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Cream | Products
Products W Hoffmann, Max Rubner-Institut, Kiel, Germany ª 2011 Elsevier Ltd. All rights reserved.
Introduction Cream is a comparatively rich emulsion of milk fat. Cream and cream products are sold in many varieties. In most countries, there exist traditional classes of cream products, mostly divided according to the fat content. However, no uniform legal definition and classification has gained worldwide acceptance. The fat content of the different liquid and cultured products ranges from 10 to 50%. Often, subclasses are used. Coffee, half, light, and single cream usually have a fat content of 10–30%, whipping cream has a fat content of 30–40%, and double cream 45–50%. Cream products are also classified according to their thermal treatment. Minimum pasteurization is the best way to preserve cream flavor; however, increasingly, in several countries, more severe heat treatments are practiced for the convenience of extended shelf life at ambient temperatures. Whereas in-bottle sterilization has become less common, ultra-high temperature (UHT) heating and pasteurization with temperatures well above 100 C have gained ground. Nowadays, products such as coffee cream are predominantly flow-sterilized. Cultured or sour creams hold a special position within the range of cream products, because they belong to a diverse group of fermented products. Hence, regulations and manufacturing processes have been adopted from this group. Cream is also used as an essential ingredient in other dairy or nondairy products such as ice cream and cream liqueur (see Cream: Manufacture). In addition, cream is the primary product in the manufacturing process of butter and butter oil (see Butter and Other Milk Fat Products: The Product and Its Manufacture). Some cream products may even be directly used as spreads.
Types and Regulations Cream and cream products have a variety of compositions and are normally defined according to fat content and, sometimes, also by function or heat treatment. Until now, the traditional classes of cream products in different countries have not been made uniform. In 1977, the Food and Agriculture Organization (FAO) and World Health Organization (WHO) suggested
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standards for nonfermented market cream combining fat content and function. Half cream should have a fat content 10 and <18%, cream 18%, whipping cream 28%, heavy whipping cream 35%, even though higher fat creams are less dense and thus lighter per unit volume, and double cream 45%. However, these suggestions did not prevail over national legislation. A new initiative was taken by the Codex Alimentarius Milk Commission and the International Dairy Federation (IDF). The revised ‘Codex Standard for Cream and Cream Products’ (2003) describes cream as ‘‘. . . the fluid milk product comparatively rich in fat, in the form of an emulsion of fat-in-skimmed milk, obtained by physical separation from milk. Prepared creams are the milk products obtained by subjecting cream . . . to suitable treatments and processes to obtain the characteristic properties as specified below.’’ These prepared creams comprise prepackaged liquid cream, whipping and whipped cream, cream packed under pressure (aerosol whipping cream), fermented cream, and acidified cream. The minimum fat content of all these creams has to be 10%. National regulations make more distinctions regarding fat content. Products with a low fat content are German ‘coffee cream’ (10% fat), ‘half-and-half cream’ (10.5% fat) in the United States, and British ‘half cream’ (12% fat). Traditional (whipping) cream contains 30% fat in Germany and the Netherlands, whereas the same product contains 35% fat in the United Kingdom, Australia, and New Zealand. The US Food and Drug Administration makes a distinction between ‘light whipping cream’ (30% fat) and ‘heavy whipping cream’ (36% fat). Applied heat treatments for the different cream products include pasteurization, UHT heating (135 C), flow sterilization in a UHT plant (<135 C), and in-bottle sterilization (see Heat Treatment of Milk: Sterilization of Milk and Other Products; Ultra-High Temperature Treatment (UHT): Aseptic Packaging. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk). Cultured or sour creams are regulated as are fermented products. Their fat content also ranges from 10 to more than 40%. In the United Kingdom and the United States, a minimum fat content of 18% is required. In countries such as France, Germany, Denmark, and Sweden, the term ‘cre`me fraıˆche’ has a different definition in each nation’s legislation. ‘Smetana’ is a popular sour cream product in eastern Europe and Finland. In the
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United States, the addition of ‘acidified’ to the name means that the cream is soured with safe and suitable acidifiers such as gluconic acid--lactone, with or without the addition of lactic acid bacteria. The manufacturing processes of cultured creams are largely similar to those of other fermented products (see Fermented Milks: Yoghurt: Types and Manufacture). ‘Clotted cream’ (55% fat) is a product that is virtually unique to South West England and is used for tea and dessert (with scones and jam). A thin layer of cream is heated at about 80 C for 1 h (scalding), resulting in a cream crust and a rich, sweet flavor. Similar products are ‘o¨rom’ (Mongolia), ‘malai’ (India), and ‘kaymak’ (Near and Middle East). Cream liqueurs, which contain an essential amount of cream, are normally regulated as are spirits. In a cream liqueur produced in the European Union, 15% of cream with 10% fat is required. Removal of water from cream by spray-drying yields cream powders with an extended shelf life if antioxidants are added and adequate storage conditions are guaranteed. To obtain functional products after reconstitution, incorporation of emulsifiers, such as monoacylglycerols, is necessary. Legally, cream powders normally belong to the group of dry milk products (see Dehydrated Dairy Products: Milk Powder: Types and Manufacture). There are many more products with the word ‘cream’ in their designation. Well-known examples are ice cream, cream cheeses, and cream spreads (see Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Milk Fat-Based Spreads. Cream: Manufacture. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Product Types). During the manufacturing process of liquid cream products, certain substances can be added if legally permitted. Typically, coffee cream contains stabilizing salts such as phosphates and citrates, and the creaming of whipping cream within the package is delayed by carrageenan, which also reduces syneresis after whipping. Cream liqueurs are stabilized by citrate, whereas cultured cream products are usually processed without adding hydrocolloids. In the European Union, the legal regulations concerning additives have been uniform for some years. The permitted substances in liquid cream comprise phosphoric acid and mono-, di-, tri-, and polyphosphates, lactic acid and lactates, citric acid and citrates, chlorides, alginic acid and alginates, agar-agar, carrageenan, xanthan gum, pectins, cellulose and cellulose derivates, starch derivates, emulsifiers (lecithin and mono- and diacylglycerols of edible fatty acids), and the propellants carbon dioxide, nitrogen, or dinitrogen monoxide in whipped creams. Not all of the additives on this extensive list are, however, really helpful or necessary for the production of high-quality cream products, and hence not all are used.
