Ice Cream in the Factory

When ice cream leaves the factory freezer at about — 5 °C, its ice content is only about half that at a typical serving temperature of —18 °C, so it is very soft. As shown in Chapter 2, the microstructure of dispersed ice crystals and air bubbles is thermodynamically unstable -the system tends towards a state in which the phases are less dispersed. If the ice cream were simply stored at the factory freezer outlet temperature it would deteriorate very quickly. The ice crystals and air bubbles would coarsen their mean size would increase and their total number would decrease. Since it is not possible to stabilize the microstructure thermodynamically, the best that can be achieved is to trap it kinetically, i.e. to slow down the rate at which coarsening occurs, so that significant... 

Hardening The second freezing step in the manufacturing process in which partly frozen ice cream from the factory freezer is placed in a... 

Milk is converted in the creamery and associated factories to whole or market milk, skimmed milk, creams, hutters, cheeses, dried milk, whey, yoghurts, hutter oil, condensed milk, milk powder and ice cream [46]. 

No trip to Vermont is complete without a visit to Ben Jerry s famous ice cream factory. If there are happier cows this side of India, Ben Jerry s has them. With a solid policy of using cream only from farms who have pledged not to use BGH (bovine growth hormone), Ben Jerry s provides you with a non-toxic product. All their cream comes from local Vermont family farms. This ensures that profits stay in the community, something that large corporations as a whole fail to do. 

The first ice cream factory in the U.S. was established in 1851 in Baltimore, MD, by Jacob Fussel. The ice cream soda was introduced in 1879 at the Centennial Exposition in Philadelphia. The ice cream cone was introduced at the Louisiana Purchase Exposition in St. Louis in 1904. A quart of ice cream provides about 1170 calories, and a quart of ice milk about 820 calories. The record amount of ice cream eaten by one person is 7 lb, 13 oz in 16 minutes by Archie Leggett, 22 yrs old, of Hamilton, Scotland, on February 9, 1973. 

Brazelton, an employee of Fussell s, a little later, established ice cream plants in St. Louis, Cincinnati, and Chicago. It is interesting to note that J. M. Horton, who died in 1914, bought Fussell s New York ice cream plant. Horton was then a young man of 22. This same ice cream plant was estimated in 1910 at 600,000. Horton left an estate of 4,000,000. These facts give a clear idea of what the ice cream factory of to-day must be to compete in the large city trade. 

Thus colder refrigerants cool faster. The coldest refrigerant available to the Victorians was ice and salt at about — 20°C. Today ice cream factories typically use liquid ammonia at — 30 °C, and ice cream making is much faster. In fact, Newton s law of cooling explains why the world record for the fastest ice cream ever made used liquid nitrogen at —196 °C2 This is demonstrated in Experiment 12 in Chapter 8. 

As the mix passes along the barrel, its temperature decreases, and its ice content increases. As we have seen in Chapter 2, both of these cause the viscosity of the mix to increase the viscosity of the sugar solution increases as the temperature decreases and the solute concentration and the viscosity of the suspension increase as the volume fraction of ice increases. Figure 4.13 shows the ice content (i.e. the mass of ice as a percentage of the total mass) of a typical ice cream as a function of temperature between 0 and — 20 °C. This is known as the ice curve. The ice content of this formulation is 35% when it leaves the factory freezer at — 5 °C and 54% at a typical storage temperature of —18 °C. 

Ice cream is hardened in a hardening tunnel, an enclosed chamber into which the ice cream passes on a conveyor belt from the factory freezer. Inside, cold air (typically —30 °C to —45 °C) is blown over the ice cream. The lower the air temperature, and the faster the air flow, the faster heat is removed from the ice cream. Air turbulence also increases the rate of heat transfer. The chamber is enclosed to minimize exchange of cold air inside the system with warm ambient air, and so to reduce the build up of frost that would reduce the efficiency. Cold stores, which are typically about — 25°C, are not suitable for hardening because they are not cold enough and have still air, so they cannot cool the ice cream rapidly enough to minimize recrystallization. 

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