Mylar Bags and Oxygen Absorbers for Dried Herb Storage

For dried culinary herbs, pair a foil-layer barrier bag with food-grade oxygen absorbers rated for the volume of air left in the bag, then seal it fully. The absorber rating comes from the maker's packet or chart, so this guide gives no ratio of its own. It shows how to size by volume, which features to look for in the bag and where people go wrong.

Everything below is equipment guidance for dried herbs and similar dry goods. The two extension pages cited at the end are the basis for the storage points, and the absorber maker's instructions beat any rule of thumb you read online.

Why the pairing matters

A barrier bag slows the movement of oxygen and moisture through the wall. An oxygen absorber removes the oxygen already inside. Using only one of them leaves a gap. Utah State University Extension describes foil laminate pouches as having a food-grade PET inner layer and a foil layer that dramatically reduces the transmission of oxygen and moisture, and it says oxygen absorbers should be used for spices and seasonings and for dried beans and milk to extend shelf life. It also notes that dried foods must be sealed to keep them from taking up moisture from the air.

The same page makes a point that applies to every bag in this guide: rodents can chew through these pouches, even with the metal layer. If you store dried herbs in a shed or packing room, put the sealed bags in a lidded tote or a rodent-resistant container rather than leaving them on a shelf. The stackable food-safe tote guide covers lids and stacking.

Choosing the bag

"Mylar" is a trade name that people use for any shiny barrier bag. USU says as much. What you are buying is a foil laminate pouch, so read the listing for what it actually is.

Size the bag to the product. A bag that is mostly empty holds more air than it needs to and calls for a larger absorber, and a bag stuffed to the top is hard to seal. Fill to a level that leaves enough film to seal across cleanly.

Reading an oxygen absorber label

Absorber packets are rated by how much oxygen they can remove, and the packet or the seller's chart tells you how to match that rating to a container. This guide quotes no number, because USU's packaging page does not give a sizing rule and a made-up ratio is worse than none. Use the maker's chart for the packet you buy, and match it to the air volume in the sealed bag, not the weight of the herbs.

• Volume of air: bag capacity minus the space the herbs take up. A loosely packed bag of fluffy herb leaves holds a lot of air.
• Food-grade wording: USU recommends food-safe absorbers from food storage suppliers. Check the packet says it is for food use.
• Count and pack size: absorbers come in sealed packs of many. Do not buy a bulk pack for a job that needs two.
• Date and storage: check for a packing date or expiry on the pack if the maker gives one, and store unused packets as the maker says.

Handling the packets

Absorbers start working once exposed to air, so the usual advice is to prepare everything first. Have the bags filled, the sealer warm and the label ready, then open the pack and pull out only what you need. Reseal the rest immediately in an airtight container, as the maker directs. Work quickly and do not leave packets sitting on the bench.

Moisture comes first

An absorber does not make wet product safe. Ask Extension's answer on the subject says food-grade absorbers are only recommended for properly dried foods, and notes that absorbers use water in their reaction so they pull moisture from the air or the food, which affects low-moisture foods most. USU adds that dried foods should be cooled and conditioned completely before packing, because packing warm food can cause sweating and mold.

NCHFP's herb page gives a simple readiness check for dried herbs: leaves should be crispy dry and crumple easily between the fingers before packaging. Use that before you sacrifice a bag and an absorber on a batch that is not ready. If you dry your own, the dehydrator versus air drying comparison and the herb bundling supplies guide cover the earlier steps.

Sealing the bag

USU says bags can be heat-sealed or closed with twist ties, string or rubber bands. For a foil bag with an absorber, a heat seal is the better choice because it closes the whole width of the bag. A zip or twist closure is fine for temporary storage but is not a full oxygen barrier.

• Press out excess air by hand without crushing the contents, then seal in one pass.
• Check the seal line is flat and even across the whole width. Re-seal if it looks wavy or partial.
• Leave a little tail above the seal so you can cut and reseal the bag once or twice.
• Label the bag with the contents and date. A paper label inside a clear sleeve survives cold storage better than ink on foil.

An impulse sealer is the usual tool. The impulse sealer guide covers sealing width, cool-down time and what to look for in a small-farm unit. Heat sealers are heated equipment, so follow the manual.

Where the pairing goes wrong

• Using absorbers on product that is still damp, or packing warm product straight from the dryer.
• Buying an absorber for the size of the bag name rather than its internal volume.
• Leaving the pack of absorbers open between jobs.
• Skipping the lidded tote and giving rodents a chance at the bags.
• Treating a bag with a zip top as sealed.

If you also store herbs in jars or rigid containers, the same rules about dryness apply. Where you keep the bags matters too: NCHFP says dried herbs belong in a cool, dry, dark place, and a hygrometer is the quickest way to see whether your storage room is dry; see the hygrometer guide.

Frequently asked questions

Sources and verification