Quality Problems Coffee Cream In many countries, coffee cream is a popular product, which is manufactured for long storage either by in-bottle sterilization or by flow sterilization in a UHT plant. It competes with evaporated milk, liquid or foamed whole milk, and liquid or dried coffee whiteners, which often contain vegetable fats. After opening of a briefly shaken cream package, the consumer expects good sensory properties of the content and that the ingredients, that is, fat and protein, have remained in a homogeneously dispersed state. In a hot coffee beverage, a high whitening effect as well as a high coffee stability is demanded. Coffee stability, which is of outstanding importance for the quality of this product, means the degree of resistance against coagulation or ‘feathering’. Creaming or sedimentation phenomena during storage depend on the fat content of cream and on the conditions of heat treatment and homogenization during the manufacturing process (see Cream: Manufacture). It is obvious that creaming problems increase with the fat content. The fat content is limited to about 20% to obtain a desirable homogenization effect (volume-moment average diameter 0.4–0.6 mm, nearly identical size) because casein is partly bound to the fat as a major constituent of the newly formed fat globule membrane. The considerable enlargement of the total fat globule surface after homogenization as a result of the increased globule numbers and its reduced diameter requires a sufficient amount of casein, that is, a sufficiently high protein/fat ratio. The more the available casein is adsorbed on the fat globules, the more the aggregation of fat/protein complexes is favored (due to the higher sensitivity to changes in electrical charge). A thermally induced aggregation may occur during in–bottle or flow sterilization of the coffee cream. Its extent depends more on the heating temperature than on the heating time. That is why flow sterilization is carried out preferably with temperatures below 130 C. In addition, the process of flow sterilization in a UHT plant allows a second two-stage homogenization after heating in order to split up aggregates (clusters) formed. A resulting coffee cream with predominantly nonaggregated fat globules shows a low viscosity, which is a desirable characteristic. The aggregation of fat/protein complexes in hot coffee solutions is affected by the manufacturing process of the cream, but also by coffee brand, water ingredients, brewing conditions, actual temperature, and other factors. Most coffee solutions have pH values of about 5.0, which is near the isoelectric point of casein. In combination with high temperatures and low or very high water hardness, coagulation and aggregation can easily occur. When the temperature of a cold coffee solution with dispersed cream increases, the growing aggregates remain
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invisible to the naked eye until they have a sufficient size. At this temperature, feathering becomes perceptible and the whitening power of the cream decreases at the same time. After pouring the coffee cream from a small polystyrene (PS) package into a coffee solution, clearly defined large white floccules can float on the surface, and this is not a result of feathering. These floccules are dried particles from inside the package that were formed during storage because PS permits substantial water vapor permeability (see Packaging).
Whipping Cream The whipping of a traditionally pasteurized, continuously and sufficiently cooled cream with a fat content of not less than 30% is unproblematic if a raw milk of good quality is used and the production of cream continues largely without mechanical stress. Each additional percent of fat up to 40% reduces whipping time and results in a firmer foam. Quality defects of raw milk, nonoptimal processing, a lower fat content, and, most of all, the demand for a prolongation of shelf life generally cause problems. Raw milk contains enzymes with different activities and some of them are responsible for the development of specific flavor compounds and defects in milk and cream. The native milk lipase, for example, is lipoprotein lipase (LPL) that catalyzes the hydrolysis of triacylglycerols to free fatty acids. The activity of LPL is theoretically sufficient to cause rancidity in less than 1 min. However, liberation of free fatty acids is prevented by an intact milk fat globule membrane. Since the fat globule membrane protects milk fat against lipolysis, the milk must be carefully handled to minimize damage to the fat globule membrane. Homogenization of cream produces a greatly enlarged area of milk fat covered with a new membrane. This milk fat is vulnerable to the action of LPL, and subsequent rancidity occurs if no immediate pasteurization inactivates this heat-labile enzyme. Lipolytic rancidity is also induced by extracellular bacterial lipases of Pseudomonas spp. and other Gram-negative psychrotrophs. In many cases, these lipases are not inactivated by pasteurization and may even be present in UHT cream (e.g., lipases of Pseudomonas fluorescens). Extracellular proteinases of Gram-negative psychrotrophs may be also very heat-stable and can show activity even after in-bottle sterilization of cream. Phospholipases, proteinases, and glycosidasas from psychrotrophic Pseudomonas, Citrobacter, and Enterobacter may act synergistically in damaging the fat globule membrane. The aggregation of fat globules, which produces bitty cream, has been linked to the specific activity of phospholipase from Bacillus cereus. Psychrotrophic spore formers in raw milk such as Bacillus spp., which cause sweet coagulation, can survive pasteurization, and also
heat-resistant spores may occur in UHT cream (see Enzymes Indigenous to Milk: Lipases and Esterases. Psychrotrophic Bacteria: Pseudomonas spp.). The prolonged shelf life of UHT cream means that high demands are made on filling and packaging materials. In contrast to pasteurized cream, the UHT product must be aseptically filled and packed. Therefore, the filling equipment and packaging materials have to be tolerant to water, steam, hydrogen peroxide, heat, and UV light. Whether the whipping cream is pasteurized or UHT heated, there are some common important factors that must be taken into consideration. Light and/or oxygen may induce oxidation of unsaturated fatty acids, leading to flavor degradation. The appropriate filling conditions should be selected to minimize the oxygen content in the package (with small headspace volume) and in the cream (see Packaging). Homogenized cream is particularly susceptible to the action of light. The sensitivity of cream to light depends also on the heating conditions. UHT heating causes sulfhydryl groups and hydrogen sulfide to be released from -lactoglobulin, initially creating an intense cooked flavor (see Heat Treatment of Milk: Ultra-High Temperature Treatment (UHT): Aseptic Packaging; Ultra-High Temperature Treatment (UHT): Heating Systems). During storage, oxidation of these groups causes the cooked flavor to disappear and the strong reducing activity inhibits the development of off-flavor