ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Wednesday, November 13, 1996 TAG: 9611130029
SECTION: EXTRA PAGE: 8 EDITION: METRO
SOURCE: PAT DAILEY CHICAGO TRIBUNE
Searing meat seals in juices.
Wrong.
Burying an avocado pit in a bowl of guacamole keeps the green dip from turning brown.
Wrong.
If you're making ice cubes, use the coldest water that flows from the tap; they'll freeze more quickly.
Wrong.
Wrong, wrong, wrong, fractured fiction all, says Harold McGee, the wizard of whys and why nots and author of ``On Food and Cooking: The Science and Lore of the Kitchen'' and ``The Curious Cook.''
If there's a kitchen myth that needs debunking or a lingering old tale that could use some rewriting, McGee's the man to do it. The culinarily curious McGee, 45, has wed the principles of science with the needs of the cook. In doing so, he has tackled some of the most commonly accepted myths that come out of the kitchen and, one by one, they fall like October leaves after a rainstorm.
Is McGee a food scientist by trade? Chemist, perhaps, or physicist? As it happens, no. A former teacher, he has a doctorate in English literature from Yale University. And for all the theories and experiments, test tubes, thermometers and scales that are the tools of his trade, he is no lab-locked egghead. He lives in Palo Alto, Calif., where he works at home.
McGee says curiosity is in his genes. (He traces it to his father, who used to make parsnip wine in the closet so he could taste a basic fermentation.)
To the chagrin of his wife, Sharon Long, a biologist, McGee is almost behaviorally unable to just cook a meal.
``I dissect everything, experiment, weigh it, analyze it. There are times my wife walks in, sees the green beans in a beaker and groans, `Can't we just eat the food?''' McGee said.
During a recent visit to the Chicago Tribune, McGee turned the test kitchen into a little lab, demonstrating some of the ways science is put into action at dinner time.
Searing science
``Searing meat seals in the juices,'' one of the best-known of all cooking directives, was first proclaimed in the 19th century by a German scientist. So it must be right, right? Justus von Liebig insisted that high temperatures coagulated proteins on the surface, making it nearly impossible for juices to seep through the crusty exterior and be forever lost. Had he bothered to apply scientific inquiry to the theory, he would have discovered that quite the opposite was true - the meat actually loses more juice than when it's cooked at a very low, steady temperature.
McGee offers a simple experiment: Pat a steak dry and place it in a hot skillet over high heat. Sear the bottom, giving it a nice crusty finish. Flip it over to cook the other side and watch closely. It steams and sputters, both signs that moisture has left the steak to become part of the atmosphere. And almost instantly, the seared top will begin to ooze with mouthwatering juice, much of which will evaporate as the steak cooks.
``Juiciness also is a direct function of how well-done meat is cooked. A rare steak is always juicier, no matter how it is cooked,'' McGee said.
End of story? Not quite. He's quick to add that a seared steak tastes better because the surface caramelizes, intensifying the flavor.
Bottom line: Sear the meat for flavor, but don't overcook it.
Avocado brown
An avocado pit keeps guacamole from turning brown:
``Hippy, dippy magic,'' McGee said, dismissing that bit of lore. He has a bright idea to prove it. Bury an avocado pit in one bowl of guacamole and a small light bulb - same shape, same size - in another. An hour later, the top of each dip is an unappetizing shade of brown. Pluck out the pit and, indeed, the dip is delightfully green underneath. And beneath the light bulb? Also a field of green.
``There are no secret vibes or anti-browning agents in an avocado pit that keep it from turning,'' McGee said. ``It's just that it keeps that portion of the guacamole from being exposed to air.''
Oxidation is the culprit, but McGee said it can be stymied for a day or longer with the right wrap. Polyvinylidene chloride - Saran Wrap - is the least permeable of all brands of plastic wrap. Cover the guacamole completely, with the Saran Wrap placed directly on the surface, then smooth out all air bubbles. McGee said the guacamole will stay green for 24 hours. We tried it, storing it from Friday to Monday, and it still looked good enough to eat.
Lest you suspect that McGee is endorsing Saran Wrap, he added that there are some foods that are better off when wrapped in plastic that is more air-permeable.
