What Einstein Told His Cook (36 page)

Enter the pressure cooker. It boosts the boiling point of water up to 250ºF. How? I’m glad you asked, because the cookbooks rarely tell you, nor do the instructions that come with the cookers.

For water to boil, its molecules must gain enough energy to escape from the liquid and go flying off freely into the air as a vapor or gas. To do that, they have to push against the blanket of atmosphere that covers our entire planet. Air is light, but it goes up more than 100 miles and the blanket is therefore quite heavy; every square inch of it weighs about 15 pounds at sea level. Under ordinary conditions, water molecules must achieve energies equivalent to a 212ºF temperature before they are able to push through that 15-pound-per-square-inch (psi) blanket and boil away.

Now let’s heat a small amount of water in a pressure cooker, a tightly sealed container with a small, controllable vent for releasing air and steam. As the water begins to boil, it generates steam and, with the vent closed, the pressure inside the container builds up. Only after it has reached a total pressure of 30 psi—15 from the atmosphere plus an extra 15 from the steam—does the vent controller allow the excess steam to discharge into the kitchen. Thereafter, it maintains the pressure at that 30 psi level.

To push through this higher “blanket” pressure and keep on boiling, the water molecules must now achieve a higher energy than before. To overcome 30 psi of pressure, they require an energy equivalent to 250ºF, and that becomes the new boiling temperature. The high-temperature, high-pressure steam speeds cooking by permeating all parts of the food.

As you start to heat the sealed pressure cooker, the vent releases air until the water begins to boil and steam forms. The steam pressure is held at the desired 30-psi level by some kind of pressure-limiting device. In many cases it’s a little weight on top of the vent tube. During cooking, the weight wobbles aside to release all higher-than-30-psi steam, which hisses as it escapes and scares people into thinking the thing is about to explode. It’s not. Newer pressure cooker designs use a spring valve instead of a weight to maintain the pressure at the desired level.

During cooking, you adjust the burner so that the contents boil fast enough to maintain the steam pressure, but not so fast that an excessive amount of steam is lost through the vent. In any event, the pressure regulator won’t let you turn it into a bomb. After the allotted cooking time, you cool the pot down, so that the steam inside condenses—returns to liquid—and relieves the pressure. A safety device assures you that the pressure is gone (some models won’t even let you open them until then), whereupon you may open and serve.

KITCHEN MAGNETISM

My neighbors just remodeled their kitchen and installed an induction-heating cooktop. How does it work?

M
icrowave ovens were the first new way of making heat for cooking in more than a million years. Well, now there’s a second one: magnetic induction heating.

Magnetic induction has been used for the past decade or so in some European and Japanese foodservice kitchens, and more recently in commercial American kitchens. They are now beginning to appear in the home.

Induction ranges differ from electric ranges in that electric cooktops generate heat by the
electrical
resistance of metal (the burner coils), while induction cooktops generate heat by the
magnetic
resistance of metal: the metal in the cooking vessel itself.

Here’s how it works.

Beneath that beautiful, smooth ceramic surface on your neighbor’s cooktop are several coils of wire like the coils of wire in a transformer. When one of the heating units is turned on, the house’s 60-cycle alternating (AC) electric current begins to flow through it. For reasons that we won’t go into (and that even Einstein couldn’t really explain to his complete satisfaction), whenever electricity flows through a coil of wire it makes that coil behave like a magnet, complete with North and South poles. In this case, because the AC current is reversing its direction 120 times per second, the magnet is reversing its polarity back and forth 120 times per second.

So far, there’s no evidence in the kitchen that anything at all is happening; we can’t see, feel, or hear magnetic fields. The cooktop is still cool.

Now place an iron frying pan on top of the coil. The alternating magnetic field magnetizes the iron, first in one direction and then the other, switching its polarity back and forth 120 times per second. But magnetized iron isn’t quite so easily persuaded to reverse its polarity, and it resists the vacillations to a significant degree. That causes much of the magnetic power to be wasted, and the wasted power shows up as heat in the iron. As a result, only the pan gets hot. There’s no flame or red-hot electric coil, and the kitchen stays cool.

