You’ve probably been doing some barbecuing lately. Approximately 80 percent of U.S. households own a grill or smoker, and the Fourth of July is the most popular occasion to use it, according to a 2013 survey by the Hearth, Patio & Barbecue Association, a trade group. Very few barbecue enthusiasts, however, understand the science behind the char.
When you apply high heat to the surface of meats, vegetables or even dough, a series of fascinating chemical reactions occurs. Understanding them will definitely enhance your street cred at the next neighborhood cookout, and it just might make you a better cook.
The best place to start is not with grilling meats or vegetables, but with the caramelization of sugar — a simpler form of browning reaction.
Anyone who has made a flan has put simple table sugar, or sucrose, over the stove and watched the magic happen. First, it foams, as white granulated sugar melts into a viscous liquid. The liquid goes from relatively colorless, to yellow, to brown. What’s happening? The heat adds energy to the sucrose molecules, breaking them up. Sucrose turns to fructose and glucose. As more energy is added, those molecules break apart further and form new bonds. The result is literally hundreds of different molecules, all from simple sucrose. This molecular variety is why table sugar is a one-note flavor — sweetness — while caramel is an enchanting mixture. Diacetyl adds a buttery flavor. Esters lend a rummy quality. Furans are nutty and maltol is toasty.
It sounds complicated, but, compared with grilling, it’s simple stuff. Sucrose is nothing more than carbon, hydrogen and oxygen. Meats and vegetables bring far more chemical complexity to the party, most importantly amino acids, which contain nitrogen and sulfur. With those new ingredients, the number of flavor compounds in the final mixture increases exponentially.
Grilled meats and veggies contain pyrroles, thiophenes and oxazoles, among many other barely pronounceable chemical mixtures. The combination is so complex that, although French doctor Louis Camille Maillard identified the general form of the reactions more than a century ago, scientists are still working to fully describe the chemical possibilities of the so-called Maillard reactions.
You don’t need to break out a chromatograph at your next cookout to grill a better kebab, but there are a few chemical notes that might be of use to you. The Maillard reactions that make grilled foods interesting don’t start to occur until they reach approximately 230 degrees. That number is important, because the presence of significant amounts of water prevents browning reactions from occurring. As you may remember from beginning chemistry, water boils at 212 degrees. You can keep adding heat to water, but under normal conditions, the temperature will not break that point.
In other words, don’t try to brown a chicken in a steamer. (You probably didn’t need that bit of advice, but now you know the chemical explanation.) More relevant, temperature and moisture control are crucial in grilling. When you apply high heat to a steak or a stalk of asparagus, the moisture in the outer layers evaporates. The temperature of the dehydrated surface of the food can then rise into the Maillard range and brown. Once that happens, the food begins to dehydrate from the outside in. If you begin with a food that is already thin and dry — sliced potatoes, for example — consider grilling over a lower heat to give yourself a margin of error.
There is a small asterisk to this temperature story: Under certain chemical conditions, browning reactions can occur below 212 degrees. Home brewers, for example, know that boiling their wort — a fancy word for pre-beer — deepens the color and heightens the roasty flavor of the barley component. This is because unfermented beer is a syrupy, sweet solution that’s meant to feed sugar-hungry yeast. Concentrated carbohydrates can brown at temperatures lower than 212.
That won’t make much difference to your grilling, except to give you a conversation starter when you decide to crack open a cold one. Here’s a conversation stopper, if you need one. Many medical researchers think some of the chemicals involved in grilling, especially in grilling meats, are carcinogenic.
The link was first suggested with smoked, rather than grilled, foods in the 1960s, when epidemiologists pointed out high rates of stomach cancer in countries where smoked meats were popular. In subsequent decades, as researchers mapped out the chemicals involved, it became clear that smoking wasn’t the only problem. When wood, gas and charcoal burn, they release compounds called polycyclic aromatic hydrocarbons, which have been shown to cause cancer in some lab animals.
That’s bad, but it gets worse. Remember nitrogen, the chemical in meats that helps create those wonderfully diverse flavor compounds through Maillard reactions? When it’s added to polycyclic aromatic hydrocarbons, it seems to enhance their carcinogenic power.
This doesn’t mean you toss your grill and resort to steaming and boiling all of your meals. Many of our activities — driving cars, talking on cellphones, even eating pickled vegetables — have been linked to cancer in varying degrees. Just be aware of the chemistry, as well as the biology, when you decide to fire up your grill.