compared with those likely to occur in pasteurized cream. A balanced antioxidative/oxidative action of sulfhydryl groups and oxygen will probably help to ensure cream products of a good sensory quality. But even if well-balanced conditions can be maintained, light transmission must be kept at a low level. UHT whipping cream is expected to have a shelf life of about 3 months. But particularly during the summer period, consumers complain about quality defects. A short-lived warming up of a cream package to a temperature of 30–35 C, as may occur during transport without cooling, produces adverse effects after slow recooling. It not only supports creaming during subsequent storage at 20 C, but may also lead to a distinct thickening after cooling before whipping. Although not all the fat is melted after the warming up, this ‘rebodying’ is caused by increased size of fat crystals during recooling. This results in partial coalescence without stirring provided that the fat content is so high that the fat globules are very close together. A continuous storage temperature of 5 C delays creaming and the occurrence of sensory problems when compared to storage at 20 C. The whipping time of the cream is extended as a result of cold storage, but it also results in an increased volume. Whenever comparative studies or assessments of whipping properties are carried out, standardized temperature and whipping conditions must be ensured, for
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which special regulations exist in many countries. Usually, whipping time and overrun, and firmness and leakage of the foam are measured. Most devices used to test whipping are modifications of the one originally described by Mohr and Baur in 1937. It consists of two hexagonal, cylindrically arranged wire baskets rotating at a constant speed. The cream, which is stored for 24 h at 4 C, is whipped in standardized cooled (5 C) cups until there is no appreciable increase in the load required to turn the blades. Percent overrun is calculated as the volume difference after and before whipping, divided by the volume of unwhipped cream and multiplied by 100. An overrun of not less than 80% is desirable. Firmness can be equated with the length of time needed by a standardized plunger to penetrate the foam to a defined depth. When using a texture analyzer, the average force required to move the plunger at a constant speed within the foam yields a more sensitive indicator of firmness. For determining serum leakage, a formed square block (defined edge length) of the whipped cream is placed on a special sieve in a room of constant temperature and humidity. After 2 h, the quantity of dripped liquid is measured. Development of the whipped cream structure depends on interactions between fat globules and between fat globules and air bubbles. This leads to the build up of a matrix in which bubbles are stabilized, and the majority of globules are clumped. A prerequisite for effective whipping of the cream is that part of the fat is solid and a spacefilling network of mainly long and slender platelets is formed within the fat globules. Hence, deep cooling and a sufficient cooling time of the cream are indispensable. The initial stage of whipping involves adsorption of soluble whey proteins and -casein at the gas–liquid interface. This protein layer is not strong enough to stabilize a foam structure of large and still rather unstable air cells. However, it makes it easier to incorporate more air into the system until the maximum overrun is achieved. This first stage corresponds more or less to the formation of a protein foam. During the second stage of whipping, the bubbles are reduced in size, and the overrun remains approximately constant. In the end, the proteins are going to be replaced by strongly hydrophobic fat compounds of damaged fat globules. Induced by the mechanical stress, fat globules with slightly protruding fat crystals may collide with an unstable air bubble, and a bridging process occurs. The vigorous flow results also in a more frequent collision of fat globules with protruding crystals which have lost segments of the natural membrane, leading to conjunction of these globules via crystal bridging and released liquid fat as ‘viscous glue’. This partial coalescence results in an irreversible deposition of single fat globules or fat aggregates at the hydrophobic air/serum interface. The highly dynamic transformation of free fat globules into clumps finally leads to the third
stage of whipping. This stage is initiated by a steep increase of power consumption of the whipping device. At the end point, probably only insufficient free fat globules and small clumps remain in the serum phase for the stabilization of newly formed bubble surfaces. The whole process of foam formation results in a partly coalesced fat globule network, which stabilizes the air cells, traps the serum phase, and forms the characteristic stiff texture (Figure 1). This applies to pasteurized or low-pressurehomogenized (max. 3 MPa) UHT whipping cream with a fat content of about 30% and with or without viscosity raising additives. Prolonged whipping would result in too large clumps of fat globules leading to rupture of bubbleenclosing lamella, initiation of bubble coalescence, and a reduction in overrun. The irreversible phase inversion into a greasy water-in-oil emulsion becomes visible as butter granules. Homogenization creates smaller and more stable fat globules which are stabilized by an interface of adsorbed proteins covering an increased total surface area. Such fat globules that are in direct contact with air bubbles do not lose their globule membrane so that no partial coalescence occurs. The secondary membrane exposes the socalled calcium-sensitive regions of the micellar caseins, increasing the reactivity of fat globules. The resulting foam structure is stabilized by casein on the surface of fat globules via calcium bridges. Its development and stability are not comparable with that of nonhomogenized whipped cream (see Cream: Manufacture). Supporting the
Figure 1 Transmission electron micrograph of whipped cream. A, air cell; C, cut fat globule membrane with crystallized fat; F, fat globule; IF, impression of fat globule.
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surface layers with other surface-active substances (emulsifiers) decreases the formation of clusters and increases the tendency to clumping. Then homogenization at higher pressure may be applied. Cream can also be aerated by means of suitable propellants resulting in an overrun of such aerosol products in the range of 300–500%. The resulting microstructure shows a clearly increased amount of fat globules, which adsorb at the interfaces of air bubbles. Concurrently, agglomeration of the fat globules and the corresponding network of different air bubbles is substantially reduced compared with regular whipped cream. The common structure is modified insofar as there is a reduction in the dimensions of the lamellae between air bubbles. The very low level of partial coalescence and the high solubility of the propellants decrease the stability of such foam.
