What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (44 page)
Read What Einstein Kept Under His Hat: Secrets of Science in the Kitchen Online
Authors: Robert L. Wolke
| | Smoky Garlic Mayonnaise | |
S
moked Spanish paprika,
pimentón
, adds a subtle hint of wood fire to this garlic mayonnaise. It is a classic accompaniment to paella (p. 258), and is also good with Hot-Wok Mussels (p. 255). You can use it as a dip for raw vegetables, or serve it with steamed fish, especially with fresh cod. If the flavor is too intense, half olive oil and half peanut oil makes a delicious dressing.
For herb mayonnaise, add
1
/
2
cup minced fresh herbs (parsley, chives, chervil, tarragon) in place of the garlic in step 2. A blender does the best job of blending the herbs into the emulsion.
1 large egg
1 teaspoon smoked Spanish paprika (
pimentón
)
1
/
2
teaspoon dry mustard
1
/
2
teaspoon salt
2 tablespoons cider, sherry, or wine vinegar
1 cup mild extra-virgin olive oil
1 large clove garlic, coarsely chopped
1.
Break the egg into the blender container. Add the
pimentón
, mustard, salt, and vinegar. Add
1
/
4
cup of the oil. Cover the container and turn the motor on to low speed.
2.
Immediately uncover and pour in the remaining oil in a fine, steady stream. Do not hurry. When all the oil has been incorporated, add the garlic (or the herbs, if using). Continue to blend for 1 minute, or until smooth.
3.
Allow the mayonnaise to rest in the refrigerator for at least 1 hour before using, so the flavors will mellow and soften. Refrigerate for up to 4 days. Don’t serve it cold, because chilling dulls the olive oil flavor.
MAKES ABOUT 1
1
/
4
CUPS
| | HOME ON THE RANGE | |
Oven temperatures are pretty easy to control; the dials have actual temperature numbers on them. But what about stovetops? I have a gas cooktop, and the controls are marked “hi,” “med,” and “lo.” Two of them burn at higher Btu’s than the other two; “med” on them is hotter than “hi” on the other two. I used to have an electric cooktop with the same markings, but their cooking speeds were completely different from my gas range. Are there any industry standards for burner temperatures?
....
U
nfortunately not. The only standard that I know of seems to be that
high
is spelled “hi” and
low
is spelled “lo.” In between “hi” and “lo,” my gas range has the digits 2 through 9, but the numbers indicate nothing whatsoever about temperature. The labels “hi” and “lo” and the numbers 2 to 9 refer not to the temperature but the rate at which the burner is generating heat.
There is a lot of confusion about the words
heat
and
temperature
in the food world, so maybe it’s “hi time” for me to give you the “lodown.”
First of all, heat and temperature are two different things. Heat is a form of energy, distinct from gravitational energy, electrical energy, energy of motion (
kinetic
energy), or nuclear energy. It is, in fact, the ultimate form of energy into which all other forms eventually degenerate. (See “The energy tax,” p. 389.)
Cooking employs heat to cause physical and chemical changes that we hope will improve the food’s tenderness, digestibility, and flavor. It should come as no surprise that when a food (or anything else) absorbs heat, it gets “hotter,” meaning that its temperature rises. But what is temperature? It’s nothing more than a convenient number invented by humans (Mssrs. Fahrenheit and Celsius; see “Untangling F & C,” p. 388) to indicate how much heat energy a substance contains. In cooking, specific changes take place when a food reaches specific temperatures, that is, when the food acquires enough heat relative to its size. You might say that temperature measures the concentration of heat in a substance.
So it’s the temperature of the food, not the temperature of the gas flame or electric burner beneath the pot or pan, that matters to the cook. The burner is there only to pump heat into the food, no matter what its own temperature may be while doing it. We could place a white-hot poker beneath a frying pan, but it would be a terribly inefficient way to heat the food in the pan.
