I'm Just Here for the Food_ Version 2.0 - Alton Brown [5]
DEFINITIONS
Degrees (either Fahrenheit or Celsius) are units of heat measurement—not heat units. In the kitchen, the heat units we need to be concerned with are BTUs and calories.
A BTU (British thermal unit) is the amount of heat energy required to increase the temperature of a pound (pint) of water by 1° F.
A calorie is the amount of heat needed to raise the temperature of 1 gram of water from 58° to 60° F. Although any heat-producing device, from a refrigerator to a nuclear power plant, can be rated in calories, the term is usually used to describe the potential heat energy of food. So the next time you feel bad about noshing on that 378-calorie candy bar, rest easy in the knowledge that your body can, through various chemical reactions, produce enough heat to warm 13.3356 ounces of 58° F water by 2° F.
Physical reaction. Fire is a physical reaction wherein a fuel (oxygen) combusts in the presence of a catalyst (a chunk of charcoal).
When it comes to getting heat to food, there are really only two methods of transferal: radiation and conduction. Radiation works on food via waves, conduction is a little trickier.
Basically, conduction is what happens when a piece of matter that’s hot comes into direct contact with another piece of matter that isn’t. Since heat always moves toward areas of lesser heat, the hot matter makes the less-hot matter hotter. The transferal matter in question can be anything from air to a chunk of metal. However, different types of matter react differently when hot. Metal atoms, locked in a crystalline structure, can only vibrate and pass the energy along—like those funny contraptions you see in executive offices with the series of suspended metal balls; when you lift one and let it fall, the one on the far end swings up. The atoms that make up water and air are different: they’re fluid and can move about freely—and this changes everything. Left to their own devices, hot gases and liquid molecules will expand and (becoming less dense) rise. As they give up their heat to other bodies, they cool and sink, thus setting up a natural convection current. Whether in an oven, a pot of water, or a desert, the effect is the same.
The faster the convection current, the more hot matter comes in contact with the item to be heated—in our case, food. This means that a blast of 150° F air can cook something faster than a 500° F oven. Don’t believe it? Try this experiment:
Buy an ice cream cone on the hottest day of the year and eat it in your car in the parking lot with the windows up (no air conditioning please). The cone will indeed melt, but unless you’re in Death Valley it won’t happen so quickly that you can’t keep up with it. Now, buy an identical cone on a cold day and eat it while driving with the windows down. The cone will melt much faster—so fast in fact that you probably won’t be able to stay ahead of it. Even though the air is much cooler, more of it is coming into contact with the cone, so there is more transference of heat.
What we can take from this is that although the heat is still moving via conduction, the convection rate is actually an equal if not greater consideration. This is why convection is usually considered as its own classification of heat transference. Here it is in slightly different terms.
Let’s say it’s an average Wednesday night in the early Stone Age and you, an average Homo erectus, return to your cave with a nice big mammoth steak. You could chew it up raw, or you could:
a. Build a fire and hang the hunk a foot or so over the flames. This would be cooking via convection. That means that the vapor (smoke) and the surrounding air will absorb the fire’s heat, expand, and rise upward. Since hot always moves to cold, part of this thermal energy moves into the