Cultured Cream During the manufacturing process of cultured cream (see Cream: Manufacture), incubation may take place in the retail package or in a fermentation tank. One disadvantage of in-tank souring is that the product will once more come into contact with the manufacturing equipment, which seriously raises the risk of reinfection. Apart from that, the viscosity of the cream after fermentation decreases during mechanical treatment till packaging. Therefore, the necessity of adding hydrocolloids increases. Set-style products have a markedly thicker consistency, but have a tendency to become slightly inhomogeneous during the long fermentation period at ambient temperature. Direct acidified sour cream lacks the fine flavor of cultured cream in the first 2 weeks after production. However, during the following shelf life, enzymes from the culture can start producing an ‘aged’ flavor as a result of proteolysis.
A neck-plug resulting from ordinary creaming only can be mostly redispersed by gentle shaking or even pouring, whereas a more solid kind of plug is not redispersible and thus unacceptable to the consumer. An essential aspect of this neck-plug is its fatty solid-like cohesive structure. So, while creaming remains the prerequisite, considerable variations in storage temperature, especially if accompanied by excessive mechanical agitation, may cause an appreciable destabilization. The formation of a solid neck-plug may be similar in origin to the churning of cream into butter or to the thickening of whipping cream after a short warming up at 30–35 C and subsequent cooling to 5 C (rebodying, see above). Finally, the oil-in-water emulsion is partially converted into a butter-like water-in-oil emulsion. Other physical and chemical factors may also contribute to neck-plugging. At the bottom of the bottle, a slightly granular precipitate is occasionally observed. This deposit is composed of calcium and citrate, and is a direct result of the addition of trisodium citrate. High ambient temperatures during storage of cream liqueur accelerate the production of such crystalline material. The extent of deposition can be reduced by lowering the amount of citrate, but at the same time this increases the probability of subsequent gelation and separation of serum. Hence, it follows that the manufacturer has to assess carefully the composition of and production process for cream liqueurs (see Cream: Manufacture). Finally, it must be taken into consideration that cream liqueur is basically unstable in the presence of lemonade or acidic mixers, because casein coagulates at its isoelectric point (around pH 4.6). The presence of traces of tannins and polyphenolic compounds in added spirits during the manufacture of cream liqueur may also destabilize sodium caseinate emulsions. When using white wine in the formulation of liqueur, the acidity can be neutralized by the addition of sodium hydrogen carbonate.
Cream Liqueur The cream liqueurs that are commercially available have typical shelf lives of several years when stored in sealed bottles under ambient conditions. Very occasionally, however, defects such as the formation of a cream or fat plug in the neck of the bottle can occur after prolonged storage. One explanation is that insufficiently severe homogenization conditions were used (see Cream: Manufacture). There is no analogy between the behavior of double cream in liqueur and pure double cream, for which even slight homogenization results in aggregation of the fat globules. By contrast, it is difficult to overhomogenize a cream liqueur because the fat to protein ratio is about 5, but about 25 in pure double cream.
See also: Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Milk Fat-Based Spreads; The Product and Its Manufacture. Cream: Manufacture. Dehydrated Dairy Products: Milk Powder: Types and Manufacture. Enzymes Indigenous to Milk: Lipases and Esterases. Fermented Milks: Yoghurt: Types and Manufacture. Heat Treatment of Milk: Sterilization of Milk and Other Products; Ultra-High Temperature Treatment (UHT): Aseptic Packaging; Ultra-High Temperature Treatment (UHT): Heating Systems. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Product Types. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk. Packaging. Psychrotrophic Bacteria: Pseudomonas spp.
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Further Reading Anderson M and Brooker BE (1988) Dairy foams. In: Dickinson E and Stainsby G (eds.) Advances in Food Emulsions and Foams, pp. 221–256. London: Elsevier Applied Science. Banks W and Muir DD (1988) Stability of alcohol-containing emulsions. In: Dickinson E and Stainsby G (eds.) Advances in Food Emulsions and Foams, pp. 257–283. London: Elsevier Applied Science. Buchheim W (1986) Ultrastructural aspects and physico-chemical properties of UHT-treated coffee cream. Food Microstructure 5: 181–192. Buchheim W (1991) Mikrostruktur von aufschlagbaren Emulsionen. Kieler Milchwirtschaftliche Forschungsberichte 43: 247–272. Codex Alimentarius Commission (2003) Codex standard for cream and prepared creams. CODEX STAN A-9-1976 Rev. 1-2003. Rome: FAO; WHO. Dickinson E, Narhan SK, and Stainsby G (1989) Stability of alcohol-containing emulsions in relation to neck-plug formation in commercial cream liqueurs. Food Hydrocolloids 3: 85–100. Early R (1998) Liquid milk and cream. In: Early R (ed.) The Technology of Dairy Products, 2nd edn., pp. 1–49. London: Blackie Academic & Professional.
Goff HD (2007) Structure-engineering of ice-cream and foam-based foods. In: McClements DJ (ed.) Understanding and Controlling the Microstructure of Complex Foods. Cambridge: Woodhead. Hoffmann W and Buchheim W (2006) Significance of milk fat in cream products. In: Fox PF and McSweeney PLH (eds.) Advanced Dairy Chemistry, Vol. 2: Lipids, 3rd edn., pp. 365–374. New York: Springer. IDF (1988) Fermented milks: Science and technology. International Dairy Federation Bulletin No. 227. Brussels: IDF. IDF (1992) Monograph on the pasteurization of cream. International Dairy Federation Bulletin No. 271. Brussels: IDF. IDF (1996) UHT cream. International Dairy Federation Bulletin No. 315. Brussels: IDF. Kessler HG (2002) Food and Bio Processing – Dairy Technology., Munich: A. Kessler. pp. 385–424. Smiddy MA, Kelly AL, and Huppertz T (2009) Cream and related products. In: Tamime AY (ed.) Dairy Fats and Related products, pp. 61–85. Chichester, UK: Wiley-Blackwell. Van Aken GA (2001) Aeration of emulsions by whipping. Colloids and Surfaces A: Physicochemical and Engineering Aspects 190: 333–354. Walstra P, Wouters JTM, and Geurts TJ (2006) Dairy Science and Technology, 2nd edn., pp. 447–466. Boca Raton, FL: CRC Press.
