The oxygen math, in three steps
- Container volume. A gallon is 3,785 cc. A quart is 946 cc.
- Oxygen in that air. Air is about 21% oxygen, so a sealed empty gallon holds about 795 cc of oxygen.
- Air left around the food. Food takes up some of the space. Dense food like rice or powder leaves maybe 38% air. Loose freeze-dried pieces leave about 60%, and airy foods like puffed candy and whole berries closer to 80%. Multiply, then round up to a packet size.
An absorber’s cc rating is the oxygen it can remove, so a 500 cc packet handles the 500 cc of oxygen in a loosely filled gallon bag.
Quick chart
| Container | Dense | Loose freeze-dried pieces | Very airy |
|---|---|---|---|
| Pint jar (16 fl oz) | 50 cc | 100 cc | 100 cc |
| Quart jar or quart bag | 100 cc | 300 cc | 300 cc |
| Half-gallon jar or bag | 300 cc | 300 cc | 500 cc |
| 1 gallon mylar bag | 300 cc | 500 cc | 750 cc |
| 2 gallon mylar bag | 750 cc | 1000 cc | 2000 cc |
| #10 can (about 3 L) | 300 cc | 500 cc | 750 cc |
| 5 gallon bag or bucket | 2000 cc | 2500 cc | 2500 + 750 cc |
Numbers without extra margin. Packet sizes used: 50, 100, 300, 500, 750, 1,000, 2,000 and 2,500 cc.
Packaging that makes absorbers work
- The food must be fully dry. Absorbers are for dry food only; use the dryness check first.
- The bag must block oxygen. Iowa State Extension notes mylar bags with a clear window are not airtight long term. Use foil mylar, glass jars or #10 cans.
- Seal with heat. An impulse or iron sealer across the full width. Zip tops alone leak slowly.
- Store cool and dark. Heat speeds up every kind of quality loss, especially in fatty foods.
- Replace the absorber when you reopen. Once used up, it cannot protect the bag a second time.
Read next
- Making Your Own Freeze-Dried Backpacking Meals: Which home meals freeze-dry and rehydrate well on the trail, how to portion and pack them, how much water each needs, and the fat and safety limits to respect.
- How Long Does Home Freeze-Dried Food Last? The 25-Year Claim, Checked: Where the 25-year number comes from, why Utah State Extension recommends eating home freeze-dried food within 5 to 10 years, and what actually shortens shelf life.
- Mylar Bags and Oxygen Absorbers for Freeze-Dried Food: Which bag thickness to buy, how many cc of oxygen absorber each bag size needs, how to seal properly, and the packing mistakes that ruin a batch months later.
Questions people ask
What size oxygen absorber for a 1 gallon mylar bag of freeze-dried food?
About 500 cc. A gallon is 3,785 cc and air is about 21% oxygen, so an empty gallon holds roughly 795 cc of oxygen. Loose freeze-dried pieces leave around 60% of the space as air, which works out near 500 cc. Discount Mylar Bags gives the same rule: 300 cc for dense food, 500 cc for bulky or freeze-dried food.
Can I use too many oxygen absorbers?
No. Extra capacity simply goes unused. Too little is the common mistake, so round up.
Oxygen absorber or desiccant?
They do different jobs: absorbers remove oxygen, desiccants remove moisture. Iowa State Extension says an oxygen absorber, not a desiccant, belongs in freeze-dried food storage. Some packers add both for very hygroscopic foods like powders and candy.
How do I keep unused absorbers good?
They start working as soon as they meet air. Open a pack only when bags are filled and ready to seal, and put the rest back into a small jar or sealed bag within minutes.
Should the bag shrink after sealing?
Often, yes. As the oxygen is absorbed the bag pulls in around the food, sometimes called printing. Airy freeze-dried food and powders may not print visibly; a bag that puffs up over time is the warning sign.
Sources
- Discount Mylar Bags: Technical reference guide, oxygen absorbers (formula and 300 / 500 cc rule)
- Iowa State University Extension AnswerLine: absorber not desiccant, larger is fine
- Utah State University Extension: Can I Freeze-Dry That? (packaging)
Figures checked 2026-10-21. How we check them. Spot something off for your machine? Tell us.