Any magnetizable (Techspeak: ferromagnetic) metal will be heated by this magnetic induction process. Iron will, of course, whether enameled or not. Many, but not all, stainless steels will. But aluminum, copper, glass, and pottery won’t. To see whether a given utensil can be used on a magnetic induction cooktop, take one of those silly magnets off your refrigerator and see if it sticks to the bottom of the pan. If it does, the pan will work for induction cooking.

So in addition to the substantial cost of a magnetic induction cooktop, you can’t use those treasured and expensive copper pans. Did your neighbors think of that before springing for their impressive, high-tech cooker?

LET THERE BE…HEAT!

There’s a new kind of oven that supposedly cooks with light instead of heat. How does it work?

I
s this a fourth new way of making heat for cooking, after fire, microwaves, and induction ranges? No. The so-called light oven makes heat in pretty much the same way your electric range does: through the electrical resistance-heating of metal.

Light ovens have been in specialized commercial use since about 1993 but are now being produced for home use. A countertop or wall-mounted FlashBake oven manufactured by Quadlux Inc. has been available since December 1998, while General Electric Appliances’ built-in Advantium ovens have been available since October 1999 to builders and contractors for installation in new kitchens.

When I first heard about the light oven, my skeptic button was pushed hard. Some of the promotional statements sounded like pseudoscientific hype: They “harness the power of light.” They cook “with the speed of light” and “from the inside out.”

Light does indeed travel, appropriately enough, at the speed of light, but it doesn’t penetrate most solids very far. Try reading this page through a steak. How, then, can light deposit enough energy inside the food to cook it, unless it is incredibly intense? I thought of lasers, those ultrapowerful beams of light that we use for everything from eye surgery to annoying the neighbors with little red dots, but their light is so compact and concentrated that at most they could zap one grain of rice at a time.

Ah, but there is “light,” and then again there is “light.” The secret of the light oven lies not only in the intensity of its radiations but in the blend of wavelengths that it generates. Here’s how it works, based on information I gathered from some of GE’s techies. (They wouldn’t divulge
all
their secrets.)

“AND GOD SAID,
‘Let there be visible light, but also ultraviolet, infrared and an entire electromagnetic spectrum of longer and shorter wavelengths’” (not an exact quote). What we humans call
light
is the mere, thin slice of the solar energy spectrum that our eyes are capable of detecting. But in a broader sense, the word “light” really requires a more exact specification.

The light ovens contain banks of specially designed, long-life, 1500-watt halogen lamps that are not vastly different from the halogen lamps in many modern light fixtures. But only about 10 percent of a household halogen lamp’s energy output is visible light; 70 percent is infrared radiation and the remaining 20 percent is heat. The light ovens’ halogen lamps produce a secret mixture of visible light, various infrared wavelengths, and heat. It’s the combination of all three that does the cooking.

(Regardless of what many science books may tell you, infrared radiation is not heat; it’s a form of radiant energy that is converted to heat only when absorbed by an object. I call it “heat in transit.” The sun’s infrared radiation isn’t heat until it is absorbed by the roof of your car. The “heat lamp” that some restaurants use to hold your plated food until the server comes back from vacation is sending out infrared radiation, and the food is warmed by absorbing that radiation.)

The light ovens’ visible and near-visible light do indeed penetrate meat to some extent—you can shine a flashlight through your thumb in a dark room. And they aren’t absorbed by water molecules as microwaves are, so they can deposit all their energy directly into the solid portions of the food, rather than wasting their energy by making hot water first. Some of the wavelengths put out by the halogen lamps can penetrate foods up to three-or four-tenths of an inch. That may not sound like a lot, but the deposited heat then gets conducted deeper into the food from there. And the ovens cheat by supplementing the halogen lamps with microwaves, which penetrate more deeply. (You can use the light ovens also as independent microwave ovens.)

Meanwhile, the longer-wavelength infrared radiations and the heat are being absorbed in the food’s surface, browning and crisping it—something that microwave ovens can’t do. Ordinary ovens take a long time to brown food because only some of their heat gets to the food by infrared radiation; the rest has to get there through the air, which is a poor conductor of heat. The light oven’s infrared radiation heats the food’s surface directly to a higher temperature than an ordinary oven can, so the browning is faster.

