Olive Dunn, age 8, of Laconia, N.H., for her question:
HOW IS ICE CREAM MADE?
Although some people enjoy making ice cream at home, almost all ice cream is made by commercial manufacturers. At home'or in an ice cream factory, three chief in ingredients are combined: milk solids, sugar water.
In an ice cream plant, the mix is stirred in a large vat and then pasteurized. Next, the mix is homogenized, a process that breaks down the fat particles. Homogenizing the mix helps give ice cream a smooth texture.
The mix is then pumped through a cooler where its temperature drops to about 35 degrees Fahrenheit. Then it is put into a storage tank for three or four hours to settle. Flavorings and colorings are added, and then the mix is frozen.
Most commercial freezers use liquid ammonia to maintain a temperature of about minus 22 degrees Fahrenheit. The mix freezes against the size of the freezer,, which has fanlike blades that rotate at a high speed.
The blades scrape the frozen mix from the sides of the freezer and whip air bubbles into it. If air were not added, eating ice cream would be like chewing sweetened ice cubes. The air bubbles increase the volume of the mix.
The difference in volume before and after air is added is called overrun. Ice cream packaged for home use has about 90 percent overrun.
Sherbet has about 35 percent overrun. Fruit and nuts may be added to ice cream before it is packaged. After packaged, the product is placed in a hardening room. Hardening takes at least 12 hours at temperatures ranging from minus 10 degrees to minus 20 degrees Fahrenheit.
No one knows when ice cream was first made. In 1295, the Italian trader Marco Polo returned to Europe from China and may have brought receipes for water ices. During the 1600s, Europeans used a combination of ice, snow and a mineral called saltpeter to freeze cream and fruit.
English colonists probably brought recipes for ice cream to America in the early 1700s. Ice cream became a popular luxury food, but almostall of it was made at home until 1851 when John Fussell, a Baltimore milk dealer, established the first ice cream plant.
Ice cream became a national favorite during the early 1900s after soda fountains introduced sodas, sundaes and other new ways of serving it. Ice cream cones were first served at the World's Fair in St. Louis in 1904. The ice cream bar came along in 1921.
Ice cream production increased a great deal during the late 1940, following World War II. During the 1970s, the United States produced over 775 million gallons of ice cream each year.