Sciences Participating with Arts & Culture in Education

For Best Results, Stick it in the Fridge

Illustrated by Julie Nguyen

Your mom comes home with a couple of nice, juicy, succulent steaks for next week’s holiday dinner. In order to keep them for a whole week, just as tasty and appetizing as they look to you, your dad, and your dog Sparky, imagine that she has to cover them in salt or spices, dehydrate them in the sun, smoke them, candy them, or even pickle them.

Picture doing your homework at the kitchen table with the week-old spiced steaks stinking up your whole house: Yeah, right!

Before the technology for your refrigerator was developed, this is what you would have gone through to have a nice, home cooked meal without your food spoiling. Lucky for you, a series of food preservation methods have been tested, rejected, and improved until today, where most of the world’s food preservation comes from refrigeration and freezing.

Spoilage can be defined as any change in the food that renders it unfit for human consumption [i] (Sparky might still be able to get away with eating it). This can be caused by certain physical or chemical changes in the constituent molecules of food, including degradation by enzymes, tearing of tissues in the food, or more importantly, being contaminated by bacteria, and moulds[ii].

In order to avoid this spoilage, different methods can be used to either slow down the activity of these bacteria, yeasts, moulds, or kill them altogether. Chemical reactions will be hard to stop completely, but certain conditions will slow them to avoid premature food spoilage.

Many years ago, the primary way to conserve food was mainly sun-drying foods, as the lack of water would slow chemical reactions and decrease the activity of micro-organisms (bacteria, moulds, etc.) in the food. Other ways of doing so consisted of salting, pickling, and using sugar in jams and fruit marmalades. Spices were thought to be a means of food preservation, but really they just masked unpleasant tastes [iii].

The above methods became relatively dated and impractical, and the development of a completely new and revolutionary method of food preservation came to be: refrigeration and freezing.

Refrigeration is the process of removing heat from an enclosed space, or from a substance, to lower its temperature [iv]. The way refrigerators today work is by a rapidly expanding gas (the refrigerant), which cools as it expands. This cooled gas passes through coils next to the refrigeration compartment and, as it goes by, sucks the heat out of the compartment, resulting in a lower temperature in the fridge.

Storage at low temperatures prolongs the shelf life of foods. In general, low temperatures reduce the growth rates of microorganisms and slow many of the physical and chemical reactions that occur in foods [v].

In freezing, the physics of cooling the compartment is quite similar, but the sub-zero temperature converts much of the water in certain foods into ice. This freezing must be done quickly in order to avoid detrimental changes in the properties of the foods [vi]. Although the technology was invented about 200 years ago, freezers and refrigerators have gone through many difficulties on the way to the safe and easy-to-use design of today’s society.

The first practical refrigerating machine was built by Jacob Perkins in 1834. The cooling gas that Perkins used was a volatile liquid known as ether (also used by doctors 150 years ago as a medical and dental anesthetic) [vii]. Early models of the refrigerator also used toxic gases such as ammonia, methyl chloride, and sulfur dioxide as refrigerants, until cases of leaking in the gas chambers caused death in the 1920s. These gases were replaced with Freon, a gas now classified as a chlorofluorocarbon (CFC). Only decades later was it discovered that these CFCs are partially responsible for the depletion of the world’s ozone layer. Hydrofluorocarbons (HFC) and, more recently, carbon dioxide (CO₂) have now completely replaced these dangerous gases in our refrigerating systems [viii].

Food can be preserved in many different ways, from ancient salting and smoking, to futuristic freeze-drying and the use of radiation to sterilize foods, but when it comes down to practicality, the widespread refrigerator and freezer you go to for your everyday snacking takes the cake. Sparky will be happy to know that the science behind your refrigerator will keep his steak nice and fresh, all week long.
 

Endnotes

i "food preservation." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 14 Oct. 2009 <http://www.britannica.com/EBchecked/topic/212684/food-preservation>.

ii Handbook of food engineering practice. Boca Raton, Fla: CRC, 1997. Google books. Web. 14 Oct. 2009. <http://books.google.ca/books?>

iii "Food Preservation – Dictionary definition of Food Preservation | Encyclopedia.com: FREE online dictionary." Encyclopedia - Online Dictionary | Encyclopedia.com: Get facts, articles, pictures, video. Web. 18 Oct. 2009. <http://www.encyclopedia.com/doc/1G2-3401801549.html>.

iv "The History of the Refrigerator - and Freezer." Inventors. Web. 14 Oct. 2009. <http://inventors.about.com/library/inventors/blrefrigerator.htm>.

v "TLC Cooking "How Food Preservation Works"" TLC Cooking "Food and Recipes" Web. 18 Oct. 2009. <http://recipes.howstuffworks.com/food-preservation.htm>.

vi "TLC Cooking "How Food Preservation Works"" TLC Cooking "Food and Recipes" Web. 18 Oct. 2009. <http://recipes.howstuffworks.com/food-preservation.htm>.

vii "The History of the Refrigerator - and Freezer." Inventors. Web. 14 Oct. 2009. <http://inventors.about.com/library/inventors/blrefrigerator.htm>.

viii"The History of the Refrigerator - and Freezer." Inventors. Web. 14 Oct. 2009. <http://inventors.about.com/library/inventors/blrefrigerator.htm>.