The thermodynamics of grilling and barbecue

What's all the fuss over infrared? In the past few years a number of gas grills have been touting their superiority because they use "infrared" (IR) heat or they have an IR "sear burner" designed to generate high heat for getting a dark sear on steaks. If you remember your high school science, you know that infrared is a section of the wavelength continuum around us, just down the road from visible light and up the road from the radio in your car. Infrared is a form of radiant heat. Here's how it works: A plate of special glass, ceramics, or metal, sits above the gas burners and below the cooking grates. The plate absorbs the heat and light from the flame and re-radiates it to the food in the form of invisible infrared light rather than warm convection air as do most gas grills. Convection heat energy is much less intense than IR and can be dissipated merely by air currents and short distances. Dr. Greg Blonder, our science advisor explains: "If you warm a plate of steel or special glass or ceramic, the atoms in the plate begin to oscillate. At low temps almost all of the energy is stored as vibrations in the plate. As the plate heats up, the rapidly vibrating atoms cause it to emit IR. Think of it (very loosely) like a bowl of gasoline in a room. At low temps most of the energy is confined to the liquid gas. At higher temps there is so much vibration that the gas evaporates." Max Good, our director of product reviews elaborates: "All IR heat is radiant, but not all radiant heat is IR. IR waves move very fast through the air. The sun radiates intense IR waves which travel great distances at the speed of light without dissipating until they contact solid matter, like your skin, which it warms. The sun also emits other waves, like ultraviolet (UV), which cause sunburn as well as heat. " As another example he says "Consider the IR heaters in warehouses. They are often suspended from the ceiling, but one can easily feel the heat waves standing beneath them. If these same devices were simply conventional gas burners, most of the heat would rise upward." Blonder adds "An oven set on broil is also a radiant heater, with much of the heat is in the near IR, the almost visible section of IR. In principle, a pure IR heater would not be visible to the naked eye, since our eyes can't respond that far out in the light spectrum. In practice, an IR heater glows a dull red, as opposed to a bright red broiler or white hot coals. But they are all radiant heaters." Is IR heating better? Blonder says "IR energy is delivered faster than convection, but slower than conduction. So it can brown a little more effectively than a conventional grill but not as fast as a hot pan or grill grates. There are fewer hot spots from IR cookers. On the other hand, you can get "thermal runaway" with IR. Ff one section of the meat is dark, it absorbs more IR than the lighter sections. Thus browning, and becoming darker still, eventually burning." And real IR burners are not good at achieving low temperatures. We recommend them for getting hot sears on steaks and other meats when the browning of the surface creates thousands of new flavor compounds.

An outdoor cook must be master of the flame and keeper of time Good cooking is the proper combination of heat and time. Your indoor oven has three basic components to control heat and time: A heat source, a thermostat, and a timer. Your outdoor oven, and an oven is exactly what your grill or smoker is, has a heat source, but only a few have a thermostat or a timer. And that's why cooking outdoors is difficult. To make good food outdoors you need to become master of the flame and keeper of time. Many grills come with a thermometer, but they are usually crap. The thermometer on my gas grill is often off by 100°F! You absolutely positively must have a good oven thermometer. In addition to knowing what temp your cooker is, you need to know what temperature your meat is. Cooking without a meat thermometer is like driving without a speedometer. You might think you're under the limit, but try explaining that to the judge. You might think the meat is ready, but try explaining that to your guests when it is dry enough that they ask for a glass of saliva to help them swallow. Here is a meat temperature guide, and here's everything you need to know about thermometers with links to good ones you can buy. Some of the better digital thermometers have timers. If yours does not, get in the habit of wearing a watch when you cook and write down what time you put the meat into the heat in a cooking log. Some of the old timey barbecue artisans say you can learn to cook by sight, smell, and feel. That's just plain BS. Once you know how to cook you can rely more and more on your senses, but until you are ready to call yourself a top chef, get a thermometer, wear a watch, and keep a log like I do. The temperature of your food moves slowly upward during cooking, but the thickness of the meat is a major factor in how long it takes to cook. A thin steak cooks faster than a thick steak. So any recipe that says "cook your steak for 3 minutes per side" without specifying the thickness of the steak, is seriously flawed. Beware.

