One-way valve (degassing valve)

A small one-directional valve fitted to the front or side of a coffee bag, letting CO₂ escape from inside without letting oxygen in from outside.

Why it matters — Fresh coffee releases significant CO₂ in the days after roasting. Without a valve, the bag bursts; without a seal, the coffee stales rapidly. The valve solves both problems and is the reason specialty coffee can be packaged within hours of roasting.

Good to know

• Squeezing the bag near the valve and smelling lets you assess freshness at a glance — fresh coffee is loud and aromatic.
• Don't store coffee with the valve face-down — it makes the seal less effective over time.