional use of rennet: Level: 0.5–15 ml per 1000 l Formation of acid- or acid/heat-coagulated gel Centrifugation/UF Partial removal of moisture Heating Cutting and syneresis (Cottage cheese) Whey Stirring and centrifugation (Quarg and Cream cheeses) UF (Quarg and Cream cheeses) Curd
Permeate
Cold-pack cheese (Quarg, Cottage cheese, Cream cheese)
Further processing of the curd Heat treatment Hydrocolloid addition Homogenization Shearing
Hot-treated curd
Hot-pack cheese (Cream and Neufchatel)
Figure 1 Main processing steps in the manufacture of acid- and acid/heat-coagulated cheeses (dotted lines are optional processing operations). UF, ultrafiltration.
general, conditions such as high incubation temperatures, fast rates of acidification, and preheat treatment of milk encourage greater rearrangements of casein particles in the gel network and the formation of a coarse network. Direct acidification of milk at a low temperature may allow solubilization of CCP prior to gelation and therefore these gels may undergo less changes in their mechanical properties (e.g., syneresis) than traditional cultured products. The addition of rennet results in gelation at a higher pH and the mechanical properties of the curd are changed. Addition of acid to hot milk (as in acid/heatcoagulated cheeses) causes rapid precipitation of casein (and denatured whey protein), and gelation occurs at
higher pH values than with acid coagulation due to the interactions between denatured whey proteins and casein micelles at the high temperature. The high temperature encourages greater collisions (due to increased thermal motion) of particles leading to faster aggregation. Cottage Cheese Introduction
Cottage cheese, sometimes called Pot cheese, is a creamed, acid-coagulated fresh cheese that is low in acidity and is washed during manufacture. Cottage cheese has a slight acid, salty taste with a delicate diacetyl or creamy flavor and aroma. The body of Cottage cheese should be
700 Cheese | Acid- and Acid/Heat Coagulated Cheese Table 1 Approximate composition of various acid- and heat/acid-coagulated cheeses
Variety Cottage Low fat Creamed Cream Double Single Neufchatel Baker’s Quarg Low fat Creamed Fromage frais (skim) Queso Blanco Ricotta High fat Low fat Ricottone Paneer Mascarpone
Moisture (%)
Fat (%)
Protein (%)
Salt (%)
pH
79 79
2 5
14 13
1.0 1.0
4.8–5.0 4.8–5.0
54 70 64 74
33–35 14 20 0.2–0.6
8–10 12 12 19
0.7–1.2 0.7–1.2 0.75 <0.10
4.6–5.0 4.6 4.6 4.4–4.6
82 73 86 48–55
0.5 12 1 15–27
13–15 10 8 19–24
0.1–0.7 0.1–0.7 0.1–1.0 2.3–3.0
4.5 4.6 4.4 5.2–5.7
72 75 73–82 50–55 40–52
13 8 0.5 25–27 45–50
11.5 12 11–19 16–18 2.5–7.5
<0.5 <0.5 <0.5 0.0 0.0
5.8 5.8 4.9 5.4 5.6–6.4
smooth and meaty, and curd particles should be discrete but not soft and pasty. Cottage cheese is popular in the United States (where total production was 360 000 tonnes in 2007), the United Kingdom, and several other countries, and is often used in combination with salads and desserts. Cottage cheese accounts for around 5% of the world’s cheese production. Recent innovations/developments include the addition of probiotic cultures and prebiotics, extension of shelf life through the incorporation of carbon dioxide into the dressing, smaller more convenient single-serve containers, calcium fortification, use of bacteriocinproducing cultures, fruit-flavored products, and the use of UF to increase the total solids (TS) content of the cheese milk. Manufacturing procedures
Cottage cheese is made from pasteurized skimmed milk (in contrast to several other fresh acid cheeses where the milks are often subjected to higher heat treatments). The TS content of the skim milk is often increased to 10–13% by fortification with nonfat dry milk powder (NFDM;
