“Gas barrier” isn't a single property

When talking about a packaging's gas barrier, it's worth specifying exactly which gas is being controlled. For coffee, oxygen and moisture are two especially important factors, but the ability to retain aroma compounds can also affect quality.

A film with a good oxygen barrier doesn't necessarily have an equally good moisture barrier. So no single figure can represent the entire protective effectiveness of a package.

Evaluating packaging needs to start from the actual risks the product faces and the intended shelf life.

Oxygen transmission rate shows how fast oxygen passes through the material

Oxygen transmission rate, usually abbreviated OTR, represents the amount of oxygen passing through a unit area of material over a given time under defined test conditions. This figure helps compare oxygen barrier between different material structures.

But OTR is a property of the material under specific measurement conditions. It doesn't automatically equal the actual amount of oxygen entering a complete coffee bag. The seal, lid, valve, temperature, and bag surface area can all change the real-world result.

So OTR is useful, but it needs to be read alongside the overall packaging design.

Water vapor transmission rate helps assess moisture barrier

Similar to OTR, water vapor transmission rate, usually abbreviated WVTR, describes the rate at which water vapor passes through a material under defined test conditions.

For coffee, this figure matters because moisture can change water activity, physical state, and the rate of quality decline. For ground coffee, moisture's effect can also show up as clumping and changes in brewing quality.

A packaging structure with low WVTR is beneficial when limiting moisture exchange is needed, but the seal and warehouse conditions still need to be considered.

Material specifications can't substitute for testing the complete package

Real packaging is a system made up of the film, the seal, a closure or lid, a valve, and the packing method. So beyond a material's OTR and WVTR, a production facility may need to assess seal integrity, seal strength, and the oxygen condition inside the finished package.

For roasted coffee, initial oxygen level and how the gas composition inside the bag changes are also worth attention, since CO2 keeps being released after roasting. A 2025 study on valved packaging found the gas environment inside the bag changes significantly with temperature and the degassing process.

So a good figure on a material's data sheet is only a starting point. The final question remains: does the whole packaging system protect the coffee under real conditions of use?

References

• ASTM / ISO packaging barrier test methods — Oxygen transmission rate and water vapor transmission rate
• Wiley — Storage Temperature Effect on Shelf Life Characteristics of Roasted Coffee Beans Packaged in Metalized Bag With a Pressure Releasing Valve (2025)
• Cardelli & Labuza — Application of Weibull Hazard Analysis to the Determination of the Shelf Life of Roasted and Ground Coffee (2001)