I have been surprised by questions concerning the use of plastic wraps in the microwave oven. People seem confused because there are several types of plastic wraps now on the market. To further complicate matters, there are wraps labeled "microwaveable" as well as wraps labeled "useful for microwaving."
And at least one new microwave cookbook is recommending PVC (polyvinyl chloride) wrap for covering microwaved food. The result is that consumers are wondering how they can tell one wrap from the others.
To start with, plastic wrap can be divided into two basic types: the regular, thin wrap made of polyethylene, the kind consumers have used for years; and the more modern microwaveable wraps that are thicker, sturdier and more expensive. These heavier wraps can be made of polyvinyl chloride (PVC) or polyvinylidene chloride (PVCD). At least two brands are made from PVC film and two other brands are PVCD film.
How can you tell the types apart? It's not easy, but here are some tips, as well as advice on what film works best for certain kinds of food.
I find it helpful to select plastic wraps based on what I'm microwaving. If I'm cooking vegetables or hors d'oeuvre or heating non-greasy casseroles or leftovers, I know I can probably get away with the lightweight polyethylene wrap. But if microwaving foods with a high fat or sugar content, I usually select heavier PVC or PVCD wraps.
Regular lightweight polyethylene film, which sometimes is labeled "useful for microwaving," should be used with foods that contain little or no fat, since fat reaches high temperatures and can cause the wrap to melt.
PVC and PVCD, sometimes labeled "microwaveable wraps," are almost impossible to tell apart. The only sure way is to ask the manufacturer. Originally used in supermarkets as a clear wrapping for meat, PVC has been praised for its flexibility.
When steam collects between the food and the wrap, the PVC stretches and balloons above the dish. Cooks should be cautious, though, of escaping steam when handling a dish covered with ballooned wrap. Even dishes that are vented by turning back one inch of film at the corner can contain steam.
So-called "microwaveable wraps," which are more dense than polyethylene products, can tolerate high-temperature cooking so are more appropriate for meats and meat combinations such as chili or ribs. Such wraps seal tightest to the dish so that even when vented they hold the steam necessary to cook the inside of the food.
A plastic-wrap-covered casserole can be more tightly sealed than one with a standard lid. In fact, since such a tight seal forms, manufacturers recommend that all plastic wrap be vented when applied to the top of a microwave cooking dish. Manufacturers also suggest that when uncovering a container, place the vented area away from you before peeling back the plastic adjacent to the vented area. This method can partly dissipate the rush of steam released when the plastic is removed.
It is a good idea to consider the phenomenon of trapped steam when choosing a wrap. Personally, I prefer wax paper to plastic wrap for individual foods such as ears of corn. In the absence of a container to vent, the tight covering of plastic makes a very hot, steamy bundle to contend with.
Another earlier recommendation by some microwave teachers was to puncture plastic wrap instead of applying it in a vented manner. This technique has been abandoned because the plastic may further tear or split.
Oven cooking bags made of a kind of nylon also are microwaveable, as are some of the sealable bags for freezing home-prepared foods. Check the manufacturer for recommendations.
When making the following entree, I use heavy-duty PVC or PVCD plastic wrap to cover the fish. Since fish fillets are uneven in thickness, the tight cover, along with the technique of arranging the thickest pieces toward the edges of the dish, helps the steam penetrate the fish evenly.
MEDITERRANEAN SOLE FOOD
2 pounds sole fillets
1 pound tomatoes, peeled and seeded
1/2 teaspoon sugar
1/3 cup finely sliced green onions, including some green top
1/2 cup plus 2 tablespoons butter
2 tablespoons lemon juice
1 teaspoon minced fresh garlic
1/4 teaspoon salt
1/4 teaspoon black pepper
1/4 cup finely chopped parsley
In 12x8-inch dish, arrange fillets with thickest areas toward edges of dish and thin tail-ends overlapping. Cover with heavy-duty microwaveable plastic wrap. Microwave at HIGH (100% power) 10 to 13 minutes, just until thin areas of fish look opaque. (Some center areas will remain translucent but will complete cooking during standing time.) Let stand, covered, while making sauce.
Chop tomatoes into coarse pieces and sprinkle with sugar. In 1-quart microwave casserole, place onions, 2 tablespoons butter, lemon juice, garlic, salt and pepper. Microwave at HIGH 2 to 4 minutes, just until onions are tender. Add tomatoes and sugar and continue microwaving 1 to 2 minutes, until tomatoes are heated through.
Distribute remaining 1/2 cup butter in chunks evenly over mixture. Let stand few minutes to soften butter, then stir gently. Butter should soften but not melt completely. Spoon sauce and chopped parsley over fish. Makes 6 to 8 servings.