Introduction Cream is a comparatively rich emulsion of milk fat. Cream and cream products are sold in many varieties. In most countries, there exist traditional classes of cream products, mostly divided according to the fat content. However, no uniform legal definition and classification has gained worldwide acceptance. The fat content of the different liquid and cultured products ranges from 10 to 50%. Often, subclasses are used. Coffee, half, light, and single cream usually have a fat content of 10–30%, whipping cream has a fat content of 30–40%, and double cream 45–50%. Cream products are also classified according to their thermal treatment. Minimum pasteurization is the best way to preserve cream flavor; however, increasingly, in several countries, more severe heat treatments are practiced for the convenience of extended shelf life at ambient temperatures. Whereas in-bottle sterilization has become less common, ultra-high temperature (UHT) heating and pasteurization with temperatures well above 100 C have gained ground. Nowadays, products such as coffee cream are predominantly flow-sterilized. Cultured or sour creams hold a special position within the range of cream products, because they belong to a diverse group of fermented products. Hence, regulations and manufacturing processes have been adopted from this group. Cream is also used as an essential ingredient in other dairy or nondairy products such as ice cream and cream liqueur (see Cream: Manufacture). In addition, cream is the primary product in the manufacturing process of butter and butter oil (see Butter and Other Milk Fat Products: The Product and Its Manufacture). Some cream products may even be directly used as spreads.
Types and Regulations Cream and cream products have a variety of compositions and are normally defined according to fat content and, sometimes, also by function or heat treatment. Until now, the traditional classes of cream products in different countries have not been made uniform. In 1977, the Food and Agriculture Organization (FAO) and World Health Organization (WHO) suggested
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standards for nonfermented market cream combining fat content and function. Half cream should have a fat content 10 and <18%, cream 18%, whipping cream 28%, heavy whipping cream 35%, even though higher fat creams are less dense and thus lighter per unit volume, and double cream 45%. However, these suggestions did not prevail over national legislation. A new initiative was taken by the Codex Alimentarius Milk Commission and the International Dairy Federation (IDF). The revised ‘Codex Standard for Cream and Cream Products’ (2003) describes cream as ‘‘. . . the fluid milk product comparatively rich in fat, in the form of an emulsion of fat-in-skimmed milk, obtained by physical separation from milk. Prepared creams are the milk products obtained by subjecting cream . . . to suitable treatments and processes to obtain the characteristic properties as specified below.’’ These prepared creams comprise prepackaged liquid cream, whipping and whipped cream, cream packed under pressure (aerosol whipping cream), fermented cream, and acidified cream. The minimum fat content of all these creams has to be 10%. National regulations make more distinctions regarding fat content. Products with a low fat content are German ‘coffee cream’ (10% fat), ‘half-and-half cream’ (10.5% fat) in the United States, and British ‘half cream’ (12% fat). Traditional (whipping) cream contains 30% fat in Germany and the Netherlands, whereas the same product contains 35% fat in the United Kingdom, Australia, and New Zealand. The US Food and Drug Administration makes a distinction between ‘light whipping cream’ (30% fat) and ‘heavy whipping cream’ (36% fat). Applied heat treatments for the different cream products include pasteurization, UHT heating (135 C), flow sterilization in a UHT plant (<135 C), and in-bottle sterilization (see Heat Treatment of Milk: Sterilization of Milk and Other Products; Ultra-High Temperature Treatment (UHT): Aseptic Packaging. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk). Cultured or sour creams are regulated as are fermented products. Their fat content also ranges from 10 to more than 40%. In the United Kingdom and the United States, a minimum fat content of 18% is required. In countries such as France, Germany, Denmark, and Sweden, the term ‘cre`me fraıˆche’ has a different definition in each nation’s legislation. ‘Smetana’ is a popular sour cream product in eastern Europe and Finland. In the
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United States, the addition of ‘acidified’ to the name means that the cream is soured with safe and suitable acidifiers such as gluconic acid--lactone, with or without the addition of lactic acid bacteria. The manufacturing processes of cultured creams are largely similar to those of other fermented products (see Fermented Milks: Yoghurt: Types and Manufacture). ‘Clotted cream’ (55% fat) is a product that is virtually unique to South West England and is used for tea and dessert (with scones and jam). A thin layer of cream is heated at about 80 C for 1 h (scalding), resulting in a cream crust and a rich, sweet flavor. Similar products are ‘o¨rom’ (Mongolia), ‘malai’ (India), and ‘kaymak’ (Near and Middle East). Cream liqueurs, which contain an essential amount of cream, are normally regulated as are spirits. In a cream liqueur produced in the European Union, 15% of cream with 10% fat is required. Removal of water from cream by spray-drying yields cream powders with an extended shelf life if antioxidants are added and adequate storage conditions are guaranteed. To obtain functional products after reconstitution, incorporation of emulsifiers, such as monoacylglycerols, is necessary. Legally, cream powders normally belong to the group of dry milk products (see Dehydrated Dairy Products: Milk Powder: Types and Manufacture). There are many more products with the word ‘cream’ in their designation. Well-known examples are ice cream, cream cheeses, and cream spreads (see Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Milk Fat-Based Spreads. Cream: Manufacture. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Product Types). During the manufacturing process of liquid cream products, certain substances can be added if legally permitted. Typically, coffee cream contains stabilizing salts such as phosphates and citrates, and the creaming of whipping cream within the package is delayed by carrageenan, which also reduces syneresis after whipping. Cream liqueurs are stabilized by citrate, whereas cultured cream products are usually processed without adding hydrocolloids. In the European Union, the legal regulations concerning additives have been uniform for some years. The permitted substances in liquid cream comprise phosphoric acid and mono-, di-, tri-, and polyphosphates, lactic acid and lactates, citric acid and citrates, chlorides, alginic acid and alginates, agar-agar, carrageenan, xanthan gum, pectins, cellulose and cellulose derivates, starch derivates, emulsifiers (lecithin and mono- and diacylglycerols of edible fatty acids), and the propellants carbon dioxide, nitrogen, or dinitrogen monoxide in whipped creams. Not all of the additives on this extensive list are, however, really helpful or necessary for the production of high-quality cream products, and hence not all are used.
