Why do coffee bags have valves?

// Guide · Coffee Valves

That little round button on a bag of specialty coffee isn’t there for you to sniff, though most of us do. It’s a one-way degassing valve, and it’s the single feature that lets a roaster bag coffee fresh off the roaster without the pack bloating, bursting or going stale.

This guide explains what the valve is called, why freshly roasted coffee releases CO₂, exactly how a one-way valve works, internal valves versus the “valve sticker” look, when you actually need one (and when you can skip it), what happens to the valve at end of life, and how it affects shelf life across the different bag formats.

// The Short Answer

What is the valve on a coffee bag?

Freshly roasted coffee is not inert. For days after it leaves the roaster, it releases carbon dioxide, a natural process called degassing. Seal those beans in an airtight bag with nowhere for the gas to go and the pack inflates like a balloon, and eventually splits at the seams.

A one-way degassing valve solves the problem elegantly: it lets CO₂ out while stopping oxygen from getting in. That single piece of engineering is what makes it possible to roast, bag and seal coffee the same day, keep it fresh for months, and ship it without a single burst pack.

What it’s called: the correct name is a one-way degassing valve. You’ll also see it called a coffee valve, a freshness valve, a coffee bag valve or, because of how it looks on the outside of the pack, a valve sticker. Wicovalve is the brand of one-way degassing valve used on our bags.

The nose test we all do at the shop shelf is a happy side effect, but the valve earns its place for a far more practical reason.

// The Science

Why freshly roasted coffee degasses

When green beans hit the heat of the roaster, the sugars and amino acids inside them react and transform: the chemistry behind coffee’s colour, aroma and flavour. A by-product of that reaction is a large volume of carbon dioxide, most of which stays trapped inside the porous structure of the bean after roasting.

That trapped gas then works its way out over time. Degassing is at its most vigorous in the first hours and days after roasting and tapers off over the following couple of weeks. The fresher the roast, the more gas it gives off, which is why the problem is most acute for exactly the coffee people want most: coffee bagged soon after roasting.

There’s a second, opposite problem. Oxygen stales coffee. Oxidation strips out aromatics and dulls flavour, so the last thing you want is fresh air circulating inside the pack. The roaster is caught between two needs: let gas escape, but keep oxygen out. A plain sealed bag can’t do both. A valved bag can.

// How It Works

How a one-way degassing valve works

The mechanism is simple, and that’s the beauty of it. A one-way valve is a small self-regulating pressure-relief device fitted to the bag film.

1. Pressure builds inside. As the beans degas, CO₂ collects in the headspace and pressure rises inside the sealed bag.
2. The valve opens outward. Once internal pressure passes a set threshold, it pushes the valve’s seal open and vents the excess gas to the outside.
3. It reseals and stays shut to air. When pressure drops back, the seal closes again. Crucially, outside air can’t push its way in the other direction, so oxygen stays out.

The net effect: gas escapes, the bag holds its shape, and the coffee sits in a low-oxygen environment while it finishes degassing. Our coffee bags use a proven one-way Wicovalve degassing valve.

// Types, Placement & Valve Stickers

Internal valves, external valves and the “valve sticker”

Degassing valves come in two mounting styles. Both do the same one-way job; the difference is where the valve body sits and how it looks on the finished bag.

What about coffee bags with valve stickers? On the outside of the pack, a degassing valve looks like a small round sticker, which is why many people search for a “valve sticker” or a “coffee package valve sticker”. It isn’t a label: the small round vent is where the gas escapes, and the one-way mechanism behind it is what keeps oxygen out. If you add your own labels to stock bags, keep them clear of the valve so the vent isn’t covered.

Placement matters too. The valve is normally positioned on the upper front or back panel of the bag, above the fill line, so it vents into headspace rather than being clogged by coffee. On a box bottom or side gusset bag it usually sits high on a front face; on a stand up pouch, near the top of a panel.

If you buy stock bags from us, the valve is already fitted and positioned correctly. We also sell Wicovalve degassing valves on their own (Type W006 and Type W606, in boxes of 10,000) for roasters who apply their own valves to film.

// When You Need One

When you need a valve, and when you don’t

A valve is essential whenever you’re packing coffee that is still actively giving off gas. It’s unnecessary, and an added cost, for products that aren’t.

