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ELECTROMAGNETIC SPECTRUM

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Radio and TV waves are so weak (105 to 109 cycles per second) that they need metal antennas to speed up their movement in order to be transmitted or received. Microwaves are strong enough (109 to 1011 cycles per second) to affect polar molecules (like water), and since most food is largely water, microwaves can be used in cooking. Infrared heat (1011 to 1014 cycles per second) is the only section of the spectrum that feels hot; the waves in this section are strong enough to melt fat, coagulate protein, caramelize sugar, and gelatinize starch, as well as boil water. Visible light is stronger (1014 to 1015 cycles per second) than heat radiation; it is powerful enough to change the pigments in our skin and cause fats to become rancid. Ultraviolet rays (1015 to 1018 cycles per second) can burn our skin, damage our DNA, and cause the development of malignancies. X-rays and gamma rays (more than 1018 cycles per second) ionize molecules by stripping electrons from them; they are strong enough to kill microbes, making them a useful form of radiation in industrial sterilization processes.

Visible light (the only form of radiant energy that we can see) occupies a small area of the spectrum and can be divided into seven wavelengths, which appear to our eye as different colors; red is the weakest and violet is the strongest. Radiant heat energy that is weaker than visible light is called infrared (below red). Ultraviolet (beyond violet) is what we call radiation that is stronger than visible light. The colors of fire correspond to this energy spectrum, ranging from orangey red to blue-violet. Obviously, flames are visible, but we have already said that radiant heat is invisible. Does that mean that fire isn’t really hot? Sort of. The colorful parts of a flame are stronger forms of radiant energy than the invisible heat rising from them, but the area of heat surrounding a flame is hotter than the flame itself.

Although the principles of conduction, convection, and radiant heat help us to understand how grilling works, in actual practice these principles are not as clear-cut. They all occur simultaneously. The flow of heat from fire to grill grate is radiation. The heating of the grate itself is conduction. The heating of the food’s surface is a combination of conduction from the grill grate, radiation from the heat flowing between the bars of the grate, and convection of the air around the food (especially when the grill is covered). As heat moves through the interior of the food, it is being transferred from one molecule to another by conduction and by convection as heated juices begin to circulate through the ingredient. To visualize these principles at work, see the illustration below.

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1. Convection

2. Conduction

3. Radiation

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Most grilling techniques were developed long before the science of heat transference was understood. But even a basic understanding of the science behind cooking food over an open flame will help you to master the techniques of grilling.

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C. Mastering Grilling Techniques

Grilling and barbecuing are two distinct methods of dry-heat cooking. Grilled food is cooked quickly over direct, high heat. Barbecued food is cooked slowly via indirect, low heat with plenty of smoke. Several other grilling methods fall somewhere between these two extremes, including indirect grilling, rotisserie grilling or spit-roasting, smoking on a grill, and grilling right on the coals. Here’s how to master each technique.

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A HOT, CLEAN, WELL-OILED GRILL

Think of your grill grate as an open sauté pan. Just like a sauté pan, it should be clean, hot, and lubricated before adding any food. A hot, clean, well-oiled grill gives you the best browning, deepest grill marks, and purest flavors.

Preheating. A hot grill grate helps to sear foods and create deep grill marks. It also prevents sticking. We recommend preheating the grill grate for at least 10 minutes on high heat, preferably with the