Carbon dioxide (CO2) and coffee have a very interesting relationship. What makes it very interesting is that we want it around before we brew coffee, and as soon as we are ready to make a delicious cup, we want it ALL gone.
After we work our magic in the coffee roaster, the roasted coffee bean is ‘degassing,’ which means the CO2 that is formed from the roasting process is slowly leaking out of the structure of the bean. This is a good thing because if it is kept in a sealed bag with a one way valve (which Boss Batch Coffee is), then it will keep the oxygen away, and it will stay fresher for longer. The one way valve simply allows the gas to escape from the bag, so it doesn’t explode, but will not allow any air into the bag. This is why you want to keep your bag of coffee sealed until just before you are going to use it, because the moment you open the bag, the clock starts tickin’.
When brewing, though, the CO2 will prevent us from extracting all of the delicious flavors from the coffee. If you have ever seen water hit freshly ground coffee beans, you will notice that the coffee will bubble and ‘bloom,’ this is the CO2 leaving rapidly. This ‘blooming’ of coffee is very important because by saturating the ground coffee with water (usually about 2 times the weight of the coffee) and letting it sit for 30 to 45 seconds, it will allow the water to saturate the coffee and displace the CO2, leaving you with an unobstructed path to delicious coffee extraction. This is also a simplistic way to test the freshness of your coffee: if you get a great, full bloom, it is probably fresh, whereas if it is dull and flat, that would indicate there is not much CO2 present, and therefore probably stale. Also, the structure of dark roasted coffee is more porous than its lighter roasted counterparts, which means it will lose CO2 more rapidly, and thus, will stale more quickly.