Have you ever noticed the rigid circular button-like object at the center of certain pouches and flexible bags? It’s called a one-way degassing valve, often used on fermented food and coffee packaging. Typically made out of high-density polyethylene (HDPE), the degassing valve’s purpose is to periodically allow gas to exit out from the inside of the package when the internal pressure exceeds a certain (small) value. As the name implies, air cannot flow from the outside inwards (because it’s a “one way” valve), resulting in an airtight seal to keep the internal contents fresh. How does it work? When the internal pressure is below a threshold value, the valve is shut to maintain an airtight seal. If the pressure of the internal contents exceeds a certain amount, however, the valve opens to allow for excess pressure to bleed off. By design air cannot enter the package through the valves even if the outside pressure is slightly greater than that of the inside. When is it needed...
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