For mason jars: no, you do not need an oxygen absorber if you vacuum seal the jar. Penn State Extension presents them as two ways to do the same job: put an oxygen absorber in the jar, or remove the air from the jar using a vacuum sealer. Pick one. Both remove oxygen from the container. For Mylar bags, the answer is different: the same source says an oxygen absorber is required.
That is the short version. The longer one explains why each method works, when using both makes sense, and what neither one can fix.
We sell vacuum sealers. Read this knowing that. Where this page makes a claim about food safety or storage, it links to the extension service that made it.
What each one actually does
An oxygen absorber and a vacuum sealer accomplish the same goal by different means: they reduce the oxygen inside a sealed container.
| Oxygen absorber | Vacuum sealer (mason jar) | |
|---|---|---|
| How it works | Iron powder inside the packet reacts with oxygen and holds it. The atmosphere inside the jar shifts from about 21% oxygen to nearly none. | Pulls air out of the jar mechanically before sealing. Removes air (and the oxygen in it) rather than binding it chemically. |
| When it acts | After the jar is sealed; continues working over hours or days | Immediately, before and during the seal cycle |
| Confirmation it worked | None you can see in the jar. Some absorbers change color. You have to trust the process. | The lid clicks down and stays down. Pressing the center confirms the seal. |
| Reusable | No. Single use. Remaining packets must be resealed immediately. | Yes. Open the jar, take what you need, seal it again. |
| Sizing | Must be sized to the container. Penn State says follow the manufacturer's directions. | No sizing; one machine, any jar size that fits |
| What extension says | For jars: an alternative to a vacuum seal. For Mylar: required. (Penn State) | For jars: an alternative to an O2 absorber. (Penn State) For Mylar: not named as an alternative. |
When does it make sense to use both?
Some freeze-dryer owners use both an oxygen absorber and a vacuum seal for foods where fat oxidation is the main risk over time. High-fat foods like meat, eggs, full-fat dairy, and nut-based meals go rancid when oxygen is present. A vacuum seal removes most of the oxygen immediately. Adding an absorber catches any residual oxygen the vacuum left behind.
For low-fat freeze-dried food like fruit, most vegetables, grains, and flour, most people use one or the other. If you vacuum seal in mason jars and you can see the lid is sealed, that is what Penn State Extension calls a valid approach.
Mylar bags: the absorber is required
For Mylar, Penn State Extension is specific: the bag must be used with an oxygen absorber and heat sealed. A vacuum seal on a Mylar bag is not named as a substitute the way it is for mason jars. Most freeze-dryer owners who use Mylar use both: vacuum seal the bag down to remove air, then the absorber handles the residual.
Our guide on Mylar chamber vacuum pouches covers the sealing process for bags.
Foods where absorbers are NOT recommended
Not every food belongs with an oxygen absorber. The freeze-dryer community and extension sources flag two categories.
- Sugar: will harden into a solid brick. Vacuum-sealed mason jars are the common approach for freeze-dried foods with very high sugar content.
- Salt: does not need an absorber and can cake.
When in doubt, ask in a freeze-dryer community about the specific food before sealing your whole batch.
What neither one can fix: moisture
An oxygen absorber and a vacuum sealer both address oxygen. Neither one fixes food that went into the jar damp. University of Minnesota Extension says freeze-dried foods absorb moisture easily, that even kitchen humidity can affect them, and that they should be packaged quickly in appropriate containers as soon as they come off the trays.
The dryness test: cut a piece of food in half and check for a dark spot in the middle. Dark means moisture, and all the trays go back in. Dryness comes first. Oxygen management comes second.
Sealing mason jars: which method to use
Penn State Extension points to three container types for freeze-dried food: glass canning jars, Mylar bags, and metal cans. For jars, the guidance is: an oxygen absorber or a vacuum seal. Here is how the common jar sealing methods compare.
- Handheld or hose jar sealer: one jar at a time, inexpensive. Good for a jar or two. Our step-by-step guide to vacuum sealing mason jars shows the process for each method.
- Chamber vacuum sealer with jar capacity: seals multiple jars per cycle. A home freeze dryer finishes all the trays at the same time, and one-jar-per-cycle tools mean twenty-four cycles for a full run. A chamber sealer designed to fit jars reduces that to four or five cycles. The JARMAX seals six pint jars or four quart jars per cycle, in a chamber 8.5 inches deep so the jars stand upright.
If you are also using Mylar for deep storage, the JARMAX has a 10.5-inch seal bar for Mylar up to 7 mil, so both tasks come off one machine. See how the JARMAX works or compare all the jar-sealing options in the best vacuum sealer for mason jars.