skim milk powder) or by the addition of UF retentate. There are at least three different procedures for the manufacture of Cottage cheese based on the length of the setting time prior to cutting: long-, medium-, and short-set methods (Table 2). The length of time before cutting varies from 5 to 16 h and the temperature of setting ranges from 22 to 35 C. A higher level of starter inoculum and high incubation temperature are used in the short-set method compared with the slow long-set method. Non-gas-producing mesophilic cultures (e.g., Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris) are usually used. Recently, in the United States, there has been a trend away from bulk starter and towards direct vat inoculants. A low level of rennet (1–3 ml per 1000 l milk) may be added, which helps to form a suitable gel after a shorter incubation period. Rennet is often added after some acidity has developed by the starter culture (e.g., after 1–2 h). When rennet is added, the gel is ready to be cut at a higher pH (e.g., 4.75) than in its absence (e.g., 4.6). After cutting, the curd is left undisturbed for 15–35 min. Curds of different sizes are produced by cutting the coagulum
Table 2 Some of the processing conditions commonly used for the production of Cottage cheese Process step
Short set
Medium set
Long set
Rate of starter addition (%) Conventional bulk starter pH-controlled starters Time before cutting (h) Incubation temperature ( C)
5 2 5 30–33
2 1 8 27
1 0.5 12–16 21–24
Cheese | Acid- and Acid/Heat Coagulated Cheese
with different-sized knives. After this resting period, the curds are cooked slowly with gentle stirring for 1–3 h until a temperature between 47 and 56 C is reached. Cottage cheese curd is fragile and shattering occurs if the curd is mishandled. When the same vat is used for the complete production operation, the curds are normally washed three times with water at a decreasing temperature, for example, 28–22, 16–10, and 5–2 C. Washing removes lactose and lactic acid, and cools the curd to slow down further acid production and syneresis. The total time for washing and drainage steps is 3 h. After all the water has been drained off, pasteurized cream (10–20% fat) at 4 C containing a small amount of salt and stabilizers (e.g., xanthan gum, carrageenan, and/or guar gum), known as ‘dressing’, is added and mixed into the curd. In the United States, creamed Cottage cheese contains 79% moisture, 16% solids nonfat, 4% fat, and 1% salt. After a short holding time, the curds are packed into containers (e.g., vacuum-formed polystyrene tubs with a shrink film of polypropylene) and stored at 4–5 C for retail distribution and they have a typical shelf life of up to 3–4 weeks (in the United States). Cottage cheese can also be made by direct acidification of cold milk (4 C) to pH 5.2–4.7. Milk is usually acidified to pH 5.1 with hydrochloric, phosphoric, lactic, or other acids and then warmed to a higher temperature, for example, 32 C, when a small amount of the acidogen, gluconic acid--lactone (GDL), is added to the milk to reduce the pH of milk to 4.7. The milk then coagulates and the curd is treated as normal. Using this approach, slow acidification of milk can be achieved, whereas addition of a high concentration of GDL at a high temperature would cause a rapid reduction in milk pH. Equipment
Most Cottage cheese is made in rectangular, open vats but the whey draining, curd washing/cooling, and creaming steps may be performed in separate equipment, which improves process efficiency (e.g., reduces water usage). The main processing equipment for Cottage cheese includes plate heat exchangers (to pasteurize the milk), milk fermentation tanks, cutting devices, stirring area with indirect or direct heating, whey drainage belts with curd washing stations/tanks, pressing belt, area for addition of dressing (in vats or by mixers), and a packaging/ filling system. Several types of heating systems are used, including drawing whey from the top of the vat and passing it through a heat exchanger and ‘jet cooking’, which is similar to the previous system except that culinary steam is injected into the whey. Uniform heating is critical to prevent ‘burn-on’ during the cooking stage. Gentle agitation is required as the curd is fragile; several agitator designs have been developed including vertical stirring motion (e.g., the Vert-Stir from Stoelting) to minimize damage.