Then why do we say that one burner at a given setting is “hotter” than another? It’s just loose talk; we don’t really mean to imply that its temperature is higher. We mean only that that burner pumps out heat at a faster rate than the other one, thereby raising the food’s temperature—and cooking it—faster. Instead of “hi” and “lo,” then, we should really label the burner settings “fast” and “slow” (or, inevitably, “slo”).
Different burners, whether gas or electric, do indeed pump out heat at different rates. We measure those rates in Btu’s per hour. A
Btu
, or
British thermal unit
, is an amount of heat energy, just as a calorie is. (A nutritional calorie happens to be almost exactly equal to four Btu’s.) But what’s important about a cooktop burner is how many Btu’s or calories it can pump out
per minute or per hour
. The number of Btu’s pumped out per hour is a good indication of how fast a burner will heat and cook our food. A candle, for example, gives off a total of about 5,000 Btu’s of heat over a period of a few hours, but that’s hardly fast enough to cook with, because its Btu-per-hour rate is pathetic.
Most people, including appliance salesmen and cookbook authors, either are too lazy to say “Btu’s per hour” or don’t know the difference, so they (as you did in your question) speak simply of “Btu’s” as if they were a measure of heating speed. But as Tony Soprano would say, wha’y’gon’do?
A home gas or electric range burner may put out between 9,000 and 15,000 Btu’s per hour at their maximum settings. Check the literature that came with your range or contact its manufacturer to find out the ratings of your burners, and you’ll know which ones are hotter (whoops! I mean faster).
In cooking, what ultimately counts is how fast the temperature of the food rises to its optimum cooking temperature and how steadily it will remain there at different burner settings. But alas, the burner’s setting can be only a rough guide, because no matter what its Btu-per-hour rating, most of the heat it generates goes into heating up the kitchen.
Experience with a given cooktop will teach you approximately what each combination of burner and setting can accomplish. But good cooks simply keep an eye on what the food itself is doing, continually judging whether more or less heat is called for and adjusting the burner accordingly.
Life is tough.
Untangling F & C
In 1714 a German glassblower and amateur physicist named Gabriel Fahrenheit (1686–1736) made a gadget that would indicate how hot or cold an object was by how far up or down a thin column of mercury inside a glass tube would expand or contract as its temperature changed. To put numbers on it, he decided that there should be 180 “degrees” between the freezing point and the boiling point of water. Then he made up a batch of the coldest concoction he could create—a mixture of ice and ammonium chloride—and called its temperature zero. When he stuck his gadget into freezing water, the mercury went up 32 degrees higher than that. Since boiling water was to be 180 degrees higher than
that
, it came out to be 212. And that’s how we got those crazy numbers, 32 and 212.
Six years after Fahrenheit himself cooled to room temperature, a Swedish astronomer named Anders Celsius (1701–1744) decided that it would be more convenient if there were only 100 “degrees” between the freezing and boiling points of water. So he set the freezing point at zero and the boiling point at 100. And that’s how we got the Celsius scale of temperatures.
Every chance I get, I lobby for a little-known, simple method of conversion between Fahrenheit and Celsius temperatures. (And yes, it’s in all my other books, and I’ll keep doing it until everybody gets it right!) Forget those confusing formulas you learned in school. (Do you add—or is it subtract—32 before—or is it after—multiplying—or is it dividing—by 5/9? Or is it 9/5?)
My way is as easy as 1-2-3:
(1) Add 40 to the number you want to convert (either F or C).
(2) Multiply or divide the result by 1.8.
(3) Subtract 40.
That’s it. All you have to remember is the fact that Fahrenheit temperatures are always bigger numbers than their Celsius equivalents, so you
multiply
by 1.8 to convert from C to F, and you
divide
by 1.8 to convert from F to C.
Example: 212°F + 40 = 252
252
÷
1.8 = 140
140 – 40 = 100°C
. . . and that’s just what you expected it to be, right?
