Navigating the world of long-term food storage can be a little bit tricky. Basic dry goods such as wheat, white rice, rolled oats, dry beans, and potato flakes can be safely stored for 30 years or more under the right conditions. Packaging low-moisture dry goods in air-tight containers with oxygen absorbers extend the quality shelf-life by removing the oxygen and creating a high nitrogen environment.
In this post, we will explore exactly what oxygen absorbers are and how they work. We will look at best practices and how to safely use oxygen absorbers to extend the shelf-life of your stored foods.
An oxygen absorber, also known as an oxygen scavenger, is a porous packet that usually contains iron powder and salt. The oxygen absorber packet works when the moisture in the food and air causes the iron to rust. The chemical reaction is oxidation which results in the removal of oxygen.
Removing the oxygen from stored dry food significantly extends the shelf-life. A low-oxygen environment prevents oxidation and controls insects.
Are oxygen absorbers in stored foods dangerous?
Oxygen absorbers are not edible. The porous packets contain iron powder and salt. Oxygen absorbers will not harm the food and are safe to use in stored foods to extend the shelf life.
Oxygen absorbers are incredibly simple to use. Simply place the new, soft oxygen absorber inside a clean, dry, airtight container with the food product and seal. It is important that the container has an airtight seal that can lock out the oxygen from the environment outside the container.
Why does the oxygen absorber feel warm to the touch?
You may notice that when the chemical reaction starts the oxygen absorber may feel warm to the touch. This is normal during the oxidation process. The warmth may result in condensation forming on the outside of the exterior of the oxygen packet and inside of the storage container. This is not a problem and will go away in a few hours.
If your oxygen absorber has moisture on it, simply wipe it off with a dry cloth before placing it in with the dry goods.
How long does it take the oxygen absorber to work?
The oxygen absorber will usually complete the process in about 4 hours. Personally, I like to observe Mylar bags for 24 hours to ensure that they are sealed and working appropriately.
Why do some of the Mylar bags not look like the oxygen absorbers are working?
Remember that air is typically made up of 21 percent oxygen and 79 percent nitrogen. Nitrogen still takes up space just like oxygen. The oxygen scavengers only remove the oxygen. The Mylar bags should shrink up some but will not usually have a “vacuum-sealed” appearance.
If you are concerned about whether your Mylar bags are appropriately sealed and your oxygen absorbers are working, run through this little checklist.
- Is the Mylar bag high-quality without any pinholes to allow the air to escape?
- Is the seal on the mylar bag secure? Always heat seal Mylar. Zip locks are for convenience after opening and will not maintain an oxygen-free environment. Gently squeeze the bag and listen and feel for any escaping air.
- Are the oxygen absorbers fresh? Are they new? Soft and pliable? Discolored?
- Did you use the correct size oxygen absorber for the container? Oversizing an oxygen absorber is not a problem. The reaction will stop when all the oxygen is removed. However, an oxygen absorber that is too small for the container will be exhausted before all the oxygen is removed. I usually oversize the required oxygen absorber for the container just to be sure.
If you are concerned that the Mylar bag or pouch has not been properly sealed, simply cut a slit in the top of the bag and add a fresh oxygen absorber and reseal it with heat.
Oxygen absorbers are used to preserve the freshness of food during storage by removing dissolved oxygen. Oxygen absorbers perform several important functions when used.
- Prevent insect infestation by creating an environment where insects are unable to survive.
- Reduce rancidity and improve the shelf life of polyunsaturated fats and oils.
- Slow down the growth of microorganisms.
- Prevent oxidation of dry goods.
- Reduce loss of Vitamins A, C, and E.
- Inhibit the growth of molds, mildew, and bacteria (aerobic pathogens).
- Preserve original taste, texture, aroma, color, and flavor longer.
- Prevent oxidation of fats and oils.
- Eliminate the need for additives such as sulfur dioxide, sorbates, benzoates, BHA, or BHT for food preservation.
Oxygen absorbers reduce the amount of oxygen to about 0.01%. The remaining nitrogen is inert. The reduced oxygen environment prevents the oxidation of the food during storage.
Proper packaging is important to ensure that the air in the container remains free from oxygen. The ideal containers will create a true oxygen barrier for the longest shelf-life.
What are the best containers to use with oxygen absorbers?
Ideal containers to use with oxygen absorbers are non-permeable and protect any oxygen in the environment from seeping into the container over time. The longest shelf life will be achieved if the container is made from materials that are non-permeable such as metal, glass, or Mylar.
Metal cans, Mylar bags, foil pouches, glass canning jars, and PET/PETE plastic bottles are all acceptable containers to use with oxygen absorbers. Learn more about using these containers to package your longer-term food storage in these articles.
Plastic is permeable and will allow for the slow transmission of oxygen through the walls over time. PETE plastic bottles will maintain an oxygen level of less than 1 percent for at least one year. Plastic buckets can be lined with a Mylar bag to create an effective oxygen barrier which will help to protect the food in long-term storage.
Vacuum sealing is also an option to remove oxygen from a container to extend the life of stored foods. Before you decide which route to take consider the following benefits that oxygen absorbers have over vacuum sealing.