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Defects
Minor sludge formation is a defect that can occur during Cottage cheese manufacture. This ‘sludge’ is caused by agglutination of starter bacteria and milk proteins, which can occur during the incubation period. Homogenization of the skim milk and careful selection of starter cultures are two methods commonly used to reduce the likelihood of this defect occurring. A ‘floating curd’ defect can also occur during cooking of Cottage cheese curd and is usually attributed to cultures (e.g., citrate-positive strains of Lc. lactis) that may produce excessive amounts of carbon dioxide. Careful selection of starter cultures for both acid- and flavor-producing ability is necessary. The defect called ‘major sludge formation’, where all the curd seems to form a sludge at the bottom of the vat, is usually thought to be due to phage infection of the vat during fermentation. In contrast to most other fresh cheeses, Cottage cheese has a granular, curdy texture rather than a viscous, smooth, or pasty body. Sorbates and other preservatives are often used to increase shelf life. Another approach to increase shelf life is injection of carbon dioxide (about 600–1100 mg kg 1), which is injected directly in the cream line. Carbonated cream enters the cream/curd mixer and the product is barrier packaged. The increase in shelf life (up to 8 weeks) depends on the amount of carbon dioxide initially dissolved in the product and the barrier properties of the packaging system during storage.
Cream Cheese Introduction
Cream cheese includes several closely related products including single Cream cheese, double Cream cheese, Neufchaˆtel (spelled Neufchatel in the United States), and Bakers’ cheese. In Germany, Rahmfrischka¨se (rahm means cream in German) is a type of single Cream cheese, while Doppelrahmfrischka¨se is a type of double Cream cheese. Cheeses that are closely related to Cream cheese are produced in other countries, for example, PetitSuisse, Gournay, Bondard, Fromage a la Cre`me, and Carre´ Frais (carre´ meaning ‘square’) in France (some of these cheeses have a white surface mold). In the US standards of identity, Cream cheese must contain a minimum of 33% fat and a maximum of 55% moisture. Cream cheese is very popular in the United States, with total production of Cream and Neufchatel in 2007 around 350 000 tonnes. Cream cheese was first made in the United States in 1872. Cream cheese is used on bagels, in salads, and as an ingredient in flavored spreads, frostings, and cheesecake. In some countries, a Cream cheesetype product is made by combining a Quarg-like curd with cream or butter. Imitation cream cheese involves substitution of some or all the milk fat with vegetable fats.
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Neufchatel cheese must contain 20% but <33% fat and a maximum of 65% moisture. Bakers’ cheese is produced in the United States and is widely used in the bakery and confectionary trades, hence its name. It is made from skim milk and has a soft, dry, grainy, pliable curd. Neufchatel cheese is made from milk with 5% fat but otherwise by a procedure similar to that of Cream cheese; owing to its lower fat content, it has a grainier body and is less smooth than Cream cheese. The traditional French version of Neufchaˆtel may be made from whole raw milk that is heated to around 20–30 C, at which point a small quantity of rennet is added and the milk allowed to coagulate for 1–1.5 days. During this coagulation period, the milk sours due to its adventitious microflora. The curd is hung in cloth bags to drain for half a day, after which pieces of mature Neufchaˆtel are added and the curd put into molds and covered and salted. The curd is allowed to age for about 10 days, although it can be aged longer. The rinds develop a white surface mold. Recent innovations in Cream cheese include nonstandard of identity (United States) products that are designed to be more spreadable, whipped cream cheese, bagels with cream cheese in one container, wheyless cream cheese made with transglutaminase (see Enzymes Exogenous to Milk in Dairy Technology: Transglutaminase), and shelf-stable cream cheeses (processed cream cheese). Manufacturing procedures
Single (fat) Cream cheese is made from milk with a fat content of 3–3.5%, while double Cream cheese is made from milk containing 8–14% fat. Industrially, there is trend of using higher TS in cheese milks to help reduce the amount of (acid) whey that would be needed to be removed from curd during cheesemaking. Milk is standardized and homogenized (e.g., 12–17 MPa at 50 C) and cooled to 31 C for a short-set (incubation time 5 h) and 22 C for a long-set (incubation time 12–16 h) procedure. Then, the starter is added (e.g., 2%), the level of which depends on the incubation period and temperature. At the end of incubation, the pH is 4.7–4.8. In some processes, a small amount of rennet may be added (e.g., 5 ml of standard rennet per 1000 l milk) with the starter, but is not essential. The gel is broken using agitators and heated to 40–55 C (to encourage syneresis and efficient separation), when whey is separated from the curd using either a Cream cheese separator or UF (operating temperature is usually 50–55 C to reduce viscosity while concentrating). Traditionally, whey was drained using cloth bags. There are two main product types, cold-pack and hotpack products. In the manufacture of cold-pack Cream cheese, after whey separation, the cold curd (10–12 C) is salted, stabilizers are added, and the product is packaged. Typically, around 0.3% of a single stabilizer or combination of several stabilizers, such as locust bean
gum, guar gum, xanthan gum, and carrageenan, is added. Stabilizers are added to help prevent syneresis and the appearance of free moisture on the surface of the product during storage. In some Cream cheese products, whey protein concentrates are also added as a stabilizer. In the hot-pack process, the curd is mixed with salt and stabilizers in kettles or scraped-surface heated vats and heated to 65–70 C. The hot curd (65–70 C) is then pumped into packages and subsequently allowed to cool. The curd is sometimes heated to temperatures as high as 80 C to aid mechanical separation of whey and this further heat treatment of the curd may be carried out in a tubular heater. Instead of a tubular heater, the hot (70–75 C) product may be homogenized at 12–15 MPa. Cream cheese is also made by direct acidification (using organic acids) of milk.
