The Production of Ice-cream

The flavouring can be added before, during or after the ageing. The flavouring is added either directly to the mix after the pasteurisation or together with the fruit or food preparation. The preparation should be sterile or pasteurized. 

Generally, the flavour should be added at the lowest possible temperature in the process to prevent evaporative losses of volatile flavour nuances [9]. 

The procedure of ageing and freezing is a very important process. During the ageing process the macro-molecules need time for their hydration. This time has to be balanced between economy, hydration of the stabilizers, flavour building and the danger of microbiological infection. 

The freezing process influences the building of the phases of ice, air and fat. The maximum size of ice crystals may not exceed 60 pm, otherwise the crystals could be detected by the consumer. 

In the beginning only a limited range of unflavoured dairy products was on the market. Then, after manufactures started adding (fruit) preparations or flavourings, there was a significant increase in the number and type of dairy products on the market. 

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Bubbles are critical in manufacturing in the food industry. The stability and size of the bubbles determines the taste and the looks of the product. In industry, much research has been done on the factors that control bubble formation and stability. This is of special interest in the production of ice cream, where air bubbles are trapped in frozen material. 

By pre-treating milk with lactase, all adults can enjoy milk and a whole range of other lactose-free dairy products can be made such as ice cream and yogurt. In the production of ice cream, lactose hydrolysis can also be used to improve certain properties such as the texture, sweetness and tendency to crystallize. The increased sweetness is also advantageous in the manufacture of flavored milk products because less sugar needs to be added. 

Glucose-galactose syrups are about three times sweeter than lactose (70% as sweet as sucrose) and hence lactose-hydrolysed milk could be used in the production of ice-cream, yoghurt or other sweetened dairy products, permitting the use of less sucrose and reducing caloric content. However, such applications have not been commercially successful. 

Probiotics have been included successfully in ice cream. Relevant to this book is the production of ice cream based on frozen yogurt, which basically follows the same manufacturing as probiotic yogurt (Davidson, Duncan, Hackney, Eigel, Boling, 2000). But probiotics can also be included in the ice cream base or in a chocolate coating of the ice cream. 

Dextran is used mostly in medicine as a blood substitute. In the food industry it is used as a thickening and stabilizing agent, as exemplified by its use in baking products, confections, beverages and in the production of ice creams. 

For the production of ice cream, the mixture of components is subjected to high-temperature short-time pasteurization (80-85 °C, 20-30 s), high-pressure homogenization (150-200 bar) and cooling to ca. 5 °C. Air is then mixed into the mixture (60-100 vol%) while it is frozen at temperatures of up to —10 °C and then hardened. The freezers used are mainly continuously working systems furnished with coolants which evaporate at —30 °C to —40 °C. The process is controlled in such a way that the core temperature of the ice cream production is ca. —18 °C. 

Ice-cream must be kept at low temperature right up to the point of final consumption. If it is allowed to soften, the entrained air bubbles may escape and the original texture will be lost. If it softens and is then re-frozen, a hard, solid skin forms, making the product inedible. Ice-cream must always be handled quickly when passing through transit stages from the factory to consumer. 

A typical characteristic of many food products is that these are multi-phase products. The arrangement of the different phases leads to a microstructure that determines the properties of the product. Mayonnaise, for example, is an emulsion of about 80% oil in water, stabilized by egg yolk protein. The size of the oil droplets determines the rheology of the mayonnaise, and hence, the mouthfeel and the consumer liking. Ice cream is a product that consists of four phases. Figure 1 shows this structure schematically. Air bubbles are dispersed in a water matrix containing sugar molecules and ice crystals. The air bubbles are stabilized by partial coalesced fat droplets. The mouthfeel of ice cream is determined by a combination of the air bubble size, the fat droplet size and the ice crystal size. 

Food Product and Agricultural Applications Table 13.2 Illustration of the composition of ice cream. 

Sugar hydrolysis increases the number of solutes in the food matrix, resulting in a reduction in the amount of ice in the product, which may alter certain physical properties for example, the hrmness of ice cream was found to inversely relate to the degree of hydrolysis (Lim et al., 2004). 

Glass transition temperatures are most often determined by DSC and by thermomechanical analysis (TMA) (Goff, 1994). Table 7.5 shows the T of some food products. Tg is strongly affected by the composition of the matrix also depends on the procedure used to determine its value. In the case of ice creams, for example, depends on the recipe, particularly on the level of sugars. As Brake and Fennema... 