- Oxygen absorbers take the oxygen level down to 0.01% while vacuum sealing removes a significant amount of the air but does not target the oxygen. Vacuum sealers are unable to bring the oxygen level down to 0.01%. High-quality vacuum sealers will remove more of the air so it pays to invest in high quality if you are going to vacuum seal.
- Food is not crushed or damaged when using oxygen absorbers.
- Fine flours are not a problem when preserving with oxygen absorbers as when vacuum sealing.
Oxygen absorbers remove all of the oxygen and leave the nitrogen, so it is not necessary to use both oxygen absorbers and vacuum seal unless your goal is to minimize the size of the packaging.
There are sometimes that I will use both oxygen absorbers and vacuum seal mason jars when I am packaging freeze-dried foods. I vacuum seal only to ensure that the lids on the mason jars are secured. Vacuum sealing alone is not recommended for preserving freeze-dried foods.
Individual packets of oxygen absorbers are available in a variety of sizes from 20cc to 2500cc. CC or cubic centimeters refers to the amount of oxygen-absorbing capacity each individual packet has. The size oxygen absorber required to absorb all of the oxygen in the container may vary depending on the contents.
Some dry goods such as wheat, rice, rolled oats, or flour take up more space in the container and leave a low volume of oxygen to be removed. Pasta, dry beans, and pet food will leave more air space in the container and will require a more powerful oxygen absorber.
I like to err on the side of caution and use the higher amount just to make sure that the job gets done right. You can oversize an oxygen absorber without any negative consequences. However, if you use one that is just a little bit too small, the job won’t get done correctly. You may have oxygen remaining in the container allowing for the oxidation of the food and the growth of insects.
Personally, I usually purchase 400cc or 500cc oxygen absorbers and use them for everything one gallon or smaller. If I’m sealing something in a large bucket I just use 3 to 5 of them depending on the circumstances. The cost is not significantly different but this means that I don’t have a bunch of different sizes opened and waiting to be used.
Here is my quick reference chart for determining the size of the oxygen absorber that you need.
(Low air volume in the container)
|Dry Beans/Pasta/Pet Food
(High air volume in the container)
To calculate the exact size of the oxygen absorber you need for your project, simply subtract the product’s weight from the packaging capacity. Remember that 21% of air is made up of oxygen and most of the remaining air is nitrogen which is ideal for storing food.
Oxygen in a container (ml) = (Air volume in a container (ml) – the weight of the product (g)/specific gravity) x 0.21.
Oxygen absorbers will take about 4 hours to remove the amount of oxygen they are rated to absorb. If all the oxygen is absorbed before the iron is used up, the chemical reaction stops until more oxygen is introduced.
This can be handy when I package dry goods in mason jars. I usually use 300-cc, 400-cc, or 500-cc oxygen absorbers for most of my dry goods because it is easier to have one size open at a time. A one-quart bottle only requires a 100 cc oxygen absorber. If I use a 400-cc oxygen absorber in a mason jar of dehydrated celery, the first few times that I use food out of that jar it will continue to remove the oxygen and reseal the jar.
Once I have sealed dry goods in a Mylar bag with an oxygen absorber, I leave the package out for 12-24 hours and inspect the filled Mylar bag to make sure that it has reduced in size. It will occasionally have a similar appearance to a vacuum-sealed bag but not always. The bag should have reduced in size but may not shrink significantly.
If the Mylar bag has not reduced in size after a day, it may be due to one of the following issues.
- Percentage of oxygen in the air. Room air is roughly 21 percent oxygen and 79 percent nitrogen. Only the nitrogen remains in the container. (No action needed)
- Tiny pinholes in the Mylar. (Contact manufacturer for replacement)
- Potential leak in the seal. Gently squeeze. Look and listen for escaping air. (Reseal if necessary)
- The oxygen absorber was undersized for the container. This could result in all of the iron powder rusting before the oxygen was absorbed. (Cut a small slit in the top of the Mylar bag. Place an appropriately sized fresh oxygen absorber in the package. Heat seal closed.)
- Bad oxygen absorber used. Fresh oxygen absorbers will be pliable and warm up when exposed to oxygen. They should be placed in the container as soon as possible and the package sealed immediately. Oxygen absorbers become useless if left exposed to room air. (Cut a small slit in the top of the Mylar bag. Place a fresh oxygen absorber in the package. Heat seal closed.)
A spent or exhausted oxygen absorber will turn spotty, brown, and hard or clumpy. New oxygen absorbers will be soft, and the powder will be pink or gray.
Some oxygen absorbers are packaged with a small color indicator that indicates if the package has been compromised. The color indicator will be pink if the package is intact. Once that indicator has been exposed to air it will turn blue or purple. The indicator does not mean that the absorbers are bad. Simply, the indicator has been exposed to oxygen.
Dry goods that are low in moisture (10% or less) and low in oil are the best candidates for long-term storage with an oxygen absorber. Examples include; wheat berries, white rice, rolled oats, dried beans, dried corn, dried potato flakes, dried onions, dried carrots, and non-fat dry powdered milk.
