Wrapped Up

FREEZER PAPER is a heavy, white kraft (German for "strength") paper, coated on one side with plastic to make it water- and vapor-proof, thereby preventing the water-vapor losses that cause "freezer burn" in frozen foods. It is relatively difficult to wrap food in, however, and I find other, more resilient vapor-proof coverings such as aluminum foil and plastic wraps to be more convenient. Tight, careful wrapping in these materials also may prevent freezer burn .

ALUMINUM FOIL The virtues of aluminum foil stem mainly from its formability -- it retains whatever shape it is pressed into -- and its resistance to temperatures up to 1,220 degrees, at which point it melts. But being a metal, it cannot be used in a microwave oven except in very limited situations.

Aluminum foil is made by rolling 98.5-percent pure molten aluminum between large, chilled rollers that solidify it. The final product has a dull side and a shiny side, because in the final rolling, two sheets are sandwiched and rolled together. The sides in contact with the polished rollers come out shiny. It makes no difference which side is in contact with your food.

PLASTIC WRAPS Kitchen plastic wraps may be made of polyethylene (Glad Cling Wrap, Handi-Wrap)or polyvinyl chloride (Reynolds Plastic Wrap). Saran has recently changed its plastic from polyvinylidene chloride (Original Saran Wrap) to polyethylene (Saran Premium Wrap) because some people fear anything with chlorine in it. The Premium Wrap has the coolest hassle-free dispensing and cutting mechanism you ever saw.

I won't go into the Internet urban-legend allegations of the dire consequences of using plastics in the microwave oven because I wrote about that in my March 30 column. All I'll say here is: Use whatever brand you like. It won't kill you.

But there's an ingenious sticky-on-one-side plastic wrap called Glad Press'n Seal that, according to its legalistic patent description, prevents "inadvertent adherence." That is, it won't stick to anything (including itself) until you deliberately place it on a surface and press it. The secret is that it has microscopic spikes on the sticky side that keep the adhesive away from the surface to be covered until you deliberately crush the spikes by pressing. The film makes a tight, spill-proof seal around the rim of any clean container made of glass, porcelain, plastic, wood or metal.

And speaking of sticking, Reynolds produces Reynolds Wrap Release Non-Stick Aluminum Foil, an aluminum foil with nonstick coating on one side. Yes, folks, now when you reheat a slice of pizza in the oven on this foil, the dripping cheese won't stick.

Civilization has been waiting a long time for this development.

Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2: Further Adventures in Kitchen Science" (W.W. Norton). He can be reached atwolke@pitt.edu.