Every time I open the refrigerator door, Alex, my Siamese cat, eyes the contents like Willie Sutton peeking into Fort Knox. He knows that that big, white impregnable strongbox contains all the pleasures life has to offer. (He's neutered.)
We humans aren't much different. Our refrigerators are our treasure houses. Their contents reflect our individual lifestyles even more than the clothes we wear or the cars we drive. There are even Web sites on which certain self-absorbed individuals post the contents of their refrigerators as a sort of poor-man's autobiography. ("Olives stuffed with garlic, six; Hershey's chocolate syrup, one-eighth can; pomegranate, rotten: one.")
The main purpose of a refrigerator, of course, is to exhibit every silly object that can conceivably be glued to a magnet. But in addition, refrigerators produce low temperatures, and low temperatures slow down everything--from chemical enzyme reactions that spoil food to living food spoilers such as bacteria, yeasts and molds.
There are two kinds of bacteria we want to inhibit: pathogenic (illness-causing) bacteria and spoilage bacteria. Spoilage bacteria make food repulsive and inedible, but they generally won't make you sick. Pathogenic bacteria, on the other hand, may be completely undetectable by taste or appearance, but are still dangerous.
And now, Alice, would you like to take a tour of Refrigerator Wonderland? Just drink this bottle labeled "Drink Me" to make you small, and follow the white rabbit into the fridge.
Alice: Brrr. It's freezing in here!
White Rabbit: We've landed in the freezing compartment at the top of the fridge. It's the coldest part, and it's usually at the top because any cold air leakage will fall down and help cool the lower parts.
A: Just how cold is it in here?
WR: A freezing compartment should always be at zero degrees Fahrenheit or colder. That's 32 degrees below water's freezing temperature.
A: How can I tell if my freezer at home is cold enough?
WR: Buy a refrigerator-freezer thermometer, which is specially designed to be accurate at low temperatures. Nestle it among the frozen food packages in your freezer, close the door and wait six to eight hours. If the thermometer doesn't read within a couple of degrees of zero, adjust the refrigerator's control knob and check again six to eight hours later.
Now let's climb down into the main part of the fridge, where it's quite a bit warmer.
A: You call this warm?
WR: Everything's relative. Outside in the kitchen it's at least 30 degrees warmer. The refrigerator is removing heat from the box we're in, but heat is energy, and you can't just destroy energy; remove it from one place and it has to go someplace else. So the refrigerator throws it out into the kitchen. The Mad Hatter claims that a refrigerator is really a kitchen heater, and he's right. In fact, a refrigerator puts out more heat than it removes from its interior. That's why you can't cool off the kitchen by leaving the refrigerator door open; you'd just be moving heat around from one place to another, not getting rid of it.
A: How does the refrigerator remove heat?
WR: It contains an easily vaporizable liquid called Freon, or at least it did before scientists discovered that Freon destroys Earth's ozone layer; new refrigerators contain a friendlier chemical with the jabberwocky name of HFC134a. Anyway, when a liquid vaporizes (boils), it absorbs heat from its surroundings, which get colder (no room in here to explain why), and when the vapor is compressed back into a liquid, it releases that heat back out again. A refrigerator allows the liquid to vaporize and cool those metal coils you see on the wall. Then it compresses the vapor to a liquid again (that humming you hear is the compressor motor), but it dissipates the resulting heat through a maze of outside coils hidden behind or beneath the box. A thermostat turns the compressor on and off as needed to maintain the proper temperature.
A: What is considered proper for a temperature?
WR: The main compartment of a refrigerator should always be below 40 degrees Fahrenheit. Above that temperature, bacteria can multiply fast enough to be dangerous.
A: Can I use my new thermometer to measure that?
WR: Absolutely. Put it in a glass of water in the middle of your fridge and wait six to eight hours. If it doesn't read 40 degrees or below, adjust the thermostat's control knob and check the temperature again six to eight hours later.
A: I'm certain that any refrigerator of mine will prove to be at precisely the proper temperature, thank you. But whatever shall I keep in it?
WR: You know, the usual stuff. Live crabs--it sedates them so they don't throw off their claws when you steam them; table cloths with candle wax on them--you can scrape it off after it gets hard; damp laundry in a plastic bag whenever you can't iron it right away.
A: All right, smarty. Is there anything that should not be kept in the refrigerator?
WR: Yes. Tomatoes lose flavor when chilled below about 50 degrees because an important flavor chemical dissipates. Potatoes get unpleasantly sweet because their starch turns to sugar. Bread dries out and gets stale if not tightly wrapped, yet it can get moldy if put into a plastic bag. Better to freeze it. And a large amount of leftover food that is still warm can raise the fridge's temperature to a dangerous, bacteria-friendly level. Divide it up into small, easily cooled containers and chill them in cold water before putting them in. Don't let them cool on the counter, because they'll be at a dangerous temperature too long.
A: I once heard a song about never keeping bananas in the refrigerator, cha cha cha.
WR: Chiquita has changed her tune. It's okay now. Let your bananas ripen at room temperature to the stage you prefer (green-tinged, all yellow or flecked with brown) and then put them in the fridge to stop the ripening process. But the skin will turn black from enzyme reactions.
Alice, watch out! You're too close to the edge of the shelf!
A: Help! I've fallen down into this drawer. Where am I?
WR: You're in the crisper.
A: I don't think I want to be crisp.
WR: It's only for fruits and vegetables, and it controls humidity rather than temperature. Vegetables will dry out and get flabby unless the humidity is kept relatively high. The crisper is a closed box that keeps water vapor in. But fruits require a lower humidity than vegetables, so some crispers have adjustable openings that you're supposed to readjust every time you change the contents.
A: Yeah, sure. Now what's that other compartment below us?
WR: That's the meat keeper. Meats have to be kept as cold as possible. The meat keeper is at the bottom of the fridge because cold air sinks. And speaking of meats, I'm late for a very important "meating." Here. Drink this other bottle of "Drink Me" to make you big again and we'll get out of here.
Don't forget to turn out the light.
Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh and the author of "What Einstein Didn't Know--Scientific Answers to Everyday Questions." Send your food or cooking questions to email@example.com.