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Cooking with Chemistry: Understanding how your pots, stoves handle heat in your kitchen

(Claire Sun/Daily Bruin)

By Jack Tulyag

Feb. 27, 2019 8:11 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.

A chef is more than someone who combines certain ingredients in a certain order – a true chef is a master of thermodynamics.

The science of heating plays such a prevalent role in cooking that it can contribute to how food is described: steamed eggs, grilled onion, seared steak. The methods used in cooking are combinations of the three basic ways of heat transfer: conduction, convection and radiation.

Click, click, click.

A natural gas stove releases of a mixture of gases, mostly methane. That click you hear when you turn on the burner is the continuous discharge of a piezoelectric crystal, which is basically constant sparks of electric charge emitted into the air. A nice flame erupts in less than a second and you are ready to cook.

Such a process seems so ordinary to us, but producing fire is fascinatingly complex. The mechanism relies on some fuel source, an energetic kick and an oxidant. An oxidant is a unique type of chemical that is capable of robbing an electron from other molecules, typically forming an unstable molecule known as a free radical. But hold on, where was the oxidant in our natural gas stove? Here’s a hint: It’s in the name.

Oxygen, in fact, is the most common oxidant we encounter. The spark generated by squeezing a crystal provides enough energy to destabilize the oxygen in our atmosphere. That excited oxygen crashes into the unstable methane floating around, which in turns creates an unstable free radical, bumping into its neighboring methane molecules.

This ultra-fast chain must eventually stop, but not before it releases light and heat. The fire we observe is not necessarily a definitive thing – it’s light that is released from a reaction that we just so happen to be able to see.

Radiation – No, not the nuclear kind

Radiation is one way for heat to be transferred. If you’re roasting a pig on a spit, you are relying on electromagnetic waves produced by the flame to cook the pig. What is going on when light interacts with the matter?

The specific answers to such a question led to tremendous advancements in the field of physics in the 1900s, but what we care about is that matter basically absorbs light in a very particular manner. The absorbed light must be released in some way. For cooking, what this means is that the extra energy goes into the molecular vibrations of your food, generating thermal energy.

Picking your pots and pans

Convection and conduction are two aspects of the same thing: motion. When electromagnetic waves radiate and are absorbed by matter, it’s the resulting jiggle of the molecules that we know as heat. Convection refers to heat transfer in fluids and conduction in solids.

For a natural gas stove, convection heats the bottom pan of a skillet, allowing for conduction between the skillet and the food. Quality thermal conduction relies on molecules in a solid moving together in synchronized motion. If the material is defective, the motion may be random and not conduct well.

The surface of food heats first, as one would expect. The trick in cooking is to make sure the insides cook just as well.

So what makes for an adequate skillet? Two things: the abilities of a skillet to distribute and retain heat well. Distribution relies on good thermal conduction, so metals without many defects are best. But what about retention?

Retention is referred to as an object’s heat capacity – basically how much thermal energy it can store. The key property that determines this is how much stuff is in the material. If it’s super dense, then it can retain a lot of its heat, while if not, it’s going to dissipate it very quickly.

If you’ve ever been to a Korean restaurant, you may have been served food in a granite bowl. This material has a massive heat capacity and retains so much heat that it will still be cooking your food when they serve it to you.

Stainless steel is dense but it has a lot of impurities in it due to alloying. Hence, it conducts heat poorly but is fantastic at retaining it. Aluminum is a great conductor of heat since it’s a pure metal, but it is light and cannot retain its heat well. Laminated pots, a sheet of aluminum in between two sheets of stainless steel, are very common as they combine both properties. A fantastic metal to use is copper, due to its high density and great thermal conduction, but these properties are what makes it more expensive than others.

Electric or gas?

So far, we have been neglecting those who may use electric stoves. There is nothing wrong with this, after all, heat is heat. Why do so many chefs prefer using gas stoves instead?

Electric stoves tend to lack the precision of natural gas stoves, making the control of heat transfer more difficult. An electric stove tries to pump electricity through a highly resistant material, thus generating heat and then immediately conducting into the pot. However, this takes a while compared to the almost instantaneous burst of flame. Quickly adjusting the temperature is a bit of a challenge as well. For a flame, it’s a quick turn of the knob. For the electric stove, it’s the quick turn of a knob plus the wait for the heat to dissipate off the coils.

Control of the oven is absolutely vital to a chef. Using the right ingredients at the right time is important, but the true art of cooking involves mastering heat. This is more than just the food – it’s also making sure the chef has the right tools at hand.

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