There is lots of information out there about oxygen absorbers and unfortunately some pretty common misconceptions as well. I have pooled info from many of the largest manufacturers of oxygen absorbers and food storage companies to help understand what an oxygen absorber does, how they work, how to use them properly and how big (or small) size oxygen absorbers you need to use. This information combined with other information on this site, can help you reach the longest term food storage possible. (see food storage tips and Mylar 101 for additional hints). Oxygen absorbers are considered non-toxic and Generally Recognized as Safe (GRAS) by the FDA because they remove oxygen without chemicals.
What is an OA (Oxygen Absorber), and how does it work?
Oxygen absorbers (sometimes confused with silica or desiccant packets) essentially trap oxygen in their environment until they have reached their capacity. This is why an oxygen absorber, once opened, should be placed immediately into a food storage bag or storage container and sealed as quickly as possible. If left out too long, the oxygen absorber will reach its usable capacity for absorption, sometimes in 10-15 minutes, and not function properly when and where it’s needed. Oxygen absorbers only absorb oxygen (not moisture or air) and will only work as they are intended with fully dried goods.
My bag hasn't collapsed, did my OA fail?
One of the biggest misconceptions is that a sealed food storage bag should collapse or have a “vacuum sealed” look after the oxygen absorber has been used. You should not feel invalidated because your food bag does not look vacuum sealed. The oxygen absorber may reduce some of the volume of the bag, but only eliminates oxygen, not air. Oxygen only makes up 21% of the air inside a food storage bag. Before sealing your bag you can remove additional air and oxygen by reducing the unnecessary volume in the bag. Try to squeeze, move or reposition the contents to reduce the volume. Keep reading the next section to see how you can increase your chances of removing more oxygen.
What size Oxygen absorber do I need?
Oxygen absorbers are made from iron powder and when exposed to oxygen, become iron oxide. Through this process, the oxygen absorber will remove oxygen in its bag, container or area until it is full. Most oxygen absorber packets you see are categorized by cc amount. This refers to the amount of cc’s of oxygen it is capable of removing before it is full. Keep in mind the cc’s of oxygen you need to remove is that of the bag or container filled with contents, not the empty volume of the container or bag. The $1,000,000 question is what size absorber do I need? There are many variables that need to be addressed before answering this question with certainty. With the following information and the charts below, you should be able to get a good idea of the correct size for your needs.
Container size and food type?
The main questions you will need to answer are what type of food you are storing and what sized container or bag you are using as well. The type of food you are storing matters because you need to have some idea of how much oxygen the food is holding as well. “Cc” stands for cubic centimeters. Most containers are measured in mL, but lucky for us, 1cc is the equivalent of 1mL.
The most basic and simple way to figure out the cubic centimeter volume or “cc” is to divide the cc or volume amount by 5 since oxygen is approximately 20% of the air inside the storage container or bag. Here are a few quick references for suggested oxygen absorber sizes. In most cases under 1 gallon, 300cc is sufficient. Keep in mind this is a general suggestion and the recommendations made are assuming the container or bag is full of contents and there are variables that will change the size needed.
You cannot overdo the amount of oxygen absorbers used and in many cases certain foods like flour or pasta hold 50-75% air so take that into consideration. Another reassuring point to this is an overage of absorber size can continue absorbing oxygen in a bag or jar with a small leak for several years. This means that food that would have in most cases been ruined, may be fine after all. Another refreshing fact is that most oxygen absorbers will absorb more than their rating. DO NOT however, try to use this to your advantage. I always encourage freeze dryers to do their own research and/ or consult with the manufacturer of the oxygen absorbers.
For Mylar food storage bags:
Quart Mylar (8x12) = 300cc
Gallon Mylar (10 x 14) = 300cc is usually sufficient. However, sometimes 2 depending on freeze dried food type. If in doubt, use 2!
If you are using Mason Jars, the barrier (glass) around the food cannot be manipulated, so the safest way to judge absorber size for a jar is to assume as if it were empty of contents. Here are the recommendations for mason jars.
½ Pint jar = 50cc
Pint jar = 100cc
Quart jar = 200cc
Gallon jar = 800cc
One more way to dramatically increase your results for removing all or most of the oxygen in your storage bag or container is vacuum sealing. I have the best results with a chamber vacuum sealer. This makes the success rate go up by dramatically removing the amount of volume, air and oxygen that you start with. For example, Let’s assume 2 people are storing an identical food product. They are both using an identical Mylar type storage bag. They are also using the same recipe and using the same size oxygen absorber. One is using a vacuum chamber sealer and one is just putting the food directly into the bag with the absorber. The person that vacuum seals is not only removing most of the volume or air from the space, but is also removing some from the food as well. Oxygen can get embedded or trapped in food and by removing as much oxygen as possible prior to sealing, the oxygen absorber has a far better chance of removing any leftover oxygen, if any.
What do I do with extra Oxygen Absorbers?
When you buy oxygen absorbers they come in packs of 10, 25, 50 and sometimes 100’s or 1000’s even. The problem with having lots of oxygen absorbers is when you are packaging freeze dried food, you rarely use the perfect amount of bags to oxygen absorber ratio. So, what do you do with those extra absorbers? You can’t leave them out or they will be useless in a short period of time. Safe working time is 10-15 minutes, and most absorbers will absorb their full capacity within an hour. There are a couple of options that will keep them good and ready for the next time you are packaging.
The first, is a simple ball/ mason jar with a known working lid. I like to place the color indicator that comes with the absorbers in the jar so I can keep an eye on that as well. The indicator is a small piece of plastic and paper that in most cases, reads pink if the absorbers are working and purple if they are not.
The second way of storing unused oxygen absorbers is to place them into a Mylar food storage bag and seal. I prefer this method only if you are not planning to use them for a while. This method works just as well as a jar, but is a little more tedious and not as convenient. I also try not to waste Mylar bags, as they are pretty expensive and while you can reuse them, you lose a little of the usable bag area every time you open it.
You can also greatly increase your chances of successful oxygen absorber storage by placing them into a vacuum chamber sealer. This removes the bulk or ALL of the oxygen while in storage and can be done with a jar or a bag.
At www.freezedryingsupplies.com we sell oxygen absorbers in packs of 10 to reduce the amount that needs to be stored and the potential for waste.
How do I know if my oxygen absorber packets are “good”?
So you just purchased a bunch of oxygen absorbers and you are ready to use them. Before you add these to your hard earned freeze dried food, make sure they are fresh and ready for use. Follow these tips for optimal results.
- A new packet of absorbers should be vacuum sealed (no exceptions).
- There should be a color indicator inside the packet. Before you open it, make sure the indicator is the correct color. For most, that would be pinkish/ red. If it is purple, they are no good. Also consider using this indicator if you are repackaging your unused absorbers. (for more info on this, go to “What do I do with extra oxygen absorbers?” section found above.
- A “good” or “fresh” oxygen absorber should feel pliable and the contents will feel loose similar to if it were filled with flour or powder. If it’s hard or crunchy, it's probably not any good.
**I always encourage you to do your own due diligence. This information is meant as a helpful guide.