Quality Problems Coffee Cream In many countries, coffee cream is a popular product, which is manufactured for long storage either by in-bottle sterilization or by flow sterilization in a UHT plant. It competes with evaporated milk, liquid or foamed whole milk, and liquid or dried coffee whiteners, which often contain vegetable fats. After opening of a briefly shaken cream package, the consumer expects good sensory properties of the content and that the ingredients, that is, fat and protein, have remained in a homogeneously dispersed state. In a hot coffee beverage, a high whitening effect as well as a high coffee stability is demanded. Coffee stability, which is of outstanding importance for the quality of this product, means the degree of resistance against coagulation or ‘feathering’. Creaming or sedimentation phenomena during storage depend on the fat content of cream and on the conditions of heat treatment and homogenization during the manufacturing process (see Cream: Manufacture). It is obvious that creaming problems increase with the fat content. The fat content is limited to about 20% to obtain a desirable homogenization effect (volume-moment average diameter 0.4–0.6 mm, nearly identical size) because casein is partly bound to the fat as a major constituent of the newly formed fat globule membrane. The considerable enlargement of the total fat globule surface after homogenization as a result of the increased globule numbers and its reduced diameter requires a sufficient amount of casein, that is, a sufficiently high protein/fat ratio. The more the available casein is adsorbed on the fat globules, the more the aggregation of fat/protein complexes is favored (due to the higher sensitivity to changes in electrical charge). A thermally induced aggregation may occur during in–bottle or flow sterilization of the coffee cream. Its extent depends more on the heating temperature than on the heating time. That is why flow sterilization is carried out preferably with temperatures below 130 C. In addition, the process of flow sterilization in a UHT plant allows a second two-stage homogenization after heating in order to split up aggregates (clusters) formed. A resulting coffee cream with predominantly nonaggregated fat globules shows a low viscosity, which is a desirable characteristic. The aggregation of fat/protein complexes in hot coffee solutions is affected by the manufacturing process of the cream, but also by coffee brand, water ingredients, brewing conditions, actual temperature, and other factors. Most coffee solutions have pH values of about 5.0, which is near the isoelectric point of casein. In combination with high temperatures and low or very high water hardness, coagulation and aggregation can easily occur. When the temperature of a cold coffee solution with dispersed cream increases, the growing aggregates remain
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invisible to the naked eye until they have a sufficient size. At this temperature, feathering becomes perceptible and the whitening power of the cream decreases at the same time. After pouring the coffee cream from a small polystyrene (PS) package into a coffee solution, clearly defined large white floccules can float on the surface, and this is not a result of feathering. These floccules are dried particles from inside the package that were formed during storage because PS permits substantial water vapor permeability (see Packaging).
Whipping Cream The whipping of a traditionally pasteurized, continuously and sufficiently cooled cream with a fat content of not less than 30% is unproblematic if a raw milk of good quality is used and the production of cream continues largely without mechanical stress. Each additional percent of fat up to 40% reduces whipping time and results in a firmer foam. Quality defects of raw milk, nonoptimal processing, a lower fat content, and, most of all, the demand for a prolongation of shelf life generally cause problems. Raw milk contains enzymes with different activities and some of them are responsible for the development of specific flavor compounds and defects in milk and cream. The native milk lipase, for example, is lipoprotein lipase (LPL) that catalyzes the hydrolysis of triacylglycerols to free fatty acids. The activity of LPL is theoretically sufficient to cause rancidity in less than 1 min. However, liberation of free fatty acids is prevented by an intact milk fat globule membrane. Since the fat globule membrane protects milk fat against lipolysis, the milk must be carefully handled to minimize damage to the fat globule membrane. Homogenization of cream produces a greatly enlarged area of milk fat covered with a new membrane. This milk fat is vulnerable to the action of LPL, and subsequent rancidity occurs if no immediate pasteurization inactivates this heat-labile enzyme. Lipolytic rancidity is also induced by extracellular bacterial lipases of Pseudomonas spp. and other Gram-negative psychrotrophs. In many cases, these lipases are not inactivated by pasteurization and may even be present in UHT cream (e.g., lipases of Pseudomonas fluorescens). Extracellular proteinases of Gram-negative psychrotrophs may be also very heat-stable and can show activity even after in-bottle sterilization of cream. Phospholipases, proteinases, and glycosidasas from psychrotrophic Pseudomonas, Citrobacter, and Enterobacter may act synergistically in damaging the fat globule membrane. The aggregation of fat globules, which produces bitty cream, has been linked to the specific activity of phospholipase from Bacillus cereus. Psychrotrophic spore formers in raw milk such as Bacillus spp., which cause sweet coagulation, can survive pasteurization, and also
heat-resistant spores may occur in UHT cream (see Enzymes Indigenous to Milk: Lipases and Esterases. Psychrotrophic Bacteria: Pseudomonas spp.). The prolonged shelf life of UHT cream means that high demands are made on filling and packaging materials. In contrast to pasteurized cream, the UHT product must be aseptically filled and packed. Therefore, the filling equipment and packaging materials have to be tolerant to water, steam, hydrogen peroxide, heat, and UV light. Whether the whipping cream is pasteurized or UHT heated, there are some common important factors that must be taken into consideration. Light and/or oxygen may induce oxidation of unsaturated fatty acids, leading to flavor degradation. The appropriate filling conditions should be selected to minimize the oxygen content in the package (with small headspace volume) and in the cream (see Packaging). Homogenized cream is particularly susceptible to the action of light. The sensitivity of cream to light depends also on the heating conditions. UHT heating causes sulfhydryl groups and hydrogen sulfide to be released from -lactoglobulin, initially creating an intense cooked flavor (see Heat Treatment of Milk: Ultra-High Temperature Treatment (UHT): Aseptic Packaging; Ultra-High Temperature Treatment (UHT): Heating Systems). During storage, oxidation of these groups causes the cooked flavor to disappear and the strong reducing activity inhibits the development of off-flavor