Equipment
Essential equipment for cold-pack Cream cheese and (United States) Neufchatel includes basic mix pasteurizing vats, homogenizer, plate surface or tubular heat exchangers, fermentation vats, balance tanks, mechanical separator or UF unit, centrifugal and positive displacement pumps, fillers, blenders, and packaging lines. Tubular heat exchangers are often used to cool the viscous cheese for cold-pack products. For hot-pack Cream cheese, large jacketed vats with agitators or a scrapedsurface heat exchanger and an additional homogenizer for the hot mix are also required. Double Cream cheese separators have a design different from that of Quarg separators because the higher fat content results in ejection of the whey (being heavier) toward the bowl wall, and ejection of the cheese product toward the center.
Texture and defects
If the pH of the cheese is too high (i.e., >4.7), the texture will be soft and the cheese will lack flavor. At a very low pH (<4.6), the texture may become too grainy and the flavor too acidic. Defects in these cheeses include whey separation from the product during storage and a grainy chalky texture, especially in the lower fat types. Hotpack cheese has a more brittle texture than the coldpack product due to the additional heating and shearing treatments. Cream cheese should be spreadable as it is commonly used on bagels and in cheesecakes. Cream cheese is often sold in plastic tubs, in cartons, or wrapped in metal foil, and is often blended with various flavors, herbs, and spices. The shelf life of the cold-pack product is only a few weeks, whereas the hotpack cheese has a shelf life of up to 3 months on refrigerated storage. Improperly stored or packaged Cream cheese can undergo lipid oxidation, which can limit its shelf life.
Cheese | Acid- and Acid/Heat Coagulated Cheese
Quarg Introduction
Quarg (Quark) is another fresh cheese that is often mixed with cream, fruit, or seasonings. Quarg is a smooth, soft, spreadable paste, which is used in many home-prepared foods and dishes. This cheese is popular in central Europe (e.g., Germany, Poland, and Austria). Other names for this type of product in different countries include Kvarg, Tvarog, Tworog, Twarog, Sauermilchquark, and Speisequark. Chakka, a product related to Quarg, is popular in India; it is a fermented curd formed by acid coagulation of milk at 28–30 C and drainage of whey using muslin bags. Shrikhand (also spelled Srikhand) is a fresh cheese made in India by mixing sugar and spices to Chakka. Fromage frais (fresh cheese) is a cheese related to Quarg and is produced in France and some other European countries. Fromage frais products are produced with a range of fat contents and are often blended with fruits. These cheeses are marketed as chilled (dairy) desserts. Similar products are produced in other parts of the world. In Germany, several cheeses (e.g., Harzer, Mainzer, and Handkaese) are made from an acid curd (Quarg-like) product by allowing a surface flora (smear) to develop and therefore this type of cheese undergoes ripening. Manufacturing procedures