The Maillard reaction and caramelization As the surface of foods heat above 310°F, amino acids and sugars react together, scores of new compounds form, and the surfaces start to brown, a process called the Maillard reaction, and it develops a richness and depth of flavor, not to mention crunchy texture. Steaks get grill marks, roasts develop a bark, loaves of bread form crusts, slices of bread turn golden in the toaster, coffee beans turn dark when roasted, and fried potatoes darken. The sugars also begin to caramelize, contributing to the complexity.

The moisture thing As moisture evaporates, meat begins to shrink. A slab of pork ribs can lose 20% or more of its weight in cooking due to shrinkage. So we are faced with a problem. To liquefy the collagens so plentiful in ribs, we need to cook them to about 180°F. But by then it is well past well-done and the muscle fibers are drying out. So we try to add moisture. Water pans. I'm a big fan of putting a water pan above the coals or below the meat or both. Water pans pump moisture into the atmosphere of the cooker and that helps slow evaporation from the surface of the meat. Some of the moisture will even condense on the meat, which is cooler than the air, thereby basting it. Water pans can also help develop flavor and the smoke ring by mixing with the combustion gases and penetrating the meat surface. Some folks like to put wine or fruit juice in the pans. I think this is a waste of money. Steaming. Another method of adding moisture is to cook the meat in very high humidity by wrapping it in foil with a little water or juice for part of the cook. This keeps moisture from escaping and some vapors penetrate the meat. This method is called the Texas Crutch. A lot of competition cooks use the Texas Crutch on their ribs, pork shoulders, and brisket. At home, I always wrap brisket, but rarely bother to wrap the others. Injecting. Another method is to pump up the meat with moisture prior to cooking. You could use a hypodermic with flavorful marinade, and that is a great idea for thick cuts like pork shoulder and beef brisket, but it's not very practical to inject between each rib. A bit tedious, and the result doesn't taste like pork. Marinating. You can marinate meat. Marinating works well on leaner and more porous meats like chicken, but the fact is that most marinades do not get very far beyond the surface. You could marinate for several days, but that will also pull out much of the pork flavor. Brining. Brining adds a significant amount of moisture, it helps retain moisture during cooking, contributes noticeable flavor enhancements, and it's relatively quick: One hour for ribs. Max. It works great, but most of the time I just don't bother. For more on the subject, click here. Mopping, basting, spritzing. A popular method is to mop, baste, or spritz the meat frequently with flavored water, oil, beer, marinade, vinegar, or fruit juices while cooking. This helps cool the exterior but muscle fiber and fat do not absorb a lot of liquid, especially when they are partially cooked. Flavor comes when the liquids dry and leave behind flavor compounds. Saucing. Another method to get moist meat is to serve it with a sauce. But you knew that. This site has recipes for all the important regional barbecue sauces with which you can experiment. Just click here. Thin sauces penetrate the meat more easily than thick sauces and bring more moisture to the party.

Boiling temps Another important concept to know is that when a liquid is heated, its temp will increase until it hits its boiling temp and not go any higher. So no matter how much heat you put under a pot of water, the water will not get hotter than 212°F. If you have a sauce made of wine and olive oil it will heat to the boiling temp of alcohol, about 79°F, and hold there until all the alcohol is boiled off, and then rise to the boiling temp of water (wine is mostly water), 212°F, until all the water boils off, and then rise to the boiling temp of the oil, about 572°F.

The Thermodynamics of Cooking and How Different Cooking Methods Work

The different cooking methods

A brief discussion of cooking methods and terminology is worthwhile. Often these methods are combined. For example, beer can chicken, where a chicken sits on an open can of beer combines steaming in the cavity and roasting on the outside. For more definitions of cooking and barbecue terminology, check out this glossary.

Baking. Cooking with dry heat in an enclosed vessel such as an oven or in a large lidded pot. See also, roasting.

Barbecue (also: Barbeque, BBQ, Bar-B-Q, Bar-B-Que, Bar-B-Cue, 'Cue, 'Que, Barbie). There are at least nine spellings and a dozen or so definitions. I had to devote a whole page to the Definition of Barbecue.