Use a valve for:

• Whole bean or ground coffee bagged soon after roasting: the classic case.
• Any freshly roasted specialty coffee where you want to seal quickly and protect aroma.

You can usually skip it for:

• Coffee that has been rested and fully degassed before bagging.
• Instant coffee, which doesn’t degas.
• Single-serve drip coffee bags, and non-coffee products such as tea, granola or pet food.

This is why we stock coffee bags both with and without a valve, so you only pay for one when your product needs it.

// End of Life

What happens to the valve when the bag is recycled or composted?

The valve is a separate component from the bag film, so it matters which bag it’s fitted to.

• Recyclable mono-PE bags: our recyclable bag uses an LDPE valve and an LDPE zip, so the whole bag, valve included, is recyclable in the PE film stream where collection exists.
• Compostable bags: degassing valves are industrially compostable only. If the bag is going into a home compost, remove the valve first.

Sorting rules for packaging differ from country to country across Europe. Our guide to how to recycle different types of coffee packaging covers where each bag type goes, and our PPWR guide explains what the EU’s packaging regulation means for coffee bags.

// Shelf Life

How the valve affects shelf life

A valve doesn’t work alone. Shelf life is the product of two things working together: the barrier of the film (how well it keeps oxygen, light and moisture out) and the valve (how it manages the gas the coffee itself produces).

Pair a high-barrier film with a one-way valve and you get the best of both: the coffee can be sealed fresh, the CO₂ it releases vents safely, and very little oxygen ever reaches the beans. A high-barrier bag with no valve risks bloating; a valve on a low-barrier film still lets staling oxygen creep in over time.

Typical: roasted coffee, unopened, in a valved bag, stored cool and dry. Maximum: the barrier structure under ideal storage; it is not a guarantee.

Barrier and end of life are a trade-off worth understanding: foil laminates give the longest shelf life, while mono-material recyclable and compostable films are kinder at end of life with a shorter shelf life. We cover every film structure in our materials guide.

// Formats

Valves across the different bag formats

A degassing valve can be fitted to any of our coffee formats. The valve does the same job regardless of shape; each format simply gives it a different home.

• Box bottom bags: the premium retail standard; the valve sits high on the large front panel.
• Side gusset bags: the traditional silhouette for bulk and wholesale, valve on a front face, often paired with a tin tie.
• Stand up pouches: versatile and resealable; valve near the top of a panel.
• Flat pouches and drip coffee bags: sample and single-serve formats that typically don’t need a valve, as the coffee is either a small taster or already portioned for immediate brewing.

Want your own branding on a valved bag? Custom print starts at 2,000 units with about 11–12 weeks from order to delivery: we supply the dieline, set your artwork on it and proof digitally before production. Get a quote to start.

New to choosing coffee packaging? Start with our coffee packaging beginner’s guide, which walks through formats, sizes, materials and the stock-vs-custom decision.

// FAQ

Frequently asked questions

Why do coffee bags have a valve?

Freshly roasted coffee releases carbon dioxide for days after roasting. A one-way degassing valve lets that CO₂ escape so the sealed bag doesn’t inflate or burst, while stopping oxygen from getting in and staling the coffee.

What is the valve on a coffee bag called?

Its proper name is a one-way degassing valve. It’s also called a coffee valve, a freshness valve or a valve sticker, because from the outside it looks like a small round sticker. Wicovalve is the brand of degassing valve used on our coffee bags.

How does a one-way coffee valve work?

As gas builds up inside the bag, internal pressure opens the valve and vents CO₂ to the outside. When the pressure drops the valve reseals, and because it only opens outward, outside air can’t flow back in, so oxygen stays out.

Do all coffee bags need a valve?

No. A valve is needed for coffee bagged soon after roasting while it’s still degassing. Fully rested coffee, instant coffee, single-serve drip bags and non-coffee products such as tea or granola generally don’t need one. We stock coffee bags both with and without a valve.

Do I need to remove the valve before recycling or composting?

It depends on the bag. Our recyclable mono-PE bag uses an LDPE valve and LDPE zip, so the whole bag is recyclable in the PE film stream where collection exists. On compostable bags, the degassing valve is industrially compostable only, so remove it before home composting.

Can I buy just the valves?

Yes. Alongside coffee bags with valves already fitted, we sell Wicovalve one-way degassing valves separately, in boxes of 10,000, for roasters who apply their own. Browse our valves.