Oxygen absorbers are small, porous sachets included in sealed packaging to protect contents from degradation. Their primary function is to remove gaseous oxygen from the air inside a container, which significantly extends the shelf life of food and preserves the quality of other sensitive items. This preservation stops chemical and biological processes that rely on oxygen, such as oxidation and the growth of aerobic microorganisms. Without an oxygen absorber, the residual air trapped in a container (roughly 21% oxygen) can quickly lead to spoilage.
Core Components and Mechanism
The contents of a standard oxygen absorber sachet consist mainly of finely powdered iron, sodium chloride (common salt), and sometimes a small amount of activated carbon. The iron powder is the active ingredient responsible for scavenging the oxygen from the surrounding atmosphere. This powder is engineered to have a large surface area, which allows the chemical reaction to occur efficiently and quickly.
The mechanism by which the absorber works is essentially a controlled form of rusting, known as oxidation. When the sachet is exposed to moisture inside the sealed container, the iron reacts with the oxygen to form iron oxide, which is rust. This chemical conversion permanently binds the oxygen molecules, effectively removing them from the container’s free air space.
Sodium chloride plays a role in accelerating this oxidation process by acting as an electrolyte. The presence of salt allows the iron to react with oxygen even in environments with low humidity, which is common in dry food storage. Activated carbon is often included to absorb trace gases and odors, further improving the preservation environment. When correctly used in an airtight container, these sachets can reduce the oxygen level to less than 0.01% of the atmosphere.
Practical Application and Selection
Oxygen absorbers are used for long-term food storage, particularly for dried goods like grains, beans, dehydrated fruits, and powdered milk. By eliminating oxygen, they prevent the rancidity of fats, stop color and flavor changes, and inhibit the development of mold, yeast, and insects. They are most effective when paired with packaging materials that have a low oxygen transmission rate, such as Mylar bags or glass jars with tightly sealed lids.
Absorbers are rated by their capacity in cubic centimeters (cc), which indicates the maximum volume of oxygen they can absorb. Common sizes range from 50cc for small containers to 2000cc for bulk storage. For instance, a 100cc absorber is typically sufficient for a quart-sized jar or bag, while a 2000cc absorber is often needed for a 5-gallon bucket.
Selecting the correct size is based on the container’s volume and the amount of air space, or headspace, present after the food is added. Absorber capacity should be slightly oversized to account for residual oxygen trapped within the food, particularly with porous items like pasta or freeze-dried meals. Once the original vacuum-sealed package is opened, the packets must be used quickly, typically within 15 to 30 minutes, before they react with ambient air and are fully spent.
Safety Profile and Handling
The ingredients inside the sachet are considered non-toxic, as they are primarily food-grade iron powder and salt. The iron oxide end-product is chemically inert, meaning it poses no risk to the stored food. Because of this, the packets are safe for incidental contact with food items.
Oxygen absorbers are clearly labeled “Do Not Eat” for several reasons. The packet itself presents a physical choking hazard, especially to children and pets. While the ingredients are not toxic in small amounts, consuming a large number of packets could lead to iron poisoning, a serious medical concern.
Once an absorber has been fully spent, it becomes a hard, solid block of rust and can be disposed of with regular household waste. If packets feel hard before use, it indicates they have already reacted with oxygen due to extended air exposure and should be discarded. Unused absorbers should be stored immediately in a small, airtight container to preserve their effectiveness for future use.