The Curious Cook
On Food and Zapping
By HAROLD McGEE
Published: April 2, 2008
THE microwave oven is a quirky appliance. Sure, it cooks and reheats many foods quickly and well, and in containers that can go right to the table or come right from the fridge. But it can also cause a mug of hot water to erupt scaldingly, char nuts and breads on the inside, and blow up eggs and butter.
Times Topics: Microwave OvensTo make the most of the microwave, it helps to know its quirks, and ways to work around them.
The strange powers of the microwave arise from the basic fact that it cooks indirectly, with radio energy. Conventional baking, broiling, boiling or frying transmits a particular level of heat directly to the food. But when we zap, the air in the microwave oven barely gets warm. Instead, the oven emits radio waves that penetrate the food from all directions and generate heat within the food itself ó until the oven turns off.
Of the substances in food, water is especially quick to absorb microwave energy. When it does, the water molecules move faster, crash into the more sluggish proteins, carbohydrates and fats, and jolt them into motion, raising the temperature of the food as a whole.
This constant heat generation can create temperatures beyond the boiling point. That often means trouble.
Microwave an egg in a shell long enough to turn some of its moisture into steam ó about a minute ó and the pressure shatters it. Microwave butter long enough to melt it, then continue heating the water that settles to the bottom, and that water will boil and splatter butterfat all over the oven. Microwave a mug of water long enough, and it can superheat past the boiling point without bubbling, then bubble violently the moment you disturb it.
So keep close tabs on cooking, and turn off the oven as soon as the food is done. Medium and low oven settings are useful because they pulse the radio waves on and off and slow the heating so that itís easier to control.
The lack of precise temperature control in a microwave means that itís not ideal for meats, fish or egg dishes, which toughen when slightly overcooked. Even when reheating stews, it is best to remove the meat or fish, microwave the liquid to a boil, then recombine.
Because the microwave oven energizes the foodís moisture first, there is a general drying effect: it causes moisture to evaporate out of the food. So itís usually best to cook in a container that will retain most of the vapor around the food surface. Leave small openings for some vapor to escape, otherwise the container will burst open.
Thanks to their moisture, foods generally absorb microwaves and heat up much faster than their containers. Some ceramic containers can get very hot thanks to metal compounds in their clay or glaze. Special plastic steamers or plastic wrap are popular, but I prefer glass or ceramic ovenware, either with their own lids or with a plate on top.
Plastics are harder to clean of residual colors and flavors, and may leach undesirable chemicals into the food. They shouldnít be used with oils or fats, which keep foods moist but can get hot enough to melt the plastic.
Despite general warnings against using metal, metal containers and aluminum foil arenít dangerous. They reflect microwaves away from foods and so slow their heating. Thatís sometimes useful for preventing the edges of foods, like fish fillets or asparagus tips, from overcooking. Just donít put foil or bowls too close to each other or to the oven walls, since that can cause sparking.
Metal fork tines are especially likely to spark. I learned that when I melted chocolate and left a fork in the glass bowl. The whole batch tasted burned.
Microwave energy can instantly penetrate food to a depth of about an inch, instead of slowly working its way in from the surface by conduction. If the food is less than an inch thick, itís essentially cooking all at once. That rapid heating generally means that the food retains more of its vitamins than it does when itís boiled, steamed or baked.
On the other hand, microwave energy doesnít build up at the surface the way ordinary heat does, so it doesnít brown the food; its effect is more like steaming. Only when food dries out can microwaves cause browning. And that can happen out of sight, and fast.
Itís easy for nuts and stale bread (which microwaving helpfully softens for cutting) to char inside while the outside looks unchanged. The nut or bread surface stays relatively cool while the heat inside keeps building. Low oven settings can help prevent this.
Once you get used to these quirks, youíll come up with some convenient techniques. My current favorites:
POPCORN FLAVORED WITH SPICES In conventional popping, the spices burn. Coat kernels with spices and a little oil, and zap in covered ovenware.
NON-ERUPTING POLENTA Gradual heating eases water absorption, and the polenta bubbles just as it becomes done.
HOT FOAMED MILK FOR COFFEE Put cold milk into a jar, close, and shake until foamy. Open, and microwave until hot.
One last quirk: Microwaves work in the same part of the radio spectrum as cordless phones, Bluetooth devices and wireless home networks. Iíve lost phone connections to oven interference. Sometimes thatís convenient, too.
Friends donít let friends buy spices at American grocery stores!
Mikeís Hot Spicy Food Recipes