Cooking with Chemistry: Choosing the right oil for perfectly fried chicken
(Kyle Icban/Daily Bruin)
By Jack Tulyag
Oct. 2, 2019 5:33 p.m.
Chemistry as a science sounds like something that should strictly be confined to a laboratory with poisonous toxins and exploding reactions, but, as it turns out, most labs aren’t quite like that. In fact, the most important laboratory is found in every home: the kitchen. Understanding the complex processes that go on in the kitchen allow us to go further than the recipe to improve our cooking.
Southern fried chicken sits on the pedestal as one of America’s greatest foods for a good reason: It just tastes so good.
The key to this classic dish relies on understanding what dropping meat into a hot bath of oil does: The act of deep-frying involves the rapid dehydration of meat and the corresponding interaction with oil and water in the meat. As it turns out, choosing the right oil for the job is absolutely essential.
Deep-frying is an excellent example of the diverse chemical reactions that result from simple actions like dipping chicken into hot oil.
Oils are fats, meaning they are all generally long threads of carbon. There are small variations that can classify fats into a diverse group of categories. These include saturated vs. unsaturated and trans vs. cis fats, some of which are typical identifiers listed on the nutrition facts of most foods.
These names actually refer to the structure and chemical properties of the fat. For example, saturated fats are completely, well, saturated with hydrogen atoms. Unsaturated fats, on the other hand, have some extra space for hydrogen atoms.
While the distinction between the two may seem inconsequential, this results in dramatic differences in how the molecules interact with each other. Saturated fats are solid at room temperature but most unsaturated fats are liquid – think butter vs. vegetable oil. Having a few less hydrogen atoms leads to less interactions between molecules and an overall weakly bound soup of molecules.
Having a fewer number of hydrogen atoms also means that the oils are more prone to reacting, predominately with oxygen and water. Under a hot environment, there can be a number of uncontrolled chemical reactions that break down the oil into smaller molecules, eventually small enough that they become airborne and lead to that characteristic oil smell.
Selecting the oil is the most important aspect of frying chicken, and this goes back to the overall structure of the molecule. If the fat is way too saturated, it results in a waxy layer coating the meat. This is due to the solidification of the aforementioned saturated fats. Too little saturation, and reactions cannot induce quality crisping. The best oil is one in between: namely, peanut oil.
The hot temperature means the oil is a huge heat bath, quickly dehydrating the meat. The hissing and spurting of oil is the water within the chicken boiling and escaping. The oil then takes the place water inside the food. The water that escaped the food can do two things: It will either escape as steam or it will react with the oil and break it down into smaller carbon molecules.
At the same time, the batter and breading bits that fall off the surface of the chicken lead to undesirable chemical reactions, making the oil an even bigger mess of molecules.
To facilitate heating, the chicken has to be dry before being dunked into oil. Otherwise, too much water is introduced, breaking down the oil. The batter surrounding the chicken is equally important, not just for the crunchy brown skin but to prevent the meat from heating too much and becoming tough.
So what good is used oil? It’s actually very useful – the best oil to use for fried chicken is the slightly used kind. If you have some extra old oil, add a tiny bit into a new batch. A brand new batch of oil is rather pure, and as a result will hate water.
While the water steams off, there tends to be a bubble of water forming around the chicken as the whole thing fails to mix. This is a problem because the meat cannot heat at an adequate pace. If a small amount of used oil is mixed with the fresh, then this introduces a significant amount of molecules that are capable of mixing oil and water with one another.
Chefs has to take care of their tools, which partly involves making sure the oil never gets above its flash point, i.e. sets on fire, and removing all the little bits of food from the oil. That way, it can be used many more times. Storing used oil in a cool, dark place will prevent additional reactions from occurring in the meantime.
Fried chicken, though simple to cook, is a beautiful example of the complex balance needed to produce the best food. Understanding the right type of oil to pick and why it works ultimately leads to better-tasting fried chicken.