Oxygen Absorbers - Their Use And Function

Oxygen absorbers are little packets of iron powder packaged in a material that keeps the iron in, but allows oxygen and moisture to enter and be absorbed. Moisture and air (oxygen) are two factors that destroy the value of dehydrated and freeze-dried foods. The iron absorbs the oxygen causing the iron to rust. As it rusts, or oxidizes, it absorbs any oxygen that may be present.

Air is 78% nitrogen, 21% oxygen, and 1% a mixture of other gases, mostly argon. Because air is colorless, odorless, and tasteless, we often overlook it as a cause of food spoilage. While it is essential for life, it has a detrimental effect on color, flavor, vitamin content, and fats of stored foods. Oxygen present in stored foods enhances the growth of insects and microorganisms such as bacteria, mold, yeast, and enzymes present in foods react with oxygen to speed up the spoilage process. Oxidation itself works primarily on the fats in foods, causing them to become rancid and develop acrid, unpleasant off-flavors. By removing the oxygen all that remains is nitrogen, thus nitrogen packed food.

Moisture is present in all foods, even dry beans and grains, but there are two kinds of water - bound and free - and they behave differently. Bound water is physically attached, or bound, to large molecules in the food and is not available to contribute to the growth of insects or microorganisms or to take part in chemical reactions. So it is the "free" water that causes trouble such as molding of grains, caking and lumping of flour, etc. Foods that have been dehydrated or freeze-dried have had most or all of the free water removed, so that source of spoilage is gone. They are generally packed in cans or metallized bags to prevent light from reaching them. With the use of oxygen absorbers, the three main sources of spoilage - light, oxygen, and moisture - are all controlled.

Oxygen absorbers actually remove oxygen more effectively than vacuum packaging, as they remove only the oxygen rather than all the air. To be effective, packets should be used only in containers that are a barrier against moisture and oxygen.

Nitrogen, the main component of air, does not have the negative effect that oxygen has. In fact, a "nitrogen flush" is often used to force the oxygen out of a product before it is sealed for storage. Nitrogen does not allow for the growth of insects or microbes, nor does it contribute to food spoilage in any way or affect the taste or nutrition of foods. Dry foods are protected well in a nitrogen environment. Even when a nitrogen flush has been done, it is still wise to include an oxygen absorber packet inside the container.

Foods that are appropriate for storage with oxygen absorbers are those that are low in moisture and fat content. Moisture needs to be about 10% or less. If it is higher than that, storing products in reduced oxygen packaging can possibly result in botulism poisoning.

Containers that work well with oxygen absorbers are metal cans with seamed lids, quality foil pouches such as metallized bags, PETE plastic bottles with airtight, screw-on lids, and glass canning jars with metal lids that have gaskets. Plastic containers other than those identified as PETE or PET under the recycling triangle are not appropriate to use.

Oxygen absorber packets come in different sizes, two of the most common being 500cc and 2000cc. The size depends upon the size of the container and the "void area," the empty space between the food particles and between the top of the food and the lid of the container. Foods that are powdery such as flour, cinnamon, or cheese blend obviously will have less space between particles than foods that are in larger, uneven shapes such as freeze-dried broccoli or mushrooms. Some companies that manufacture absorber packets rate them according to their oxygen absorption capacity in milliliters, while others do so by the equivalent air volume (the actual total amount of air between the product pieces).

To use oxygen absorbers properly, do not plan to package more at one session than you can do in about 20 minutes, as exposure to room air will speed the demise of the absorbers. (Some absorber packages appear pink when viable and turn purple or blue when they are used up.) Plan ahead of time how you are going to store any unused absorbers. They can be stored in glass jars that have a lid and ring seal. Use the smallest jar possible and pack them in tightly so that they don?t have as much oxygen to deal with. A one-pint jar will hold 25 absorbers. Another method is to heat-seal them back in the bag they came in. Most companies do not recommend it, but if you choose to store them in zip-lock freezer bags, realize that you must use them within the next few months, as these will slowly admit oxygen and shorten the lifespan of the absorbers.

Place on a tray the number of absorbers you expect to need for one batch of packaging. Use one absorber per package of food, and work as quickly as possible to preserve the life of the absorbers. When you are ready to do another batch, remove enough absorbers from their bag or jar for that batch. Try not to keep opening their container for a few at a time.

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This article is sponsored by Emergency Essentials.
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