To a large extent, cooking is about applying heat to your dishes, which allows you to incorporate their ingredients, cook them through, and—as is the case with red meat, poultry, and seafood—make them safe to eat.
Heat in its simplest form is thermal energy. As some of you may remember from high school physics, the law of energy conservation states that energy in the universe can neither be created nor destroyed. Instead, it can only be converted from one form to another.
So cooking is mostly about heat transfer, which you can achieve in various ways. When it comes to your home kitchen, these ways are typically conduction, induction, convection, and radiation.
Heat transfer is one of the first things they teach up-and-coming chefs at culinary school.
As home cooks, understanding heat transfer is essential to selecting the best appliances for our kitchens and to preparing the most delicious and well-textured foods for ourselves and our families.
This is why, in this post in my “Cooking Skills” series, I will give you a crash course on heat transfer.
When you transfer heat from the flame on your gas stove or the coils on your electric range to your pans and pots, you’re using conduction.
Conduction, in other words, is the process of thermal transfer between a hot object and a neutral object when they come in direct contact with each other.
Here’s how it works:
First, you put a cooking vessel in direct contact with a cooking appliance. Then, you turn up the dial on that appliance, igniting a flame or bringing a coil up to heat. Slowly but surely, the cookware picks up the heat until it gets hot enough to cook in.
Conduction cooks food from the outside-in, so, when cooked correctly, your meats and vegetables will come out crispy on the outside but juicy on the inside.
It’s ideal for cooking methods like searing, sautéing, and pan-frying, which help you achieve an aromatic and flavorful browning on your foods thanks to the Maillard reaction.
As cooks, we usually add vegetable oil or animal fat to our pans and pots. The oil or fat—like when you pan-fry ribeye in a lightly greased skillet or sauté mushrooms in a bit of olive oil—not only carries flavors but also assists in the transfer of heat.
Conduction cooking’s effectiveness depends first and foremost on the thermal conductivity of your cookware. Metal cookware is so prevalent because, as a material, metal is thermally conductive compared to glass or stone.
But, when it comes to their ability to conduct and hold on to heat, not all metals are created equal.
Copper and aluminum are excellent conductors of heat. They make for cookware that heats up evenly and responds quickly to sudden changes in the heat dial.
Cast iron and stainless steel, on the other hand, are poor conductors of heat. They take much longer to heat up as a result. But they can hold on to that heat exceptionally well once they do.
Copper and aluminum cookware are best for à la minute recipes like fried eggs or delicate foods like fish fillets. Cast iron skillets and stainless steel frying pans brown foods fantastically and keep your dishes warm for hours.
One way to think of copper and aluminum cookware is as Japanese cars. In turn, their cast iron and stainless steel counterparts resemble American SUVs.
Both have their pros and cons, and—depending on your capacity needs and style of driving—you may prefer one or the other.
Induction is when an induction cooktop contactlessly induces heat to your pans and pots.
Induction ranges have no flame burners or heating elements. Instead, they work by running alternating electrical current (AC) through copper coils under each of their cooking zones, which creates an oscillating magnetic field above it.
Pans and pots that contain iron pick up that magnetic field and get charged with an eddy current. That eddy current causes the electrons inside them to vibrate so intensely that the friction from their movement heats your cooking vessel almost immediately.
Many people get intimidated by the science behind induction cooking. But, at the end of the day, induction is nothing more than a more recent and efficient heat transfer method than conduction.
Induction cooktops are incredibly efficient, so cooking with them is faster. On average, it takes 25% to 50% less time to cook on an induction stove than on gas or electric (as estimated by HowStuffWorks).
However, not all pans and pots work with induction ranges. All of your cookware needs to be ferromagnetic.
“Ferromagnetic” means that a cooking vessel must contain enough iron for a magnet to be able to stick to it. So the easiest and most accurate way to test if your current cookware is induction-friendly is to put a magnet under it—and see if it sticks.
This makes copper, aluminum, and stainless steel pans and pots incompatible with induction by default. To make them induction-friendly, most manufacturers add a magnetized disc-bottom or core to them.
Convection is the transfer of heat to your food through hot air or liquid.
When you turn your oven on, the heating panels get hot, which heats the air that’s sitting closest to them. That air becomes less dense, rises to the top, and gets replaced by denser and cooler air. This process repeats on and on, forming a steady flow of air called a “convection current.”
This is how regular ovens work. There are also convection ovens, which have a fan-and-exhaust system that hastens and improves their airflow, cooking your foods faster and more evenly.
When in doubt, get a convection oven. Of course, if a recipe requires it, you can always turn the fan on or off and use it like a regular oven. Still, you’ll be cooking fan-on 99% of the time, which yields greater outcomes.
Baking works best when room-temperature goods come into sudden contact with the intense heat of a preheated oven. Preheating your oven promotes browning and causes baked goods to puff up, so remember its role and don’t forget to do it.
When time permits me to do so, I try to preheat my oven to the desired temperature for at least 30 minutes. This is especially important when I’m about to bake loaves of bread and pizza pies on a baking stone.
Similar processes happen, but to the liquid rather than gas, when you bring a pot of water to a boil.
Depending on the type of cooktop you have, conduction or induction heats the pot, which warms the water molecules sitting closest to the bottom. Then, convection currents come into play—the warm water rises to the top, gets replaced by cooler water, which warms up, gets replaced, and so on, and so on.
When you dip eggs or pasta into boiling water, you’re making use of the convection currents inside it to cook them. The force from the convection currents is also what makes some foods, like ravioli, float.
There’s no need to cook all of your foods on a rolling boil (or “full boil,” as some readers may know it). But before dipping them into the water, make sure it’s hot enough, or it will be very hard for you to time your cooking. When in doubt, use a meat thermometer.
Radiation is the process of heating foods through waves of energy that travel through space and hit it. There are several types of radiation, but the two types that matter when it comes down to cooking are infrared radiation and microwave radiation.
Infrared radiation is when the infrared light, emitted naturally by the burning wood or glowing charcoal of an outside grill, or artificially by the heating panel of your broiler, toaster, or infrared oven, heats both your cookware and your food.
A cast iron skillet or Dutch oven is better-suited for infrared cooking than a white porcelain casserole because—unlike the light-colored and smooth-surfaced casserole dish—it’s pitch-black and porous.
Glass also makes for excellent bakeware for infrared cooking because it allows some infrared light to pass through, hitting the surface of the food inside it and therefore cooking that food faster.
For best results with infrared cooking, use non-enameled cast iron, dark-colored carbon steel, anodized aluminum, or glass bakeware.
Microwave radiation is when microwaves produced by a generator (an electron tube called a “magnetron”) inside your microwave oven penetrate your food and cause the water molecules inside it to vibrate. The friction that comes from their vibration causes the food to heat up.
This is the reason why, when microwaved for the same amount of time and on the same setting, high-moisture foods will heat up much quicker than low-moisture foods.
In a way, microwave radiation is similar to induction cooking. Compared to it, it’s more direct: instead of inducing vibrations in the electrons inside your cookware, it causes the water molecules in the food to vibrate.
Since microwaves can penetrate your foods deeply, small batches of food cook quickly and from the inside out. Big batches, however, tend to take longer—and will come out overly dry.
Also, a microwave oven won’t promote browning by triggering the Maillard reaction, which is what makes most foods so aromatic and flavorful. So they’re great for thawing or reheating foods, less so for cooking them.