Kristine Nolin, University of Richmond
Frying a turkey is a great way to get a delicious, chewy Thanksgiving meal. But this method of cooking can be a very dangerous endeavor.
Every fall, millions of dollars in damage, trips to the emergency room, and even deaths result from attempts to fry turkeys. The vast majority of these accidents happen because people put frozen turkeys in boiling oil. If you are planning to fry this year, be sure to thaw and dry your turkey before putting it in the pot. Failure to do so can lead to explosive disaster.
What’s so dangerous about putting even a partially frozen turkey in a deep fryer?
I am a chemist who studies plant, fungal and animal compounds and I love food chemistry. The reason why frozen turkeys explode, basically, has to do with differences in density. There is a difference in density between oil and water and differences in density of water between its solid, liquid and gaseous states. When these density differences interact in the right way, you get a blast.
Density is the weight of an object for a specific volume. For example, imagine you have an ice cube in one hand and a marshmallow in the other. While they are roughly the same size, the ice cube is heavier – it is denser.
The first important density difference in frying is that water is denser than oil. It has to do with the narrowness of the molecules of each substance and the weight of the atoms that make up each liquid.
Water molecules are small and pile up tightly. The oil molecules are much larger and do not stack together as well in comparison. Additionally, water is made up of oxygen and hydrogen atoms, while oils are mostly made up of carbon and hydrogen. Oxygen is heavier than carbon. This means that, for example, a cup of water has more atoms than a cup of oil, and these individual atoms are heavier. This is why the oil floats above the water. It’s less dense.
While different materials have different densities, liquids, solids, and gases of the same material can also have different densities. You observe it each time you place an ice cube in a glass of water: the ice floats upwards because it is less dense than water.
When water absorbs heat, it switches to its gas phase, vapor. Steam occupies 1,700 times the volume of the same number of molecules of liquid water. You see this effect when you boil water in a kettle. The force of the expanding gas pushes the steam out of the kettle through the whistle, causing the squealing sound.
Frozen turkeys are filled with water
Frozen turkeys – or any type of frozen meat, for that matter – contain a lot of ice. Raw meat can contain 56% to 73% water. If you’ve ever thawed a frozen piece of meat, you’ve probably seen all the liquid coming out of it.
For deep frying, the cooking oil is heated to about 350 degrees Fahrenheit (175 C). This is much hotter than the boiling point of water, which is 212 F (100 C). So when ice from a frozen turkey comes in contact with hot oil, the surface ice quickly turns to vapor.
This rapid transition is not a problem when it occurs on the very surface of the oil. Steam escapes harmlessly into the air.
However, when you dip a turkey in oil, the ice cream inside the turkey absorbs the heat and melts, forming liquid water. This is where density comes into play.
This liquid water is denser than oil, so it falls to the bottom of the pot. Water molecules continue to absorb heat and energy and eventually change phase and become vapor. The water molecules then quickly separate from each other and the volume increases 1700 times. This expansion drops the density of water to a fraction of one percent of the density of oil, so the gas wants to rise to the surface quickly.[More than 140,000 readers get one of The Conversation’s informative newsletters. Join the list today.]
Combine the rapid change in density with the expansion of volume and you have a blast. The steam expands and rises, blowing the boiling oil out of the pan. If this were not dangerous enough, when the displaced oil comes in contact with a burner or flame, it can ignite. Once oil droplets catch fire, the flames quickly ignite nearby oil molecules, causing a rapid and often catastrophic fire.
Every year, thousands of accidents like this happen. So if you do decide to fry a turkey for Thanksgiving this year, be sure to thaw and dry it well. And the next time you add some liquid to a pot full of oil and find yourself with oil all over the stove, you’ll know why.
Kristine Nolin, associate professor of chemistry, University of Richmond
This article is republished from The Conversation under a Creative Commons license. Read the original article.