The dry matter content of nonfat Quarg varies from 14 to 24%; for example, in Germany, the minimum TS and protein contents of soft cheese are 18 and 12%, respectively. The protein content of nonfat Quarg varies from 12 to 18%. The higher levels of solids are harder to achieve using UF or a Quarg separator than by the traditional process. Traditional Quarg was separated from whey using filter cloths or muslin bags (i.e., in batches). Quarg-like products with many different fat contents are manufactured in European countries. In the traditional manufacture of Quarg, the milk is pasteurized just before fermentation. However, severe heat treatment of milk, which denatures whey proteins, is now commonly used in the manufacture of Quarg. There are two main processes for the manufacture of Quarg, thermoquarg and UF Quarg. In the thermoquarg process, milk is subjected to a high-temperature–long-time pasteurization at 85–95 C for 3–15 min (using a long tubular holding section in the heat exchanger) and further treatment (56–60 C for up to 3 min) of the acidified milk before cooling to 40 C for centrifugal separation. Both heat treatments are considered to give a higher yield (10%) because of the incorporation of denatured whey proteins. In the Centriwhey and Lactal processes, Quarg whey is heat-treated (e.g., 95 C) and concentrated (these two methods differ in the TS content of the denatured whey product), and the denatured
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protein is then added back to cheese milk used to make the next batch of Quarg. This process is used to alter the texture and increase cheese yield. The main difference between thermoquarg and UF Quarg processes is that whey is separated by UF in UF Quarg. After heat treatment, milk is cooled to 20–28 C and a starter culture (Lc. lactis subsp. lactis, Lc. lactis subsp. cremoris and/or Leuconostoc spp. and citrate-positive strains of Lc. lactis) is added (0.3–4%) together with a small amount of rennet. The level of rennet added is usually about 10% of that used in the manufacture of rennet-coagulated cheese, that is, 5–15 ml standard rennet per 1000 l milk. Often, some acidity (e.g., pH 6.3) is allowed to develop (e.g., 60–90 min after the addition of starter cultures) before rennet is added. This gives a firmer coagulum in high-heat-treated milk. After 16 h, when the gel is at pH 4.6, the coagulum is stirred. In a short-set method, a temperature of 27–30 C is used and the incubation time is 5–6 h. The mix is then heated (e.g., 60 C for 1–6 min) and separated using either a Quarg (centrifugal) separator (operating temperature 32–44 C) or UF membranes (operating temperature 40–45 C), both working in a continuous mode. If the Quarg is creamed, an appropriate amount of sweet or cultured cream is added prior to packaging. The shelf life is usually 2–4 weeks with refrigerated storage. For a long-life Quarg, the final product is heat-treated, which helps to reduce bacterial numbers. Suitable stabilizers are added to a buffer tank after separation and prior to final heating.
Equipment
A Quarg production line is similar to that for Cream cheese and contains fermentation tanks, plate heat exchangers, Quarg separator/UF unit, positive displacement pumps, plate coolers, creaming tank or mixer (if fat is added), and a filling/packaging system. Quarg separators are somewhat similar to cream separators but the bottom part of the bowl is equipped with nozzles through which curd is discharged continuously.
General properties
Quarg from skim milk is smooth and white with a mild clean, acid flavor. Addition of cream gives extra flavor and smoothness. Excessively high calcium and rennet levels are considered to be associated with a ‘bitter’ taste defect. Quarg can also be made using partially concentrated milk, followed by acidification, coagulation, and UF separation. Acidification of the partially concentrated milk prior to UF helps to reduce the calcium content of the final cheese. Gelatin or other hydrocolloids are sometimes added to Quarg as stabilizers.