The term ice cream is so indefinite and includes so many different products that the bacteriology of ice cream is also very indefinite. Some manufacturers take advantage of this fact at present as an excuse for an unsanitary product. 

In the food production industry, where it is used in the removal of peels from fruits and vegetables, the carme-lization of products that contain sugar, the thickening of ice cream, the softening of olives, the production of chocolate and cocoa, and the preparation of hominy from corn kernels ... 

To describe the science of ice cream, it is first necessary to describe some of the physical chemistry and colloid science that underpins it these are laid out in Chapter 2. Chapters 3 and 4 cover the ingredients and the ice cream making process respectively. Chapter 5 focuses on the production of various types of ice cream product. The physical and sensory measurements used to quantify and describe it are discussed in Chapter 6, and the micro structure, and its relationship to the texture, is examined in Chapter 7. Finally, Chapter 8 describes a number of... 

Ice cream is made and eaten in almost every country in the world. The total worldwide production of ice cream and related frozen desserts was 14.4 billion litres (1) in 2001, i.e. an average of 2.4 litres per person, worth 35 billion." Unilever and Nestle are the largest worldwide producers, with about 17 and 12% of the market respectively. A huge range of different flavours is available, including savoury ones. Differences in culture and climate produce wide variations in the amounts, types and flavours of ice cream produced and consumed in different countries. 

Two factors that have a major effect on the sales of ice cream products are the weather and advertising. Ice cream sales in the UK are very seasonal, peaking in the summer. In France, 65% of sales are made between June and September, and in Italy the average consumption... 

The ingredients of ice cream products can be classified in three groups ... 

The Science of Ice Cream begins with an introductory chapter on the history of ice cream. Subsequent chapters outline the physical chemistry underlying its manufacture, describe the ingredients and industrial production of ice cream and ice cream products respectively, detail the wide range of different physical and sensory techniques used to measure and assess ice cream, describe its microstructure (i.e. ice crystals, air bubbles, fat droplets and sugar solution), and how this relates to the physical properties and ultimately the texture that you experience when you eat it. Finally, some suggestions are provided for experiments relating to ice cream and ways to make ice cream at home or in a school laboratory. 

Products that can be readily substituted for each other are said to have high cross price elasticity of demand. This point applies not only to brands within one product class but also to different product classes. For example, as the price of ice cream goes up, consumers may switch to cakes for dessert, thereby increasing the sales of cake mixes. 

Because of the importance of ice cream as a product, much has been written on its stmcture and for mation (171), and the process can only be summarized here. In toppings and ice cream (and indeed simply in whipping cream), it is first necessary to produce a stable emulsion. Ice-cream mix is a complex mixtiue, but the initial emulsion is basically homogenized milk, containing an admixture of small-molecule siufactants as well in whipped toppings, the emulsion is made with oil and a surfactant mixture, which may or may not contain protein and in cream, the natural membrane of phospholipid and protein surrounds the milk fat. In all of these, it is necessary to have some small-molecule emulsifiers so as to exchange with, and weaken the rigidity of, the adsorbed layer of protein (118). The second essential is fliat the fat or oil in the formulation is partly crystalline neiflier completely liquid nor completely solid oil will perform optimally. If the oil is partly crystalline, then the emulsion droplets may not be truly spherical but may have protrusions of crystals on their surfaces. 

Starch phosphates are useful in frozen foods where they impart good freeze-thaw stability and reduce retrogradation (Chapter 10.1). The stability of ice cream and other products can also be improved. Starch phosphates can be used as cheese emulsifiers [67] and phosphates incorporated into flour will improve its properties by reaction with the starch [68]. Calcium starch phosphates are claimed to be useful components of foods, animal feeds and pharmaceutical products [69]. 

A stabilization problem with conventional ice cream is that at deep-freeze temperatures they cannot be served or eaten as readily as when they are at normal eating temperature. Reformulation to ensure such properties, e.g., spoonability at deepfreeze temperatures, as approximately those expected at normal eating tanperatures is comparatively simple. The difficulty is that such reformulation leads to products that do not have acceptable properties at normal eating temperatures. The properties of ice creams, that have the serving and eating properties conventionally expected at normal eating temperatures and that are sufficiently stable, are improved by... 

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