Warning: Botulism poisoning may result from packaging foods with high moisture content in reduced oxygen packaging. Just because someone else does it doesn’t mean that it is a safe practice.
How do I find the moisture content of dry goods?
Moisture levels in dry goods can vary. There are general guidelines but if you are curious simply contact the manufacturer or visit the US Department of Agriculture Agricultural Research Service Website.
How do I find the oil or fat content of dry goods?
Whole grains, such as brown rice, tend to be higher in fat content along with nuts and seeds. This healthy fat will reduce the shelf life because the fats tend to go rancid in storage. Reducing the level of oxygen in the container can prevent oxidation and slow down rancidity. Storing at cooler temperatures will also slow down that process.
You can learn the fat or oil content of a specific product by contacting the manufacturer or visiting the US Department of Agriculture Agricultural Research Service Website.
Products containing fats and oil such as granola or nuts have a short shelf life of 6-24 months, longer if stored in a cool location. Some manufacturers recommend using oxygen absorbers to prolong the shelf life and reduce the rancidity of foods that are high in oil such as nuts, brown rice, etc. Storage of these items should only be short-term.
You will find oxygen absorbers in many foods such as bread, cookies, nuts, candy, coffee, tea, cheese, dairy products, smoked and cured meats, dried fruits and vegetables, fresh pasta, dry pet food, vitamins, and the list goes on. These are placed in the items to extend a short shelf life. That does not mean that they are safe for long-term storage.
Do not use oxygen absorbers in sugar, baking soda, baking powder, or salt. Packaging these items with an oxygen absorber will make them turn clumpy or hard.
Sugar, baking soda, baking powder, and salt do not require a reduced oxygen environment for preservation. They can be stored indefinitely in an airtight container (such as a heat-sealed Mylar bag or glass jar) indefinitely without an oxygen absorber.
Do not use oxygen absorbers in food products that are high in moisture!
The recommended moisture content for safe long-term storage of dry goods is 10 percent or less and low in fat. You can determine the moisture content of a food by contacting the manufacturer or looking it up on the USDA Agricultural Research Service.
Not all foods are listed on this site, but this is a great resource to find the moisture content of many basic foods.
The reaction begins as soon as the iron in the packet is exposed to oxygen. It is best to package the oxygen absorber within 15-30 minutes. Make sure that you place unused oxygen absorbers into an airtight glass jar, seal them in a Mylar pouch, or vacuum seal them in a bag immediately.
The chemical reaction created by the oxidation of the iron does not stop until all of the oxygen has been removed from the environment. Placing the packet in a small airtight container quickly means that there may still be enough charge left to use. It is a good idea to use oxygen absorbers that have been removed from their original packaging within 6 months.
Once the oxygen is used up in the container the oxidation process stops until it is exposed to oxygen again. This is one of the benefits of oxygen absorbers. They will continue to work until they are “fully loaded” or all the iron has been rusted.
What is the shelf life of unopened oxygen absorber packets?
Wallaby, a manufacturer of oxygen absorbers, states that the self-life of unopened oxygen absorbers is usually about 2 years in the sealed state. So, you have 2 years to use them (if you leave them in the original packaging). Once they have been opened, you should use them within 6 months.
Oxygen absorbers are used in the storage of dry goods for long-term food storage to reduce oxygen. Ideal candidates for long-term food storage should be 10 percent moisture or less so a desiccant packet should not be necessary.
Desiccant packets do not have the ability to reduce the moisture in dry goods to an acceptable level. It would take a significant amount of desiccant to make any difference at all. Do not purchase high-moisture foods and expect to manage the moisture with a moisture absorber. It does not work that way.
Desiccant packets can help to control environmental moisture if you are packaging dry food storage in a humid climate.
It is best to avoid using an oxygen absorber and a desiccant packet together in the same container.
Oxygen absorbers require a small amount of moisture to sustain the reaction that removes the oxygen. Adding a desiccant packet may prevent the oxygen absorber from working properly and may result in the failure to remove oxygen.
If you do find it necessary to use both a desiccant packet and an oxygen absorber in the same container, place the desiccant in the bottom, fill the container, and then put the oxygen absorber on the top before sealing it tight. Do not place an oxygen absorber and desiccant packet near each other in the packaged dry goods.
Do NOT use desiccant packets in salt, sugar, flour, or fine powders.
Never use desiccant to salt, sugar, flour, finely milled products, or powdered items. These dry goods require a small amount of moisture and may turn hard if that moisture is removed.
I’m a huge fan of using oxygen absorbers in my dry goods for long-term storage. Oxygen absorbers make a noticeable difference in the quality and prevent insect infestation in stored grains. Best of all they are incredibly simple to use.
I’m a fan of the oxygen absorbers sold by Wallaby. They sell oxygen absorbers in bags of 100, but they are packaged in smaller packets of 10 each for convenience. The larger oxygen absorbers are packaged individually. Use the promo code PROVIDENT5 to get a discounted price.
You can learn more about building both your short-term and long-term food storage in these posts.
Thanks for being part of the solution!
Jonathan and Kylene Jones