compared with those likely to occur in pasteurized cream. A balanced antioxidative/oxidative action of sulfhydryl groups and oxygen will probably help to ensure cream products of a good sensory quality. But even if well-balanced conditions can be maintained, light transmission must be kept at a low level. UHT whipping cream is expected to have a shelf life of about 3 months. But particularly during the summer period, consumers complain about quality defects. A short-lived warming up of a cream package to a temperature of 30–35 C, as may occur during transport without cooling, produces adverse effects after slow recooling. It not only supports creaming during subsequent storage at 20 C, but may also lead to a distinct thickening after cooling before whipping. Although not all the fat is melted after the warming up, this ‘rebodying’ is caused by increased size of fat crystals during recooling. This results in partial coalescence without stirring provided that the fat content is so high that the fat globules are very close together. A continuous storage temperature of 5 C delays creaming and the occurrence of sensory problems when compared to storage at 20 C. The whipping time of the cream is extended as a result of cold storage, but it also results in an increased volume. Whenever comparative studies or assessments of whipping properties are carried out, standardized temperature and whipping conditions must be ensured, for
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which special regulations exist in many countries. Usually, whipping time and overrun, and firmness and leakage of the foam are measured. Most devices used to test whipping are modifications of the one originally described by Mohr and Baur in 1937. It consists of two hexagonal, cylindrically arranged wire baskets rotating at a constant speed. The cream, which is stored for 24 h at 4 C, is whipped in standardized cooled (5 C) cups until there is no appreciable increase in the load required to turn the blades. Percent overrun is calculated as the volume difference after and before whipping, divided by the volume of unwhipped cream and multiplied by 100. An overrun of not less than 80% is desirable. Firmness can be equated with the length of time needed by a standardized plunger to penetrate the foam to a defined depth. When using a texture analyzer, the average force required to move the plunger at a constant speed within the foam yields a more sensitive indicator of firmness. For determining serum leakage, a formed square block (defined edge length) of the whipped cream is placed on a special sieve in a room of constant temperature and humidity. After 2 h, the quantity of dripped liquid is measured. Development of the whipped cream structure depends on interactions between fat globules and between fat globules and air bubbles. This leads to the build up of a matrix in which bubbles are stabilized, and the majority of globules are clumped. A prerequisite for effective whipping of the cream is that part of the fat is solid and a spacefilling network of mainly long and slender platelets is formed within the fat globules. Hence, deep cooling and a sufficient cooling time of the cream are indispensable. The initial stage of whipping involves adsorption of soluble whey proteins and -casein at the gas–liquid interface. This protein layer is not strong enough to stabilize a foam structure of large and still rather unstable air cells. However, it makes it easier to incorporate more air into the system until the maximum overrun is achieved. This first stage corresponds more or less to the formation of a protein foam. During the second stage of whipping, the bubbles are reduced in size, and the overrun remains approximately constant. In the end, the proteins are going to be replaced by strongly hydrophobic fat compounds of damaged fat globules. Induced by the mechanical stress, fat globules with slightly protruding fat crystals may collide with an unstable air bubble, and a bridging process occurs. The vigorous flow results also in a more frequent collision of fat globules with protruding crystals which have lost segments of the natural membrane, leading to conjunction of these globules via crystal bridging and released liquid fat as ‘viscous glue’. This partial coalescence results in an irreversible deposition of single fat globules or fat aggregates at the hydrophobic air/serum interface. The highly dynamic transformation of free fat globules into clumps finally leads to the third
stage of whipping. This stage is initiated by a steep increase of power consumption of the whipping device. At the end point, probably only insufficient free fat globules and small clumps remain in the serum phase for the stabilization of newly formed bubble surfaces. The whole process of foam formation results in a partly coalesced fat globule network, which stabilizes the air cells, traps the serum phase, and forms the characteristic stiff texture (Figure 1). This applies to pasteurized or low-pressurehomogenized (max. 3 MPa) UHT whipping cream with a fat content of about 30% and with or without viscosity raising additives. Prolonged whipping would result in too large clumps of fat globules leading to rupture of bubbleenclosing lamella, initiation of bubble coalescence, and a reduction in overrun. The irreversible phase inversion into a greasy water-in-oil emulsion becomes visible as butter granules. Homogenization creates smaller and more stable fat globules which are stabilized by an interface of adsorbed proteins covering an increased total surface area. Such fat globules that are in direct contact with air bubbles do not lose their globule membrane so that no partial coalescence occurs. The secondary membrane exposes the socalled calcium-sensitive regions of the micellar caseins, increasing the reactivity of fat globules. The resulting foam structure is stabilized by casein on the surface of fat globules via calcium bridges. Its development and stability are not comparable with that of nonhomogenized whipped cream (see Cream: Manufacture). Supporting the
Figure 1 Transmission electron micrograph of whipped cream. A, air cell; C, cut fat globule membrane with crystallized fat; F, fat globule; IF, impression of fat globule.
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surface layers with other surface-active substances (emulsifiers) decreases the formation of clusters and increases the tendency to clumping. Then homogenization at higher pressure may be applied. Cream can also be aerated by means of suitable propellants resulting in an overrun of such aerosol products in the range of 300–500%. The resulting microstructure shows a clearly increased amount of fat globules, which adsorb at the interfaces of air bubbles. Concurrently, agglomeration of the fat globules and the corresponding network of different air bubbles is substantially reduced compared with regular whipped cream. The common structure is modified insofar as there is a reduction in the dimensions of the lamellae between air bubbles. The very low level of partial coalescence and the high solubility of the propellants decrease the stability of such foam.