How to confirm the jar is sealed
Press the center of the lid. A sealed lid is pulled down and does not flex or click. If it clicks, the jar did not seal. Wipe the rim, check the lid for dents, and try again with a new flat lid if the second attempt also fails. This confirmation is something you can see and feel immediately, which an oxygen absorber alone does not give you.
From the community: oxygen absorbers and vacuum sealing
These are community members talking about chamber vacuum sealers in general. None of these people reviewed the JARMAX. The JARMAX is new. This is how people in the community talk about this category.
I use it to vacuum seal my freeze dried ingredients into Mason jars after they’re dried. I love that the container is reusable, unlike Mylar. If the freeze dried food is something meaty or with a little fat I’ll throw in an oxygen absorber too but I do like getting the air out before sealing it up.
Community discussion, r/Canning
I've used oxygen absorbers maybe once, but we really don't have high humidity here. Any jars for long term storage get vacuumed. Most of the food I dry get vacuum sealed in a chamber vacuum. So no oxygen absorbers for those, but that's mostly because they can puncture the bags.
Community discussion, r/HarvestRight
What freeze dryer owners told us
The JARMAX is new, so these are verified buyers of our other chamber sealers, in their own words. Each one says which machine they own.
Questions people ask
Do you need oxygen absorbers if you vacuum seal mason jars?
For mason jars, Penn State Extension says either put an oxygen absorber in the jar or remove the air with a vacuum sealer. A vacuum seal removes oxygen just as an absorber does. You do not need both for jars, though some people add an absorber for extra protection on high-fat foods like meat, eggs, or dairy. For Mylar bags, the same source says an oxygen absorber is required.
What does an oxygen absorber actually do?
An oxygen absorber is a small packet of iron powder that reacts with oxygen and holds it so the remaining gas inside the container is mostly nitrogen. It removes oxygen chemically, after the container is sealed. It is single use, needs to be sized to the container, and remaining packets have to be kept sealed to stay active.
What does a vacuum sealer do to oxygen?
A vacuum sealer pulls the air out of the container mechanically before sealing it. Because air is about 21 percent oxygen, removing the air removes most of the oxygen. A mason jar vacuum seal shows confirmation: the lid clicks down and stays down. You can open the jar and reseal it as many times as you need.
Which is better for freeze-dried food: oxygen absorbers or a vacuum sealer?
Penn State Extension treats them as equivalent options for mason jars. The practical differences: an oxygen absorber is a single-use packet that you add before closing and cannot reuse. A vacuum seal is mechanical, reusable, and shows you the seal worked. For Mylar, an absorber is required. For jars with high-fat food, some freeze-dryer owners use both.
Can you use oxygen absorbers and a vacuum sealer together?
Yes. Some freeze-dryer owners do both for foods where fat oxidation is a concern, like meat, eggs, and full-fat dairy products. The absorber handles any residual oxygen after the vacuum. For low-fat freeze-dried food like fruits, vegetables, and grains, one or the other is the common practice.
Do you need oxygen absorbers in Mylar bags if you vacuum seal them?
Penn State Extension says Mylar bags must be used with an oxygen absorber and heat sealed. A vacuum seal pulls air out but is not named as an alternative to the absorber for Mylar the way it is for mason jars. Most freeze-dryer owners who use Mylar use both.
Why should you not use oxygen absorbers with some foods?
Sugar will harden into a solid brick if sealed with an oxygen absorber. Salt does not need one and can cake. Some foods with very high sugar content are better in a vacuum-sealed jar than in Mylar with an absorber. Follow your freeze-dryer community's guidance for specific foods and always test before committing your whole batch.
How do you know if a mason jar vacuum seal worked?
Press the center of the lid. A sealed lid has been pulled down by the vacuum and will not flex or click when you press it. If the center pops up and down, the jar did not seal. Wipe the rim, check the lid for dents, and run the cycle again. A sealed lid is the confirmation you would never get from an absorber alone.
Keep reading
- How long does freeze-dried food last in mason jars vs Mylar?
- How to store freeze-dried food: mason jars, Mylar, and oxygen absorbers
- How to store freeze-dried eggs and other proteins long term
- Mylar bags vs mason jars for freeze-dried food: which and when
- How to vacuum seal mason jars: 3 methods, step by step
- The JARMAX: six jars a cycle, no hose
- Mylar chamber vacuum pouches for food storage
Sources
- Penn State Extension: Let's Preserve, Freeze-Drying (containers, O2 absorbers vs vacuum seal for jars, Mylar requirements)
- University of Minnesota Extension: Freeze-drying food (moisture pickup, packaging speed)
- University of Minnesota Extension: Vacuum sealing mason jars (vacuum sealing is not canning)
- National Center for Home Food Preservation: Packaging and storing dried foods
- Oregon State University Extension: Should I vacuum package food at home
Updated September 21, 2026. Reviewed by Eric at the Avid Armor workbench in Lenexa, Kansas.
