You roast a batch, pack it the same day, and three weeks later the customer says it tastes flat. Nothing went wrong in the roastery. The problem was in the bag.
Staling is mostly a film problem, not a storage problem. Once you understand what is attacking the product, choosing a pouch stops being guesswork.
What is actually happening
Four things shorten the life of roasted coffee and nuts:
- Oxygen. It reacts with the oils and turns them rancid. This is the main one.
- Moisture. The product takes on water from the air, and that speeds up the reaction above.
- Light. UV and visible light break down aromatic compounds.
- Heat. Every 10 °C rise roughly doubles the speed of these reactions.
You cannot control the last one once the bag leaves your hands. You can control the first three, and that is what packaging is for.
Barrier is measured, not guessed
Two numbers tell you how protective a film is:
- OTR — oxygen transmission rate. How much oxygen passes through a square metre of film in a day. Lower is better.
- WVTR — water vapour transmission rate. The same idea, for moisture.
You do not need to memorise the figures. You just need to know that a foil laminate has an OTR hundreds of times lower than plain PE film, and that this is the difference between coffee that holds for a year and coffee that fades in a month.
Common structures and what they block
| Structure | Barrier | Typical use |
|---|---|---|
| PE only | Poor | Bread bags, produce. Not for coffee. |
| PET / PE | Moderate | Dried goods, short shelf life |
| PET / metallised PET / PE | Good | The standard coffee bag |
| PET / foil / PE | Very good | Long shelf life, premium coffee |
| PET / foil / nylon / PE | Very good, plus strength | Vacuum packs, sharp edges, rough handling |
More layers is not automatically better. Each one adds cost and thickness. The right question is how long the product has to hold, and the answer decides the structure.
Foil or metallised?
This one comes up constantly.
Metallised film has a thin layer of aluminium vapour deposited onto a plastic film. It reflects light and slows oxygen, and it costs less than foil.
Foil is a solid sheet of aluminium. It is an absolute barrier — very little diffuses through it — and it blocks light completely.
For most coffee sold and drunk within a few months, a good metallised structure is enough. For coffee that has to sit on a shelf for a year, or travel by sea, foil earns its cost. If you are selling single-origin beans at a premium, the difference in a side-by-side tasting after six months is not subtle.
The one-way valve
Freshly roasted coffee releases carbon dioxide for days. In a sealed bag that gas has nowhere to go, so the bag inflates and the seams come under pressure.
A degassing valve lets the gas out and keeps air from coming back in. It is a small part, but for roasted coffee it is not optional. Skip it and you risk seam failures and a bag that feels like a balloon on the shelf.
How long can you expect?
Rough expectations, properly sealed and stored, without opening the bag:
| Structure | Realistic shelf life for roasted coffee |
|---|---|
| PET / PE | Weeks. Not suitable for retail. |
| Metallised, valved | 3 – 6 months |
| Foil, valved | 9 – 12 months, sometimes more |
Once the bag is opened, all of this resets. Air gets in every time the zipper opens, and most coffee is at its best within a few weeks of opening. That is worth printing on the back of the bag — it sets expectations and it is honest.
The short version
- Oxygen, moisture and light do the damage. Block them and you buy time.
- Metallised is fine for short shelf life; foil is for the long haul.
- Roasted coffee needs a valve.
- Match the film to the shelf life you actually need, not to the most expensive option on the list.
Tell us what you are packing and how long it has to last, and we will suggest a structure and a price for it. You can see the barrier films we run on our aluminum foil roll stock and coffee packaging pages.