704 Cheese | Acid- and Acid/Heat Coagulated Cheese
Acid/Heat-Coagulated Cheeses Queso Blanco or Hispanic Cheeses Several types of fresh acid/heat-coagulated cheeses are made in Latin American countries under the general name Queso Blanco (also called Hispanic or white cheeses). Many types of Queso Blanco cheeses, for example, Queso Fresco, Queso de Prensa, Queso de Puna, Queso de Hoja, Llanero, and Quesillo, are usually coagulated with rennet. The manufacturing procedure (e.g., the use of rennet or acid/heat to coagulate the milk) for Queso Blanco cheeses can vary from country to country and also from the traditional (farm) process to that used in modern factories. The acid/heat-coagulated Queso Blanco cheeses (such as Queso del Pais, Queso de la Tierra, and Queso Sierra) are usually made from skimmed, partially skimmed, or whole milk that is pasteurized at 80–85 C. Acidulants (e.g., acetic, lactic, or citric acid) are added to the hot milk to bring the pH to 5.0–5.4 and then stirred, dewheyed, and salt and flavors added. The mixture is then pressed, packaged, and stored. In traditional methods for the production of these types of cheese, the milk is acidified by the addition of vinegar, lemon juice, or other fruit juices that are available locally. For some cheeses, after curd has been precipitated and cooled to 32 C, a lactic starter culture (mainly Lactobacillus spp.) may be added to give additional flavor to the cheese; the cheese is then packaged as usual.
5.4 with citric acid and heated to 80 C to recover additional whey proteins and is used to make Ricottone cheese (sometimes whole milk is added to the whey). In a recently developed continuous Ricotta process, blends of full-fat milk and whey are heated to 90 C and directly acidified with acid to pH 5.3–5.5, which results in precipitation of the protein. The curd is then separated from the whey on a conveyor belt and hot packaged. Ricotta is often used in baking and confectionary applications. Requeso´n is a spreadable Hispanic cheese that is similar to Ricotta.
Mascarpone Mascarpone is a traditional soft Italian cheese that is made from hot (85–90 C) cream (e.g., 25–35% fat) that is acidified with acid (e.g., acetic, citric, or tartaric acid) to pH 5.7–6.4. The curd formed is drained in cloth bags (for long periods, e.g., 20 h), mixed or whipped, and packaged. The cheese is consumed fresh (unsalted or lightly salted) and it is pale or cream-colored, with a mild creamy (slightly tangy) flavor and a thick, spreadable consistency. This cheese is often used in cakes or to make desserts (e.g., Tiramisu). Membrane filtration or separation has replaced the cloth bags. Recently, higher fat creams have been used in conjunction with UF and hot filling in order to speed up the long curd drainage time required with the traditional process; this process also increases yield and improves shelf life (up to 45 days at temperatures 4 C).
Ricotta and Ricottone Cheeses Ricotta cheese was traditionally made in Italy from the whey from sheep’s milk cheese, which was heated to denature and coagulate the whey proteins; the coagulated protein was scooped from the whey. The traditional process has been modified in some countries due to the increasing popularity of Ricotta, which is now often made from milk or milk/whey mixtures. Dried whey protein powders have also been used in the manufacture of Ricotta. In the traditional (batch) process, whey (or milk/whey mixtures) is acidified to pH 5.6–6.0 with starter culture or acid (e.g., acetic or citric acid) and heated to 80 C by stream injection or by indirect heating of the vats. The flocculated protein rises to the surface where it is collected and separated from the whey and placed in molds for further drainage. Calcium chloride is sometimes added to improve flocculation. The curd may be homogenized to produce a smoother consistency. UF is now often used to concentrate the whey (or milk/whey mixtures) prior to or after acidification and the retentate is concentrated to 30% TS. The UF retentate is then heated and hot packaged. Acidification can also be carried out by the addition of acid whey powder to milk. The whey derived from Ricotta cheese can be acidified to pH
Paneer Paneer, another acid/heat-coagulated cheese, is popular in India and the Middle East. It is made from cows’ or buffaloes’ milk. The milk is heated to 85–90 C, cooled slightly (e.g., to 72 C), and lemon juice, citric acid, or sour whey is added to coagulate the milk (which usually takes only a few minutes). Sometimes a small quantity of calcium chloride is added to the hot milk to aid coagulation. The coagulated milk is stirred gently and the curds are separated from the whey by straining through cheese cloth. The curds are placed in hoops and lightly pressed, cooled using chilled water, packaged, and stored (usually no salt is added). The moisture content of the cheese is typically 50–55% and the pH is 5.4. In India, the regulations for Paneer indicate that it should not contain more than 70% moisture and the milk fat content should not be less than 50% of the dry matter. Versions of this cheese are made in India by different methods, including using rennet to coagulate the milk (e.g., Panir), allowing milk to sour naturally before heating, or adding sour buttermilk to freshly boiled milk. Chhanna or Channa (which is also produced in India) is very similar to
Cheese | Acid- and Acid/Heat Coagulated Cheese
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Paneer cheese except that the curd is not pressed. In India, the regulations for Chhana indicate that it should not contain more than 70% moisture and milk fat should not be less than 50% of the dry matter. The shelf life is usually no more than about 6 days with refrigerated storage.
volume of acid whey produced during curd/whey separation.
