By Bonnie S. Benwick
Washington Post Staff Writer
Wednesday, September 10, 2008

When it comes to stashing food in the freezer, this much is true: Everybody does it, but not everybody has gotten the hang of it.

After all, freezing food properly takes a certain know-how. Understanding which foods freeze well and which ones can be finicky is just the first step. The choice of wrapping or container can make or break any attempt to keep frozen food at its best.

To learn what works, we put foods into a variety of containers, wraps and bags, storing them in a chest freezer with the recommended climate of zero degrees for short and long periods of time. It was an ideal environment, one that not all cooks can provide because of space or cost constraints. If you have access only to a refrigerator freezer, you might be limited to short-term freezing of no more than a month or two. Daily delving into a standard refrigerator's coldest storage compartment causes temperature fluctuations that can negatively affect freezing conditions; how items are stacked and how full the refrigerator freezer is (at least two-thirds full is best) have an impact as well.

The basics of freezing food are pretty well covered by the USDA's Food Safety and Inspection Service, found at http://www.fsis.usda.gov/FactSheets/Focus_On_Freezing/index.asp, which also lists freezer storage times for 16 categories of foods. The summary says it is important to freeze food as quickly as possible to maintain the highest quality: Slow freezing creates large ice crystals that can damage emulsions and cell walls within foods.

Reducing the amount of air around food is equally important, which is why items in vacuum-sealed pouches generally have a longer freezer life than those that are not carefully wrapped in plastic and/or aluminum foil, or enclosed in containers or bags with lots of air inside.

Plastics provide the most convenient ways for us to freeze foods these days; all but one of the materials we tested were some form of polyethylene, polypropylene or polycarbonate (see accompanying sidebar for brands).

Polyethylene is used to make food storage bags and most plastic, or cling, wraps. It is the most permeable of the three types, allowing some air and moisture to get next to food. It can offer freezer protection but tends to stiffen and become less airtight over time. That's why we find better results when items such as raw chicken parts or steak are first wrapped in plastic wrap and then sealed inside plastic food storage bags made for the freezer.

Freezer-quality, food-safe plastic storage bags, made of a heavier polyethylene than ordinary plastic sandwich bags, are inexpensive and readily available, but they are more effective as sole protection for short-term, rather than long-term, freezer storage. Some can leak air over time or lose their seal.

Polypropylene and polycarbonate are used to make lots of freezer-safe plastic containers. Polycarbonate is less permeable and more rigid, which might make it a better choice for freezing in the long term (and might allow for greater microwave and dishwasher use). It is also optically clear yet shatter-resistant and lightweight. Both kinds of containers work best with excess air eliminated. The manufacturers claimed that all the products we tested are free of bisphenol A (BPA), a chemical that is used in the making of some food-safe plastics. Though some studies have linked BPA with health problems, experts at the American Chemistry Council, based in Arlington, say all the food-safe plastics used by the American public, even those that contain the chemical, are sound.

A survey done two years ago by the council involving consumers' knowledge about kitchen practicalities and plastics showed that prevention of freezer burn ranked highest on their list of concerns about food storage, says Jennifer Killinger, director of industry and consumer outreach for the group's plastics division. (There were no BPA-related questions in that polling.)

Consumers should invest in a "grown-up" set of durable plastic containers in multiple sizes with resealable lids, Killinger says, and not rely on the cleaned-out cottage cheese or yogurt containers that can warp over time when frozen. She also advises reading container labels for specific guidelines on whether they should be used in the microwave, dishwasher and freezer.

Glass containers for freezer use have experienced a slight revival, perhaps because of the public's qualms about plastics in general. Mona Williams, national vice president of buying for the Container Store, says she has noticed an uptick in sales in the past six months, although the chain still carries more plastic than glass containers for freezer use. We included one type of glass container in our testing.

Models that feature clip-on or snap-on lid fasteners are good sellers now, Williams says, because they are more user-friendly for folks with limited dexterity or hand strength. Consumers also want a range of sizes and shapes, and they are particular about how the containers' contents can be labeled.

There's more to consider. The fine print on packaging for some plastic containers warns against using them to store hot foods or foods made with fats or oils. "That's not something most people realize," says Susie Theodorou, author of the 2007 guide and cookbook "Can I Freeze It?" The heat and oils may cause the plastic to deform or deflate or interact with the food.

In the end, our testing reinforced common wisdoms (read the packaging and labels for best use, etc.), and it revealed useful distinctions among the products, especially with regard to what would happen to them next, be it microwaving or immediate defrosting:

· Containers filled with food to be frozen need an inch of head space, allowing for expansion. And for optimum freezing and defrosting, food should be no more than two inches deep, which suggests the need to keep a variety of freezer container and bag sizes on hand.

Filling a Ziploc bag with six pounds of homemade cassoulet might seem like an efficient way to handle leftovers quickly, but defrosting that misshapen hunk takes days in the refrigerator. Better to portion among several smaller containers, label and date them.

· A few minutes' time taken to wrap, seal and store properly will reduce food waste and maintain better food quality.

· Recheck the seals on plastic bags or foods vacuum-sealed at home after they've spent one month in the freezer. Repackage foods in new bags, if necessary.

· Placing newly purchased bags of frozen fruits and vegetables inside a slightly larger, freezer-safe bag reduced or eliminated the formation of ice crystals and extended their freezer shelf life by several months. There was no need of further protection for manufacturer's vacuum-sealed pouches of raw meats.