Cultured Cream During the manufacturing process of cultured cream (see Cream: Manufacture), incubation may take place in the retail package or in a fermentation tank. One disadvantage of in-tank souring is that the product will once more come into contact with the manufacturing equipment, which seriously raises the risk of reinfection. Apart from that, the viscosity of the cream after fermentation decreases during mechanical treatment till packaging. Therefore, the necessity of adding hydrocolloids increases. Set-style products have a markedly thicker consistency, but have a tendency to become slightly inhomogeneous during the long fermentation period at ambient temperature. Direct acidified sour cream lacks the fine flavor of cultured cream in the first 2 weeks after production. However, during the following shelf life, enzymes from the culture can start producing an ‘aged’ flavor as a result of proteolysis.
A neck-plug resulting from ordinary creaming only can be mostly redispersed by gentle shaking or even pouring, whereas a more solid kind of plug is not redispersible and thus unacceptable to the consumer. An essential aspect of this neck-plug is its fatty solid-like cohesive structure. So, while creaming remains the prerequisite, considerable variations in storage temperature, especially if accompanied by excessive mechanical agitation, may cause an appreciable destabilization. The formation of a solid neck-plug may be similar in origin to the churning of cream into butter or to the thickening of whipping cream after a short warming up at 30–35 C and subsequent cooling to 5 C (rebodying, see above). Finally, the oil-in-water emulsion is partially converted into a butter-like water-in-oil emulsion. Other physical and chemical factors may also contribute to neck-plugging. At the bottom of the bottle, a slightly granular precipitate is occasionally observed. This deposit is composed of calcium and citrate, and is a direct result of the addition of trisodium citrate. High ambient temperatures during storage of cream liqueur accelerate the production of such crystalline material. The extent of deposition can be reduced by lowering the amount of citrate, but at the same time this increases the probability of subsequent gelation and separation of serum. Hence, it follows that the manufacturer has to assess carefully the composition of and production process for cream liqueurs (see Cream: Manufacture). Finally, it must be taken into consideration that cream liqueur is basically unstable in the presence of lemonade or acidic mixers, because casein coagulates at its isoelectric point (around pH 4.6). The presence of traces of tannins and polyphenolic compounds in added spirits during the manufacture of cream liqueur may also destabilize sodium caseinate emulsions. When using white wine in the formulation of liqueur, the acidity can be neutralized by the addition of sodium hydrogen carbonate.
Cream Liqueur The cream liqueurs that are commercially available have typical shelf lives of several years when stored in sealed bottles under ambient conditions. Very occasionally, however, defects such as the formation of a cream or fat plug in the neck of the bottle can occur after prolonged storage. One explanation is that insufficiently severe homogenization conditions were used (see Cream: Manufacture). There is no analogy between the behavior of double cream in liqueur and pure double cream, for which even slight homogenization results in aggregation of the fat globules. By contrast, it is difficult to overhomogenize a cream liqueur because the fat to protein ratio is about 5, but about 25 in pure double cream.
See also: Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Milk Fat-Based Spreads; The Product and Its Manufacture. Cream: Manufacture. Dehydrated Dairy Products: Milk Powder: Types and Manufacture. Enzymes Indigenous to Milk: Lipases and Esterases. Fermented Milks: Yoghurt: Types and Manufacture. Heat Treatment of Milk: Sterilization of Milk and Other Products; Ultra-High Temperature Treatment (UHT): Aseptic Packaging; Ultra-High Temperature Treatment (UHT): Heating Systems. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Product Types. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk. Packaging. Psychrotrophic Bacteria: Pseudomonas spp.
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Further Reading Anderson M and Brooker BE (1988) Dairy foams. In: Dickinson E and Stainsby G (eds.) Advances in Food Emulsions and Foams, pp. 221–256. London: Elsevier Applied Science. Banks W and Muir DD (1988) Stability of alcohol-containing emulsions. In: Dickinson E and Stainsby G (eds.) Advances in Food Emulsions and Foams, pp. 257–283. London: Elsevier Applied Science. Buchheim W (1986) Ultrastructural aspects and physico-chemical properties of UHT-treated coffee cream. Food Microstructure 5: 181–192. Buchheim W (1991) Mikrostruktur von aufschlagbaren Emulsionen. Kieler Milchwirtschaftliche Forschungsberichte 43: 247–272. Codex Alimentarius Commission (2003) Codex standard for cream and prepared creams. CODEX STAN A-9-1976 Rev. 1-2003. Rome: FAO; WHO. Dickinson E, Narhan SK, and Stainsby G (1989) Stability of alcohol-containing emulsions in relation to neck-plug formation in commercial cream liqueurs. Food Hydrocolloids 3: 85–100. Early R (1998) Liquid milk and cream. In: Early R (ed.) The Technology of Dairy Products, 2nd edn., pp. 1–49. London: Blackie Academic & Professional.
Goff HD (2007) Structure-engineering of ice-cream and foam-based foods. In: McClements DJ (ed.) Understanding and Controlling the Microstructure of Complex Foods. Cambridge: Woodhead. Hoffmann W and Buchheim W (2006) Significance of milk fat in cream products. In: Fox PF and McSweeney PLH (eds.) Advanced Dairy Chemistry, Vol. 2: Lipids, 3rd edn., pp. 365–374. New York: Springer. IDF (1988) Fermented milks: Science and technology. International Dairy Federation Bulletin No. 227. Brussels: IDF. IDF (1992) Monograph on the pasteurization of cream. International Dairy Federation Bulletin No. 271. Brussels: IDF. IDF (1996) UHT cream. International Dairy Federation Bulletin No. 315. Brussels: IDF. Kessler HG (2002) Food and Bio Processing – Dairy Technology., Munich: A. Kessler. pp. 385–424. Smiddy MA, Kelly AL, and Huppertz T (2009) Cream and related products. In: Tamime AY (ed.) Dairy Fats and Related products, pp. 61–85. Chichester, UK: Wiley-Blackwell. Van Aken GA (2001) Aeration of emulsions by whipping. Colloids and Surfaces A: Physicochemical and Engineering Aspects 190: 333–354. Walstra P, Wouters JTM, and Geurts TJ (2006) Dairy Science and Technology, 2nd edn., pp. 447–466. Boca Raton, FL: CRC Press.