Speed, in fact, is the main selling point of light ovens. When GE’s market research teams asked what consumers wanted most in their cooking appliances, the top 3 answers they got were speed, speed, and speed. People said they would love to be able to roast a whole chicken in 20 minutes and broil a steak in nine.

What’s really remarkable about the light ovens is their computer technology. A microprocessor driven by proprietary software programs the on-off cycling of the lamps and the microwave generator in a carefully worked out sequence for the optimal cooking of each dish. GE’s market research discovered that 90 percent of all American consumers’ cooking entailed only 80 recipes (no comment), so these 80 recipes are programmed into the oven’s data bank for pushbutton cooking. Just punch in what kind of steak you have, its thickness and weight and how you want it done, and it’s on your plate before you can say grace.

Now if we only had a computer that would dispense with all of that time-wasting soft music, candlelight, conversation, and wine.

HIGH-TECH, LOW-TECH, NO-TECH

WHY CRACKERS ARE HOLEY

W
hy do crackers and matzos have all those little holes in them?

Saltines, Wheat Thins, Triscuits, Ritz Crackers, grahams, you name it—there’s hardly a cracker anywhere that doesn’t have a pattern of little holes in it.

The makers of matzos, the unleavened flatbread of the Jewish Passover, seem to have gone hog wild (you should excuse the expression) on perforations. Matzos are much hole-ier than secular crackers. But it’s not just a tradition; it’s for a very practical purpose. And no, the 18 holes in a Keebler Club cracker are not a golf course for the elves.

According to a spokesperson at Keebler, there’s a sort of mystique about cracker holes that occupies the minds of people who seem to have very little to do. They’re prone to calling Keebler’s customer relations line to ask questions such as, “Why are there 13 holes in saltines, while graham crackers have various numbers and a Cheez-It has a sole hole?” The answer: “It just turns out that way.”

Here’s a primer on the science of crackerpuncture.

When you’re whipping up a 1,000-pound batch of dough by putting flour and water into an enormous mixer, as they do down at the cracker factory, there’s just no way to avoid getting some air beaten into the mix. Then, when you roll the dough out real thin and put it into a hot oven (saltines are baked at 650 to 700ºF), the trapped air bubbles will expand into bulges and can even explode. Air expands when heated because the molecules are moving faster and pushing harder against their confines.

Besides being unsightly, thin-skinned bulges can bake too fast, scorching before the rest of the dough is done. And if they burst, they leave pockmarks and craters in the surface. A cracker that looks like a scorched, foxhole-riddled battlefield makes a very poor impression on the tea table.

So just before a thin sheet of dough goes into the oven, a “docker”—a big cylinder with spikes or pins sticking out—rolls over its surface. The pins puncture the air bubbles, leaving those telltale pinholes in the dough. The pins are spaced differently for different kinds of crackers, depending on their ingredients, the baking temperature, and the desired final appearance. On saltines, for example, consumers seem to prefer a gentle, rolling-hills terrain, so some bubbles are allowed to billow between the dimples. And those square little Cheez-Its, with their one central hole, have the look of a punched pillow.

If that isn’t already more than you want to know about cracker holes, consider this: In crackers that contain leavening agents such as baking soda, the rising, expanding dough will partially obliterate the holes while resting or baking. But they’ll usually still be there, at least as slight depressions. You think there are no docker holes in Wheat Thins? Hold one up to the light and you’ll see the “fossilized” remains. Even a rugged-surfaced Triscuit has 42 holes in it.

Puncturing bubbles is especially important in matzos, because they’re baked quickly at a very high temperature: 800 to 900ºF. At these temperatures the surface of the dough dries out quickly, and any expanding bubbles would tend to blast through the hardened crust, producing an oven full of kosher shrapnel. So some heavy-duty bubble perforating is in order. It’s done by rolling over the dough sheet with a “stippler,” which is much like a docker, but with close-together lines of teeth. That’s what leaves those parallel furrows.