Published February 1, 2009. From Cook's Country.
Our tests showed that wraps either cling or keep food fresh—not both.
Plastic wrap is essential for storing, freezing, and keeping food fresh, but using it can drive you crazy: The roll rips and wraps around itself; the plastic clings to itself more than the dish or won't stick at all; the box falls apart, letting the roll drop out; the sharp metal teeth slice more than the plastic—or merely shred it; and most important, it doesn’t keep food from spoiling quickly. Has any brand overcome these failings?
First, we measured strength by pulling foot-long pieces of wrap in a series of sharp, short tugs until they tore or lost their shape. Two brands shone because they were almost impossible to destroy.
To test the ability of the wraps to cling, we placed 8 ounces of grapes in plastic, metal, and glass bowls and covered each bowl with one sheet of wrap. With a few shakes of an inverted bowl, we instantly could see which wraps had the most cling—and which let the grapes fly out. All brands performed well on glass bowls. On metal, some brands failed in as few as three shakes, spilling grapes all over the counter. Others held their grip through all 10 shakes. Plastic bowls presented the biggest challenge, and only a few brands could hold on for even a few shakes.
The most important test measured the ability of the wraps to keep foods fresh. We were looking for an impermeable wrap that prevented air and moisture from passing through. Since it was difficult to quantify “freshness” with a real-world food test (Check for mold? Off smells?), we took a scientific approach. We purchased a bottle of Indicating Drierite (calcium sulfate), an absorbent used in packaging, whose small purple-blue pebbles turn bright pink when exposed to moisture. We put 1 tablespoon of Drierite in small glass bowls covered tightly with a sheet of each wrap. After two days, the Drierite in bowls covered with three of the plastic wraps had turned bright pink, indicating that the wrap had allowed moisture in, which means food would spoil faster. The Drierite under the other wraps lasted more than three weeks without a color change, indicating that these wraps were impermeable. This shocked us: A leading contender had failed. In disbelief, we repeated the test, with the same results. What had happened?
As it turns out, plastic wrap can be made from two distinctly different substances. The earliest plastic wrap was made of PVC (polyvinyl chloride), a highly clinging material. But plasticizers and chlorine in these wraps held a risk of food contamination, so manufacturers came up with safer substitutes. Some stuck with a new food-safe version of PVC; others switched to low-density polyethylene (LDPE). The main difference? PVC clings but is not impermeable; LDPE is impermeable but has far less cling. Our research revealed that three wraps are all made of clingy PVC, and the rest of the lineup is less-clingy LDPE. Another style of LPDE wrap is made with an edible dimpled adhesive. We don’t like this style. While it works well initially, once the seal is broken (say, if you were taking a helping of potato salad out of a bowl), this wrap won’t reattach.
Our testers much preferred packaging with metal teeth on the top edge, inside the cover, to those with teeth on the exposed bottom of the box, which were more apt to snag testers’ clothing and skin. We liked boxes with a sticky pad on the front to hold the sheet, keeping it from rolling back on itself and getting tangled and crumpled. We’ve yet to find perfect packaging.
Clingy PVC wraps are preferable if you are transporting food or are worried about spills and leaks, but to keep foods fresh longer, select plastic wraps made from LDPE and reach for a box of our all-around winner.