Blanching. Foods are submerged in boiling water for a very short time, usually less than five minutes, and then they are usually moved to cold water. The process is used to partially cook a food, to loosen skins on nuts to make them easy to remove, to make green vegetables, especially string beans, bright green,

Boiling. Cooking by submerging in water that has large bubbles. Those bubbles are steam rising to the surface. Water boils at 212°F (100°C) at sea level and once it hits that temp it does not rise any higher, no matter how much heat is applied. Alcohol boils at 172°F. Boiling temperatures decrease as you go up in altitude because the column of air on top of the liquid is shorter and exerting less pressure so it is easier for water vapor, in the form of steam, to escape. The boiling temp of water is about 203°F in Denver. If you are cooking with wine, a mixture of about 12 to 20% alcohol, the alcohol will boil first and the temp will hold somewhere just higher than 172°F until the alcohol is mostly gone, and then it will rise to 212°F and hold there until the water is mostly gone. You cannot make liquids boil faster by increasing the heat. Boiling is a very severe method of cooking and can easily damage food by breaking down its structure and squeezing out its moisture. That's right, boiled food can be dry. And tough.

Braising. A wet method of cooking similar to stewing, poaching, or simmering, but the food is usually not submerged as they are in those methods. It is only partially covered in hot, but not boiling liquid for a long time, perhaps 6 to 12 hours. Braising is usually done in large pots like Dutch ovens or slow cookers and the lid is usually not on tight. This keeps the food in the air cooler than the 212°F of the liquid, and allows it to tenderize without drying out as easily. The result is a moist meal where everything in the pot gives up its goodness in the name of the whole, and like an orchestral symphony, no single instrument stands out.

Broasting. A trademarked method of deep frying in a pressure cooker.

Broiling. Direct heat cooking with flame. Similar to grilling. In recent years the meaning has been confused, and many people refer to broiling as when the flame is directly above the food, but technically it can be either above or below.

Char broiling. Broiling over charcoal although the large grill manufacturer Char-Broil makes far more gas grills than charcoal grills.

Curing. Although heat is not necessary to cure meats, and in fact curing is usually done at cool temps, it is like cooking in that it changes meat chemistry. Curing involves the preservation of meat by the heavy application of some or all of the following: Salts, sugars, nitrates, nitrites, or smoke. Each works differently by altering meats chemistry, inhibiting some microbial growth and promoting others, altering enzymatic digestion, changing the color, and of course, flavoring the meat.

Deep frying. Cooking at high temperature, usually 350 to 360°F, by submerging in oil or fat. This method creates more heat than boiling. The high heat creates steam within the food which cooks it and creates pressure at the interface between the food and oil preventing the oil from penetrating if the temperature is properly set. Deep fried foods are usually crisp on the exterior and moist in the interior. Because deep fried foods are often dipped in starch or batter, they can be extra crispy. This batter can absorb significant oil, however.

Drying. The process of dehydrating food by warming it slightly in a low humidity, high airflow environment. An excellent method of food preservation since most microbes need water to thrive.

Freeze drying is done by freezing the food in a low pressure environment, and then a small amount of heat is applied to sublimate the moisture.

Grilling. Cooking with direct heat over flame or directly over a heat source. Grilling is usually hot and fast cooking.

Microwave Cooking. This is a clever and fast method of cooking by exciting the molecules deep inside the food until they vibrate and heat without heating the air around it. The effect is similar to steaming. There is no dry heat to create the Maillard effect.

Pan Roasting. The chef starts a piece of meat, often a thick piece of fish, by browning and crisping the exterior in a thin layer of hot oil in a frying pan. But the meat is still uncooked in the center, so she puts the pan in the oven to finish cooking. The result is fried on the top and bottom, and baked in the center.

Planking. This is a combination method of indirect cooking especially popular with salmon. A wood plank, usually untreated western red cedar, which is porous and aromatic, is soaked in water. The food is placed on top of the plank and the plank is placed over direct heat in a closed oven. The plank heats the food by conduction, the water creates steam, the underside of the plank burns creating smoke, and the food roasts in the closed environment. That's conduction, steaming, smoking and roasting. Alder is also a popular wood for planking. Cooking planks are usually labeled as such. It is important that you do not use construction woods for planking because they can be treated with poisonous preservatives.

Poaching. Similar to stewing, but poaching is usually done in water, or water with just a little salt and/or vinegar added.

