Ice Cream Technology
- 2. What is Ice Cream? • Ice cream is a sweetened frozen food typically eaten as a snack or dessert. It is usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavors. It is typically sweetened with sugar or sugar substitutes. Typically, flavourings and colourings are added in addition to stabilizers. • The mixture is stirred to incorporate air spaces and cooled below the freezing point of water to prevent detectable ice crystals from forming. The result is a smooth, semi-solid foam that is solid at very low temperatures.
- 3. Top Ice Creams producers in world (2016) General Mills 15% Meiji Holding 3% Mihan Dairy Group 4% Nestle 16% Unilever 57% Well's Dairy 5%
- 4. Top Ice Creams brands in 2016
- 5. Approximate Composition (percentage by weight) of some types of ice cream Constituent Dairy Ice Cream Ice Milk Sherbet Ice Lolly Milk fat 10 4 2 0 Nonfat milk solids 11 12 4 0 Added sugar 14 13 22 22 Additives 0,4 0,6 0,4 0,2 % Overrun 100 85 50 ~0 Edible energy, kJ/100 ml 390 300 340 370
- 6. Flow chart of Ice Creams production
- 7. Ice cream composing • Composing the mix is relatively simple. The additives are „emulsifier”, stabilizer (a thickening agent, usually a mixture of polysaccharides), and flavor and color substances. • Clearly, ingredients such as fruit pulp and ground nuts should be added after the homogenization
- 8. Pasteurization • Pasteurization of the mix primarily serves to kill pathogenic and spoilage microorganisms. Additives added after homogenization should usually be pasteurized separately. The second important objective is to inactivate lipase because it is still a little active even at a very low temperature. Bacterial lipases should thus be prevented from occurring. • Finally, quite intense heating of the mix is desirable (especially for hardened ice cream) to decrease its susceptibility to autoxidation; a cooked flavor may be undesirable, according to the added flavor substances.
- 9. Homogenization • Homogenization is specifically meant to give the ice cream a sufficiently fine, smooth texture. Excessive formation of homogenization clusters should be avoided as it causes the mix to become highly viscous and the desirable fine texture not to be achieved; consequently, the homogenization pressure should be adapted to the fat content, to the pasteurization intensity, and, if need be, to the further composition of the mix.
- 10. Cooling and ripening • Cooling and ripening (keeping cold for some time) are desirable for two reasons. The fat in most of the fat globules should largely be crystallized before the ice cream mix enters the freezer; it is important to note that considerable undercooling may occur because the fat globules are very small. • Certain stabilizers such as gelatin and locust bean gum need considerable time to swell after being dispersed. Some added emulsifiers need considerable time at low temperature to displace protein from the fat globules.
- 11. Freezing • Freezing implies rapid cooling of the mix to a few degrees below zero; in this way, ice is formed while air is beaten in. This must run simultaneously: after the bulk of the water is frozen, any beating in of air becomes impossible, and freezing after air is beaten in leads to insufficient churning of the fat globules and can damage the foam structure. • Moreover, the vigorous beating enables rapid cooling, because of which small ice crystals can be formed.
- 12. Freezing • Usually, freezing is done in a scraped-surface heat exchanger — essentially a horizontal cylinder that is cooled externally by means of direct evaporation (−20 to −30°C) and equipped with a rotating stirrer (150 to 200 r.p.m.) that scrapes the wall. A layer of ice is formed on the wall. Pieces of ice are broken from the layer by the scraper and are distributed throughout the mass. • The process of manufacture takes a few minutes. The mix leaves the freezer at −3.5 to −7°C. A second heat exchanger may be applied, in which the mix is cooled further, while stirred, to about −10°C without additional beating in of air. Deeper cooling cannot be achieved in a flow-type exchanger because the product becomes too firm.
- 13. Packaging • Packaging of ice cream often is a complicated operation, especially if mixtures or exceptional shapes are wanted. In the latter case the packaging step may be associated with the start of the hardening in order to give the portions appropriate shape retention.
- 14. Hardening • The hardening process serves to rapidly adjust the temperature of the ice cream to such a level as to retain its shape and to give it a sufficient shelf life with respect to chemical and enzymatic reactions, as well as to the physical structure. • The packaged ice cream can be passed through a so-called hardening tunnel, in which very cold air (say, −40°C) is blown past the small packages for some 20 min. Likewise, packaged ice cream can be passed through a brine bath of low temperature.
- 15. Role of the various components Fats Milk solids-not-fat Sugar Stabilizer Emulsifier
- 16. Fats • Fat is of special importance for the flavor and for a solid structure to be formed during freezing and therefore for consistency, appearance, and melting resistance. • A high fat content leads to a dry, almost grainy texture, a low fat content to a smooth, homogeneous, somewhat slimy texture.
- 17. Milk solids-not-fat • Milk solids-not-fat contribute to the flavor. They are also responsible for part of the freezing- point depression and for an increased viscosity. The protein partly serves to stabilize the foam lamellae during air incorporation; it is essential for the formation of fat-globule membranes during homogenization. • Lactose can crystallize at low temperature. The crystals formed should be small in order to prevent sandiness. To that end, cooling should be quick during freezing, and afterward temperature fluctuations should be avoided.
- 18. Sugar • Sugar, often sucrose, is essential for the taste and for the freezing-point depression. Too little sugar may cause too much ice to be formed; too much sugar often makes the ice cream overly sweet. To overcome this, part of the sucrose may be replaced by a substitute such as glucose syrup, which is less sweet and leads to a greater freezing-point depression per kg sugar. • The sugar also causes a higher viscosity, especially when most of the water has been frozen. However, the most important role of the sugar is that it causes far less water to freeze than otherwise would be the case. As a result, the consistency of the ice cream is softer and its mouthfeel less cold.
- 19. Stabilizer • The role of the stabilizer or, more properly speaking, of the thickening agent is not quite clear. Among those used are gelatin, alginate, carrageenan, pectin, locust bean gum, guar gum, xanthan, carboxymethyl cellulose, and mixtures. Of course, these substances affect the consistency and, consequently, also the heat transfer during the freezing. If little clumping of fat globules occurs as, for instance, in low-fat ices, the desired firmness and prevention of excessive Ostwald ripening of air bubbles must be achieved by means of thickening agents. • However, these agents may cause the consistency of the product to become somewhat slimy in the mouth. Furthermore, the thickening agents are often assumed to counteract the Ostwald ripening of ice and lactose crystals, and even to prevent crystallization of lactose. Many thickening agents at high concentrations (as is the case in ice cream at low temperature) do, indeed, lower the crystallization rate and thereby slow down Ostwald ripening, but it is very unlikely that they can inhibit crystallization.
- 20. Emulsifier • Emulsifier is not needed in the proper sense of the word (more than sufficient protein is present during homogenization) and it does not play a significant role in foam formation either. • It serves to stimulate the fat globules to clump and to become attached to the air bubbles. The emulsifiers used include egg yolk, monoglycerides, poly(oxyethylene) sorbitan esters (Tweens), and esters from citric acid and monoglycerides.