Degassing occurs because when coffee is roasted, carbon dioxide forms inside the bean. Much of that gas is released in the first few days after roasting.
Carbon dioxide surrounds the ground coffee particles, thus forming a ‘bubble’ that prevents water from penetrating and properly extracting soluble compounds. For this reason, freshly roasted coffee should be left to rest for a number of days until all the best flavors can be extracted.
The degassing period can last up to 20 days. The length varies according to the botanical species (for example Robusta retains more gases than Arabica), the type of roast, variation in the size of the beans and their humidity, as well as the packaging and whether or not it contains a valve to let the gases out.
Another factor is whether the bean is whole or ground; the former takes longer to degas, since the emission of gases is greater in the smaller particles of ground coffee.
Degassing must be carried out in a precise and controlled manner, since the gases contain the aromas you can find in the cup. The more a coffee is degassed, the more aromas it will lose; on the other hand, if few gases are released, the coffee risks becoming rancid faster.
To consume coffee beans at their peak and ensure a good extraction, the roasting date and other factors such as storage, temperature, and humidity must be taken into account.
Poorly degassed coffee will affect how well the beans can be ground and lengthen the extraction process, since the gases will prevent water from reaching the soluble compounds, which will result in a poor quality drink.