How long do oxygen absorbers last once opened?

Quick Answer

Oxygen absorbers typically last only a few hours once the packaging is opened and exposed to air. However, if re-sealed tightly in an airtight container, they may last up to 1-2 days.

What are Oxygen Absorbers?

Oxygen absorbers, also known as oxygen scavengers, are small packets containing iron powder that absorbs oxygen from the surrounding environment. They are commonly used when packing foods, pharmaceuticals, or other oxygen-sensitive items to help remove oxygen from inside the packaging. This helps extend the shelf life and avoid spoilage.

How Do Oxygen Absorbers Work?

The iron powder inside oxygen absorbers reacts with oxygen in the following chemical reaction:

4Fe + 3O2 → 2Fe2O3

In this reaction, iron (Fe) binds with oxygen (O2) to form iron oxide (Fe2O3), also known as rust. As more oxygen is absorbed by the iron, the iron eventually turns completely to iron oxide, its maximum absorption capacity.

At this point, the oxygen absorber is spent and can no longer absorb any more oxygen. The oxygen absorption process generates heat, so spent oxygen absorbers will feel warm to the touch.

Benefits of Using Oxygen Absorbers

There are several key benefits to using oxygen absorbers in packaging:

– Removes oxygen from packaging to extend shelf life of contents
– Inhibits growth of aerobic bacteria, molds, and fungi
– Prevents oxidation reactions that can degrade food quality
– Allows vacuum packaging without need for vacuum machine
– Environmentally friendly and safe for contact with food

By removing oxygen, oxygen absorbers can extend the shelf life of packaged foods and other products significantly.

How Long Do Oxygen Absorbers Last Once Opened?

Once the packaging around oxygen absorbers is opened and exposed to air, the oxygen absorption process begins. The precise timing will depend on factors like:

– Size of oxygen absorber – Larger packets absorb more oxygen
– Exposure to air – More exposure accelerates absorption
– Humidity – Higher humidity speeds up absorption

Typical Lifespan When Opened

Under average conditions, most oxygen absorbers have a functional lifespan of just a few hours once opened before becoming saturated.

Small, 1g oxygen absorbers may only last about 3-4 hours once exposed to air. Large, 5g oxygen absorbers may absorb for up to 8-12 hours when opened.

If the packaging around the oxygen absorber is opened briefly and then re-sealed tightly, the lifespan may be slightly longer. But overall, oxygen absorbers lose effectiveness rapidly after exposure to oxygen.

Extending Lifespan in Airtight Containers

It is possible to extend the usable lifespan of oxygen absorbers once opened by putting them into an airtight glass jar or Mylar bag and sealing tightly.

This limits oxygen exposure so that the absorption process is slowed. In a very well-sealed container, some oxygen absorbers may last up to 1-2 days before becoming saturated.

Proper storage conditions are important for maximizing length of time the absorbers remain usable:

– Store in small, airtight containers
– Use packaging with minimal headspace
– Remove as much air as possible before sealing
– Use an oxygen indicator to monitor oxygen levels

With optimized storage, oxygen absorbers can remain partially effective for up to 48 hours. However, their capacity quickly declines once exposed to air.

Signs Your Oxygen Absorbers are Spent

Here are some signs that your opened oxygen absorbers have reached full absorption capacity and are no longer usable:

– Warm to the touch – The iron oxidation reaction generates heat
– Change from gray to brown or black – Iron turned to iron oxide
– Brittle texture – Oxygen absorbers become dried out
– No vacuum achieved in packaging – Oxygen still present
– Oxygen indicator shows presence of oxygen

Once oxygen absorbers show these signs, they should be discarded and replaced with fresh absorbers for effective oxygen absorption.

Testing Oxygen Levels

For the most accurate way to test whether an opened oxygen absorber is still functional, use an oxygen indicator inside the packaging.

Oxygen indicators contain a reactive dye that changes color in the presence of oxygen. Some common types are:

– Iron powder indicator – Changes from pink to brown/black
– Methylene blue indicator – Changes from blue to colorless

If the indicator color change occurs, it means oxygen levels are still above the desired threshold and the oxygen absorber is expired.

Frequently Asked Questions

Can you reuse an opened oxygen absorber?

Once an oxygen absorber is opened and exposed to air, it cannot be reused. The iron powder will already have reacted with oxygen and turned to iron oxide. Used oxygen absorbers should be discarded and replaced with new, unused absorbers.

How can you seal an opened oxygen absorber for storage?

For temporary storage of opened oxygen absorbers, seal them tightly in glass jars, Mylar bags, or vacuum packaging to limit oxygen exposure and slow absorption. Remove as much air as possible before sealing and use oxygen indicators to monitor oxygen levels.

Do humidity packs extend oxygen absorber life?

Yes, moisture accelerates the oxygen absorption process. Storing opened oxygen absorbers with desiccant packs that maintain low humidity will help extend their usable lifespan by slowing down absorption.

Can opened oxygen absorbers be reactivated?

Unfortunately, once oxygen absorbers are saturated, there is no way to reactivate them. The iron powder has chemically changed to iron oxide through oxidation and cannot be reversed. The absorbers must be discarded and replaced when spent.

Is it safe to use an opened oxygen absorber?

Oxygen absorbers are generally safe to use even after opening, as long as they still have absorption capacity left. However, once fully spent, they should not continue to be used, as they will no longer absorb oxygen.

Storing Unused Oxygen Absorbers

To get the longest shelf life out of unused, unopened oxygen absorbers, proper storage is important:

– Keep in original packaging until ready to use
– Store in cool, dry place away from direct sunlight
– Avoid high temperatures and moisture
– Use before expiration date printed on packaging
– Seal packaging tightly between uses to avoid air exposure

With ideal storage conditions, unopened oxygen absorbers typically last around 6-24 months from the date of manufacture. Check packaging for the recommended shelf life.

Properly stored oxygen absorbers should retain full absorption capacity until you are ready to open and use them. Once exposed to air, their lifespan becomes very limited.


Oxygen absorbers begin losing effectiveness immediately after opening and have a functional lifespan of just a few hours when exposed to air. With optimized re-sealing and storage, they may last up to 1-2 days. Signs like warmth, color change, lack of vacuum, and oxygen indicator results will let you know if absorbers are no longer usable.

For best results, oxygen absorbers should only be opened when you are ready to use them for packaging. Store unused absorbers properly to maximize shelf life. And replace spent absorbers promptly for continuing protection of oxygen-sensitive contents.

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