Derived Products
Further Reading
Acid whey is the major by-product from acid- and acid/ heat-coagulated cheeses. The composition of the whey depends on the processing treatment used during cheese manufacture, in particular the heat treatment of the milk. In Cottage cheese production, acid cheese whey is produced, which contains undenatured whey proteins, nonprotein nitrogen, lactose, and some salts. In Cream cheese production, the whey separated in the cream separator can contain a higher fat content than cheeses like Quarg (since Quarg is made from skimmed milk). The fat content of the whey can be reduced by reseparating the whey using a standard milk separator. Acid whey is sometimes added back to the separated curd in order to standardize the final moisture content of cream cheese. In the traditional production of Quarg, acid whey is produced as a by-product of centrifugal separation. In the thermoquarg process, where whey is removed using a separator, the liquid stream contains nonprotein nitrogen and non-heat-precipitated whey proteins. When UF is used to dewater the curd, the resulting permeate contains nonprotein nitrogen but no whey proteins. Quarg can also be made from partially concentrated milk (by nanofiltration or UF), followed by acidification, coagulation (as a result of acid production), and UF separation. Acidification of the partially concentrated milk prior to UF helps to reduce the calcium content of the final cheese, which may reduce the possibility of bitterness. The (sweet) permeate produced during concentration of milk is easier to process than acid whey and reduces the
Chandan RC (1991) Cheeses made by direct acidification. In: Robinson RK and Tamime AY (eds.) Feta and Related Varieties, pp. 229–252. Chicester: Ellis Horwood. Farkye NY (2004a) Acid- and acid/rennet-curd cheeses. Part B: Cottage cheese. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 329–341. London: Elsevier Academic Press. Farkye NY (2004b) Acid- and acid/rennet-curd cheeses. Part C: Acidheat coagulated cheeses. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 343–348. London: Elsevier Academic Press. Fox PF, Guinee TP, Cogan TM, and McSweeney PLH (2000) Fundamentals of Cheese Science. Gaithersburg, MD: Aspen Publishers. Guinee TP, Pudja PD, and Farkye NY (1993) Fresh acid-curd cheese varieties. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology – Vol. 1: General Aspects, 2nd edn., pp. 363–419. London: Chapman & Hall. Hindrichs J (2004) Mediterranean milk and milk products. European Journal of Nutrition 43(supplement 1): I/12–I/17. Hui YH (ed.) (2007) Handbook of Food Products Manufacturing. Hoboken, NJ: John Wiley & Sons. Jelen P and Renz-Schauen A (1992) Quarg. In: Hui YH (ed.) Encyclopedia of Food Science and Technology, Vol. 4, pp. 2225–2232. New York: John Wiley & Sons. Kosikowski FV and Mistry VV (1997) Cheese and Fermented Milk Foods, 3rd edn. Great Falls, VA: FV Kosikowski L.L.C. Lucey JA and Singh H (2002) Acid coagulation of milk. In: Fox PF and McSweeney PLH (eds.) Advanced Dairy Chemistry, Vol. 2: Proteins, 2nd edn., pp. 997–1021. New York: Kluwer Publishers. Schulz-Collins D and Senge B (2004) Acid- and acid/rennet-curd cheeses. Part A: Quark, cream cheese and related varieties. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn., pp. 301–328. London: Elsevier Academic Press. Torres T and Chandan RC (1981) Latin American white cheese – a review. Journal of Dairy Science 64: 552–557.
See also: Enzymes Exogenous to Milk in Dairy Technology: Transglutaminase. Milk Proteins: Casein, Micellar Structure.