Wednesday, February 14, 2007

Ice cream

Before the growth of modern refrigeration, ice cream was a luxury item kept for special occasions. Making ice cream was quite difficult. Ice was cut commercially from lakes and ponds during the winter and stored in large heaps in holes in the ground or in wood-frame ice houses, insulated by straw. Ice cream was made by hand in a huge bowl enclosed by packed ice and salt. The temperature of the ingredients was reduced by the mix of compressed ice and salt. The salt water was chilled by the ice, and the action of the salt on the ice causes it to (partially) melt, absorbing latent heat bringing the combination below the freezing point of pure water. The wrapped up container can also make better thermal contact with the salty water and ice mixture than it could with ice alone.The hand-cranked churn, which still used ice and salt for cooling, was made-up by an American named Nancy Johnson in 1846, making invention possible on site and avoiding the problem of nonstop chilling between production and consumer. Ice cream became a trendy item for the first time. The world's first business ice cream factory was opened in Baltimore, Maryland in 1851, by Jacob Fussell, a dairy farmer. An unstable demand for his milk led him to mass create ice cream. This allowed the previously expensive invention to be offered in the city at reduced prices.Fussell opened ice cream parlors as far west as Texas. Many were still around well into the twentieth century. Fussell later sold his business to Borden.
The improvement of industrial refrigeration by German engineer Carl von Linde during the 1870s eliminated the need to cut and store natural ice and when the continuous-process freezer was perfected in 1926, allowed commercial mass invention of ice cream and the birth of the modern ice cream industry.The most common method for producing ice cream at home is to use an ice cream maker, in modern times normally an electrical device that churns the ice cream mixture while cooled inside a house freezer, or using ice and salt. A newer method of making home-made ice cream is to add liquid nitrogen to the mixture while moving it using a spoon or spatula.