How to Remove Air from a Freezer Bag

Air left in a bag is the leading cause of freezer burn. Moisture on the food’s surface moves into that air, collects as frost on the inside of the bag, and dries out the food. Oxygen carried by the air also speeds up rancidity in fat; that is why fatty fish and ground meat are among the foods that spoil fastest in a bag with air left inside. Pressing the bag by hand and sealing it removes most of the air, but some always remains in the corners and folds around the food. Even this small amount of air can make a difference in a package kept for months.

The water displacement method removes this remaining air and requires no tools. Fill a large bowl or sink with water. Place the food in a zipper freezer bag and close the zipper, leaving one corner open. Slowly lower the bag into the water with the open corner kept above the surface. As the water rises, it applies pressure from outside; the bag clings to the food and the air inside escapes through the open corner. Lower the bag slowly: if it is plunged in quickly, water may enter through the opening instead of air escaping.

As the water approaches the opening of the bag, fully seal the zipper while it is still above the waterline, then remove the bag from the water. The resulting package is quite close to what a vacuum sealer produces. Two details determine the result: the area where the zipper closes must stay dry, and the bag must actually be a freezer bag. A wet zipper may not seal completely; a thin grocery bag can be punctured by the water pressure and let water in. Before lowering the bag, wipe the zipper strip with a dry cloth.

The method does not work equally well for every food. It works very well for solid foods such as meat, chicken, fish, cheese, slices of bread, and cooked vegetables. With liquids such as soup and sauce, the contents spill out of the opening as the bag is lowered into the water. Freeze liquids first in a container or in a flat bag, then transfer them to a bag with the air removed once they are solid. Do not use the method for light foods such as powders and flour, because the powder can scatter with the escaping air and stick to the zipper strip, preventing it from closing.

When you do not want to use water, there is a second option: leave the zipper open just wide enough for a straw, suck out the remaining air through the straw, and close the zipper as you remove the straw. Do not use this method for raw meat, poultry, or fish, since raw juices can be drawn into your mouth. This method does not work as well as water displacement, but it is noticeably better than pressing the bag by hand and can also be used with liquids. Whichever method you choose, writing the contents and date on the package is part of the process; a bag with its air removed is still lost if no one recognizes it. Write on the bag while it is still empty and lying flat; writing on a full bag is difficult and the result is hard to read.