10 common microwave questions

Reprinted from http://aginfo.psu.edu/psa/fw98/food.html

Microwave ovens have become as common in the American home as refrigerators, dishwashers, and remote controls. Some microwave ovens even have a remote control. Almost as common as the appliance are consumer questions about microwave cooking, which is where food scientist Swamy Anantheswaran comes in.

Anantheswaran, who has done extensive research on how microwaves interact with food and other materials, finds that even the most seasoned microwave chefs often don't know exactly why or how the ovens do what they do. Here are 10 of the most common questions Anantheswaran is asked, along with his answers. 1

1. Why does my coffee taste bad and show an oily film when I reheat it?

"Coffee and tea are very sensitive to the time and temperature used to reheat them," Anantheswaran says. "Because microwaves may heat unevenly, the liquid may heat at different rates, which burns some elements in the coffee, leading to off-flavors. The film comes from oils within the coffee or tea, which are responsible for its flavor." 2

2. Why do buns and breads turn soft and chewy when heating a hot dog or a sandwich?

"The hot dog or lunch meat in a sandwich releases moisture very rapidly as it's cooked," Anantheswaran says. "The moisture has to go somewhere, and it gets absorbed by the bread. Overheating and rapid heating also will make bread chewy." 3

3. Do meals cooked in a microwave cool faster than those cooked conventionally?

Actually, microwaved meals stay hot longer," Anantheswaran says. "Microwaves cook from the inside out. As heat on the outside dissipates, the food seems cooler. In reality, it is hotter on the inside. The principle is seen easily by heating a jelly doughnut the outside is relatively cool, whereas the filling may be scalding hot." 4

4. Why does spaghetti or other pasta seem to take longer to reheat?

Pastas only seem to take longer because leftover pasta is usually covered in sauce and stored in containers that reduce the surface area of the food. Pasta also reheats more efficiently if water is added to heat and steam the food. Sauces also are high in salt, which absorbs microwaves, causing the sauce to overcook before the pasta is heated. "Microwave ovens heat more efficiently over a large surface area, so spread the food out on the plate and avoid cooking directly in containers," advises Anantheswaran. "The trick to reheating leftovers is to decrease "Why do my hot dogs explode?"power and add a little moisture. Everyone likes to cook everything on high. What's an extra 60 seconds if the food is cooked more evenly? Don't race your oven. It's as bad for the food as racing a car is for the engine." 5

5. Why does my popcorn burn, and why does the "popcorn" button leave so many kernels unpopped?

Anantheswaran says microwave popcorn pops differently because of such variables as brand of popcorn, brand of oven, quality of the kernels, quality of the bag, age of the product, and whether the product is salted.

Joy Daniel, senior manager of product development for Sharp Electronics Corporation, explains that popcorn buttons differ in two ways. A "timed" popcorn button is designed to cook for a preset time based on the average cooking time for consumer popcorn brands. A "sensor" popcorn button will shut the oven off as soon as it senses a certain level of humidity, indicating the popcorn is fully popped. "Microwave popcorn may have more unpopped kernels because the manufacturers are less concerned with popping all the kernels than with providing the indicated quantity," Daniel says. "The manufacturers include more kernels to make sure the corn pops to a full bag every time." 6

6. What is the best covering for food?

Daniel says paper towels are best for breads, rolls, and muffins. Wax paper works best for vegetables. Lids are best for large quantities of dense foods. 7

7. Why do microwaves heat unevenly?

"Microwaves are absorbed from the outside in," Anantheswaran says. "The heat is absorbed differently depending on the size, shape, and composition of the food. Small cylindrical or spherical foods, such as hot dogs or potatoes, heat most evenly. Rectangular foods, such as packaged dinners, may heat less evenly because the microwaves are hitting the top and the sides, causing the corners to overcook." 8

8. What role does the glass platform play in the cooking process?

Removable glass trays and turntables are easy to clean. Carousel platforms allow more even heating as the food rotates within the oven. They also lift the food, allowing microwaves to penetrate from below, Daniel explains. 9

9. Why does my microwave oven cook meats to a tougher consistency?

"In most cases, meat loses tenderness in a microwave from being cooked too rapidly," Anantheswaran says. "Cooking is a series of chemical reactions, and we have to allow time for each reaction to be completed. I usually cook meat on 50 percent power."

10. Why do my hot dogs and potatoes explode?

Anantheswaran explains that foods with skins, such as potatoes, apples, and hot dogs, build up steam pressure within the center as the microwaves heat them. To prevent bursting food, pierce the skin with a fork or make a small slit along its length.

— John Wall