What's that plastic knob on the Dunkin' Donuts coffee package?

by Ronda Lee
(Quad Cities, Illinois)

QUESTION:

Hi, I wonder if you could tell me what that plastic knob attached to the inside of my bag of Dunkin' Donuts coffee would be?

ANSWER:


It's a one-way valve. It allows air to get out of the package, but doesn't let any back in.

How come?

It doesn't let air in, because air is the enemy of coffee flavour. Air oxidizes the oils on the surface of the bean and steals its finer flavours.

But why does air need to get out?

It's all about freshness. To be as fresh as possible, coffee should be packaged as soon as possible after it is roasted. Ideally, it should be packaged immediately after roasting.

But there is a problem here. For some time after roasting, the still-warm coffee beans "gas off". In other words, they produce a small amount of gas. So if you put a few hundred hot beans in a bag and seal it...a little while later the bag will try to blow up like a balloon and will rip open. Big problem.

The valve allows these gases to escape from the bag while the beans cool. Problem solved.