Bacteria are usually the cause of food decay, but they can't grow as well or at all in freezing temperatures, which are at 32 degrees Fahrenheit (0 degrees Celsius) or lower. So, food spoils more slowly if you lower the liquid inside it -- the water molecules -- to freezing temperatures.
As scientists in the early 1800s made related discoveries about the nature of temperature and the laws of thermodynamics, it was then that the framework for artificial temperature regulation fell into place.
American inventor Jacob Perkins built upon the vapor absorption ideas set forth by inventor Oliver Evans in the early 1800s to create a cooling unit that relied on vapor compression, which we'll take a closer look at on the next page [source: Elert]. Perkins determined that a substance used as a refrigerant would absorb and give off heat as it went through pressure changes and transformed from liquid to vapor and back. In other words, Perkins discovered that certain chemicals could lower air temperatures by absorbing all the heat. He obtained the first known patent for a refrigerating unit, but his invention never saw commercial success.
In the late 1840s, a doctor from Florida patented a device that pressurized and then depressurized refrigerant enough to create ice, although it leaked and didn't always work properly. And n 1860, French inventor Ferdinand Carre improved on vapor compression technology by using a more stable and effective (but toxic) refrigerant -- ammonia -- instead of the ether Perkins had used [source: Chapel].
By the 1920s, the technology had been refined enough -- and electricity widely available enough -- that crude but expensive freezers were commercially available in the U.S. and Europe, although they were still widely inefficient. Outside air would seep into the freezer compartment, so they had to be stored in ice houses for better temperature control.
Freezers have improved considerably since then, with more elaborate machinery, better chemicals and more efficient ways of keeping the cold air inside. Read the next page to learn more about how the freezer in your house works.