Ice cream makers

Note To make the sorbet, place 1 cup Champagne, 1 cup elderjlower syrup and 1 cup water in an ice cream maker and freeze according to instructions. 

Place all ingredients into a chilled ice cream maker and process. 

You may be familiar with the property illustrated in the first demonstration, freezing-point depression, if you have ever used an ice cream maker. In ice cream making, the cream mixture is poured into a container and the container is placed in a bath of salted ice. The salt-ice mixture cools to a point below the freezing point of water, so when the water in the cream comes into contact with the sides of the container, it freezes. A paddle to scrape ice crystals off the sides of the container is turned constantly until the cream and ice form a uniform semisolid. The fi eezing point of the salt-ice mixture is lowered because of the presence of a dissolved solute (salt) in the solvent (water). Antifreeze works on the same principle. Chosen to be noncorrosive, antifreeze is a material added to radiator water to lower the freezing point so the radiator water will not readily freeze. 

To make ice cream at home without an ice cream maker. 

To see a scraped surface heat exchanger in operation. Domestic ice cream makers work on the same principle as factory freezers, but since they do not operate under pressure you can see what happens inside. 

Ice cream mix, e.g. from Experiment 8 Domestic ice cream maker... 

Simply make the ice cream according to the ice cream maker s instructions, and then compare the results with the other methods, as described in Experiments 14-16 below. 

Have you ever wondered why salt is added to ice in an ice-cream maker Or why salt is scattered on icy roads in cold climates Salt actually lowers the melting point of ice. A salt-and-water solution will remain a liquid even below 0 °C. By adding salt to ice in the ice-cream maker, you form a mbcfure of ice, salf, and wafer fhaf can reach a temperature of about —10 °C, cold enough to freeze the cream. On the road, the salt allows the ice to melt, even if the ambient temperature is below freezing. 

Salt is often added to ice in ice-cream makers and is used to melt ice on roads in frigid weather. The salt lowers the freezing point of water, allowing the cream within the ice-cream maker to freeze and the ice on icy roads to melt. Antifreeze is used in the cooling systems of cars both to lower the freezing point of the coolant in winter and to raise its boiling point in summer. 

Nuts and seed offer the widest choice of oils where the physical condition of the oil is important. Nut oils vary from very solid coconut and palm oils to very liquid canola, safflower and sunflower oils. Thus confectioners, bakers, salters, ice-cream makers and snack food manufacturers have a choice of nut oils to fulfill their needs. A single manufacturer of cookies, wafers, tea cakes, sandwich fillings, fruit cakes, layer cakes and pancake mixes has a choice of oils that meet the particular needs. Nuts and oily seed having the highest oil content are least stable. Schley cultivar of pecans, with 68% oil, is less stable than cultivars containing less oil. The iodine value, which measures the degree of unsaturation of the oil is used commercially as a means of predicting shelf-life. The ratio of oleic to linoleic acids is also a measure of oil stability. 

In an ice cream maker, salt is used to lower the freezing point of water. The cold salt-ice—water slurry reaches temperatures of — 10"C, causing the ice cream to solidify. 

What mass of salt (NaCl) should you add to 1.00 L of water in an ice cream maker to make a solution that freezes at —10.0 °C Assume complete dissociation of the NaCl and density of 1.00 g/mL for water. 

This method relies on the same science as the ice cream hall (see Machine-Made The World of Ice Cream Makers, facing page), that is, the chemical reaction between rock salt and ice that quickly freezes the ingredients. This method is so simple that kids can do it, and the time involved from start to finish is about 10 minutes. 

Figure 6.2 Ice cream maker. The handle rotates an inner cylinder. As cream between the rotating inner cyhnder and the fixed outer cylinder turns into ice cream, its viscosity increases and the crank gets harder to turn. The inset shows the geometry of a viscometer for measuring fluid viscosity. It consists of two closely spaced cylinders, one of which is fixed and the other of which can rotate. With a narrow gap between the cylinders this geometry is similar to the plates shown in Figure 6.1.

Salts, such as NaCl, can be used to prepare a slush bath, a mixture used to cool or freeze something. One example is the mixture of ice and NaCl(s) used to freeze ice cream in a home ice-cream maker. Because the slush bath is at a temperature well below 0 °C, it is easy to freeze the sugar-and-milk mixture that makes up the ice cream. NaCl is also useful for deicing roads. It is effective in melting ice at temperatures as low as —21 °C (-6 °F). This is the lowest freezing point of a NaCl(aq) solution. 

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