One-way degassing valve

A one-way degassing valve is a small fitment sealed into a pouch that lets gas out but stops outside air, and therefore oxygen, from getting in. It is a standard feature on bags of freshly roasted coffee.

Why coffee needs it

Roasted beans keep releasing carbon dioxide for days after roasting. Seal them in an airtight pouch straight away and the bag balloons; wait until degassing ends and aroma is lost to oxidation. The valve lets roasters pack coffee fresh while the gas escapes.

How it works

A typical valve has a plastic body, a flexible membrane and a thin film of liquid, often silicone oil, that keeps the membrane sealed. When internal pressure rises the membrane lifts and gas vents; when pressure drops it closes again. The valve is welded to the inside of the front panel over small perforations.

Design points

• Place it in the upper part of the front panel, above the product level, and plan it with the artwork.
• Its sealing face must suit the pouch's inner layer.
• The pouch itself must be high barrier, usually foil or metallised, otherwise the valve is pointless.
• For mono-material packs, check that the valve material is compatible.

The valve helps, but shelf life also depends on roast date, grind, nitrogen flushing and the laminate's oxygen transmission rate.