``There are no perfect products,'' he said.
Running hot and cold
Common sense says cold water freezes more quickly than hot water. But even Aristotle knew it isn't necessarily so, noting that, ``When they want water to cool quickly, begin by putting it in the sun.'' In fact, boiling water can take as little as a third the time to freeze as room temperature water.
McGee said that in most experiments, the time difference isn't that dramatic. Usually, boiling water and tap water freeze in about the same amount of time. But he's quick to remind that boiling water has about 150 degrees further to go before freezing than tap water.
How can that be? McGee said the scientific principles behind this are evaporation and air currents. Hot water generates more steam than cold in the freezer - hence the evaporation creates a smaller mass to freeze. The steam also creates a microclimate above the water, its little jet streams cooling the water immediately beneath.
Volume control
French chefs have long held that a copper bowl is a must for beating egg whites, key to achieving the best volume and stability.
McGee said science backs them up on this one: Whites whipped in copper are creamier, more voluminous and harder to overbeat (which isn't very hard at all, as many cooks have unfortunately discovered).
Theories as to why this is true have included electrical fields set up by the copper and a favorable change in the egg whites' acidity. McGee nixed these notions and said copper provides stabilizing ions to the metal-binding protein in whites.
Ever practical, McGee said that in lieu of a costly copper bowl, adding cream of tartar to the egg whites has pretty much the same effect. Only a small amount is needed, about 1/16 teaspoon per egg white.
The yolk of the matter
You can't use raw egg yolks in recipes anymore because you risk contamination with salmonella bacteria. True? Not exactly. McGee has a method of near-boiling the yolks, cooking them just enough in a microwave oven to destroy salmonella but not so much that they coagulate. The directions must be followed exactly.
To make raw egg yolks safe to use, place two large egg yolks in a 2-cup glass measuring cup and beat them lightly with a fork or whisk. Beat in 2 teaspoons of lemon juice or vinegar. Add 2 tablespoons water and beat again. Put the fork or whisk in the sink and have a clean one ready (or wash the original one thoroughly to prevent cross-contamination). Cover the cup with a plate, place it in a microwave oven and heat on high power. Watch until the mixture begins to swell and become agitated. Start timing at this point and cook 8 to 10 seconds. Remove from the microwave oven and beat vigorously with a clean fork or whisk. Cover the cup, return it to the microwave, heat until it swells up and agitates again, then start timing and cook 8 to 10 seconds. Whisk again, with another clean fork or whisk, take the temperature of the yolks; it should be about 200 degrees F. Let stand one minute, then use in any recipe that calls for raw egg yolks.
More McGeeisms:
* Potatoes that are lightly oiled before baking will cook more quickly.
* Yes, it does help to blow on chicken soup to cool it off. But for pea soup, beef stew and other thick foods, it's less effective. Cool them, instead, by scooping up and stirring the contents.
* Although cooks swear by it, basting poultry doesn't add moisture to the bird because there's no way the basting liquid can penetrate the skin. But as the basting liquid evaporates on the hot food, it cools the surface, helping to prevent overcooking.
* Some custard sauce recipes suggest stirring with a wooden spoon. McGee says that advice is not as picky as it sounds. Metal spoons conduct heat more quickly - too quickly for a delicate, egg-based sauce.
* Olive oil is fine to use when making homemade mayonnaise, but don't use all extra-virgin olive oil. It contains a fat-related compound that interferes with emulsification, making it unstable. It looks fine until you dip in the first crudite and it breaks down. If you want the flavor of extra-virgin, use it for no more than a fourth of the oil in the recipe.
* Cooks wearing eyeglasses may have wondered about the oil that collects on the inside of the lenses. The oily rain rises above the glasses and showers over the inside of the lenses as the cook ponders the contents of the pot. McGee suggests wearing a billed cap.
* Did your mother warn you not to jump or walk too heavily when an angel food cake was in the oven, lest the lovely cake collapse? McGee said go right ahead and stomp to your heart's delight. But by all means, invert the cake as it cools or it will, indeed, fall to a new low.
LENGTH: Long : 159 lines ILLUSTRATION: PHOTO: KRT. Harold McGee calls himself a curious cook.by CNB