Pressure Cooking. Pressure cookers are heavy sealed pots with a locking lid and a high pressure release valve. A small amount of moisture is placed with the food in the cooker. As the pot heats up, moisture and pressure build. The boiling point of water rises as pressure builds, so the food cooks at a higher temp and thus faster than when steaming under normal pressure. The product resembles braised or simmered food.

Roasting. Originally this was a method of cooking in the open in front of an open flame. Today it often refers to cooking in an enclosed oven with medium to high heat, i.e. baking. Originally the food was exposed to heat only on one side at a time, now the food is usually surrounded by dry heat and it browns with the Maillard effect and caramelizes. Food can be roasted on a grate, in a pan, on a spit, or other carrier.

Rotisserie. A form or roasting where the food rotates in front of or above a flame so that the meat gets hot on one side and then cools and gets hot again, etc. Some of the heat is absorbed into the food and some dissipates in the air. The interior cooks evenly.

Sautéing. This is a method of cooking food in a small amount of fat over a high heat on a hot metal surface, usually in a frying pan or skillet, with the goal of rapid cooking and browning. This method helps the food retain moisture and helps prevent it from absorbing oil. To be successful it is important the food is not too cold, the surface of the food must be dry, and the pan cannot be crowded. Sautéing onions and garlic reduces their bite and pungence, and converts some of the compounds to sugar giving them a sweetness.

Simmering. See stewing.

Smoking. Smoking is a way to cook, flavor, or preserve food by exposing it to smoke, usually from wood, although other combustibles, usually cellulosic, such as corncobs, tea, and herbs are used. At one time, before refrigeration, smoking was a widely used method of preservation. But it is not good for all foods since smoke does not penetrate very far.

• Cold smoking is usually done at temperatures under 125°F. The food is heavily infused with smoke flavor, but it is not cooked by heat. This method is tricky because the temperature is ideal for growth of microbes, and, although smoke has preservative properties, unless done properly cold smoking can produce food that is dangerous. For this reason cold smoked meats are often heavily salted, brined, or otherwise cured. Cold smoking of meats should be left to professionals. Most commercial smoked fishes and cheeses are cold smoked.
• Hot smoking is usually done at temperatures in the 165 to 200°F range. These foods are often also brined or otherwise cured. Most American smoked hams are hot smoked.
• Smoke roasting is usually done in the vicinity of 200 to 250°F. The food is cooked by the heat, and when it is finished it is free of harmful living microbes. At these temperatures not much shrinkage occurs. Smoke roasting is relatively easy to do on backyard smokers and barbecue equipment. Most of the best barbecued ribs, pulled pork, and briskets in this temperature range.

Sous-vide. Sous-vide is French for "under vacuum" and it means putting the meat in a vacuum sealed plastic bag and immersing it in water at the temperature at which you plan to serve it for hours, even days! It is similar to poaching but more flexible. The process also prevents liquids from escaping, and some chefs add butter or sauce to the bag to build more flavor. Meats come out uniform in color and texture throughout, so they are sometimes seared after cooking to create a Maillard effect crust. The results can be spectacular. Sous-vide must be done correctly because if you do it wrong, you die of botulism. In October 2009 SousVide Supreme was introduced for home use at $399.

Steaming. The food is placed in an enclosed container above boiling water. Steam penetrates the food. It is a very effective method of tenderizing and moisturizing and it is fast.

Stewing. Food is cooked under a water based liquid at temperatures that create only a few small bubbles usually between 160 to 211°F. Stewing usually is a slow cooking process. Stewed meats are usually browned by sauteing or broiling first to add flavor. These methods can be done in a pot over a heat source or in a slow cooker. The liquids are usually flavored with stock, wine, vegetables, herbs, etc.

Stir frying. Similar to sautéing, but the food is cooked in a curved pan called a wok, and the food is often not browned.

Surface frying. This is frying in a thin layer of oil on a hot metal surface, much like sautéing, but usually on a griddle. Only one surface at a time fries as opposed to deep frying. Diner burgers are a great example.

Sweating. Like sautéing, but at much lower temperatures. Food is placed in a pot or pan with enough fat or oil to coat it but cooked at low temperatures until it softens or wilts.

This page was revised 4/22/2010