Why Do Coffee Bags have a Valve? The Off-Gassing of Coffee
You'll notice that our coffee bags have a one way valve. This is to allow for a process called off-gassing.
When coffee is roasted, chemical reactions create gases (mostly CO2.) Some of this gas is released during the actual roasting process, but over the next 48 hours it continues to be released from the porous bean structure, particularly when you grind your fresh beans.
The release of gas during each stage is actually a very important event.
It indicates a freshly roasted batch and plays a large role in the taste, helps to form the 'crema' and influences the taste / profile of the cup.
Typically we allow our beans to off-gas in special bins after roasting, after which they are sealed in bags with a one-way valve to allow the process to continue without gas pressure becoming too high in the bag.
(( Personally, we feel the one-way valve is has an equally important role in smelling coffee - there is nothing better than squeezing a freshly roasted bag and taking in the smell and gas released through the valve!))
If roasted beans go straight to bag for delivery immediately, we'll let you know how long to allow your beans to off-gas.