Sidebar Science:
The energy tax
HEAT, THE
energy we use in cooking, is the most universal form of energy. All other energy forms—chemical energy, energy of motion (
kinetic
energy
), electrical energy, nuclear energy—eventually degenerate into heat, which you might say is a sort of energy of last resort. As chemical reactions give off energy, as moving things slow down, as a lamp converts electrical energy into light, as uranium atoms convert mass into radioactivity and heat, there can never be a 100 percent conversion. Inefficiency seems to be built into the universe. Some of the lost or converted energy must inevitably be “wasted” by being turned into heat. You might think of heat as a tax on the conversion of energy; it’s like the fee charged by a money exchanger for converting one form of currency into another.
Most forms of energy can be well-behaved. For example, kinetic energy is well-behaved when a truck is moving in a straight line down a highway. Electrical energy is well-behaved when the movement of electrons is being controlled by a circuit. Nuclear energy comes from the
very
carefully controlled splitting of atoms. In contrast to all this, however, heat is a shockingly ill-behaved and disorderly form of energy, because it consists of the wild, random movement of atoms and molecules.
The science of
thermodynamics
has found that whenever a form of energy, such as the chemical energy in a truck’s diesel fuel or in the uranium of a nuclear reactor, is being converted into another form, the disorderliness or randomness (the
entropy
) of the system must increase. That’s the Second Law of Thermodynamics. The universe is inexorably winding down by losing energy and creating disorder. Chaos.
So whenever a form of energy is being used up or converted into another, some of a disorderly, more chaotic, higher-entropy form of energy must be produced. That’s heat.
For further details, consult your friendly neighborhood thermodynamicist.
| | FOILING BROILING | |
I’ve been trying to get some answers to questions about oven broilers. They seem to be the most inconsistent of all kitchen equipment. I’ve moved several times and have had several broilers. One may sear a steak beautifully, while another steams it before it can get brown. How far from the heat should the food be? What about gas versus electric? Preheat or not? Door open or closed?
....
Y
ou’re right to be befuddled. Of the six basic methods of cooking, broiling is the hardest to control.
What are the six basic methods, you ask? They are (1) immersion in hot water or stock (boiling, poaching, stewing); (2) exposure to hot water vapor (steaming); (3) immersion in hot oil (deep-frying); (4) contact with hot metal (pan-frying, sautéing, searing, grilling); (5) exposure to hot air (baking, oven roasting); and (6) exposure to infrared radiation. That last-named method is what we call broiling. (Okay, add the absorption of microwaves to the list if you wish.)
Maybe you think you don’t broil with infrared radiation. But the molecules of anything that’s hot, such as the flame or heating element in a broiler, are emitting infrared radiation, a kind of electromagnetic energy that other molecules can absorb with the result that they become hot in turn. You can feel the warming of the molecules in your face when you walk by anything that’s hot, such as a red-hot furnace or even a range burner that you forgot to turn off. So any cooking method that involves a source of heat—and what method doesn’t? (okay, except microwaves)—is cooking the food at least partially by shooting infrared radiation at it.
Broiling cooks food almost entirely by infrared radiation. The heat source, whether a red-hot electric element or a line of gas flames, doesn’t touch the food; it bathes it in intense infrared radiation, which is absorbed by the top surface of the food, heating it to 600 to 700°F (320 to 370°C) and searing and browning it quickly. Then, after you turn the food over, the same thing happens on the other side.
In electric ovens set on “broil,” only the top heating element gets hot, and the food is placed close beneath it. In some gas ovens, the burner may be beneath the oven floor, doing double duty by also heating the oven, so the food to be broiled must be placed even below that, usually in a drawer-like arrangement.
But we all learned in school that heat rises, didn’t we? So how come we can cook food
beneath
the source of heat? Well, pardon me, but heat doesn’t rise. Heat from a hot object can flow up, down, or sideways. It will flow into any cooler object with which it happens to be in contact. What people mean when they say heat rises is that
hot air
rises. Heated air expands and becomes less dense, so it floats upward through the denser, cooler air like a bubble in water.
