CO2 and Oxidation
Generally speaking, fresh coffee is better than old coffee – but that's only part of the truth.
After roasting, coffee contains a lot of CO2, which escapes slowly throughout the following weeks. This is also the reason for the valve on the coffee bag (it's not there so you can smell the coffee): CO2 can leave the bag, which won't inflate, and oxygen won't get into the bag, which prevents a quick oxidation.
Back to freshness. If you drink coffee right after roasting, it contains too much CO2 and this will affect your extraction, so you want to avoid super-fresh coffee, especially so when using an espresso machine (as opposed to, say, a v60 pour over brew).
2-3 Weeks After Roasting
Most coffees taste the best two to three weeks after roasting. This applies to both espresso and filter roasts. For filter coffee, this is definitely less crucial. The extraction can turn our really great even with really fresh coffee, the aroma and flavor do usually improve within the next 2-3 weeks.
After those 2-3 weeks, the coffee does not just turn bad instantly, but it loses aroma gradually from week to week. Even after a couple of months, coffee can be consumed without any problems and it can still taste great. If you use pre-ground coffee, freshness is lost much more quickly, which is why it's best to grind coffee right before brewing.
Is Too Fresh Really Bad?
While filter coffees can be drunk as soon as a day after roasting without any problems and taste great, we recommend to wait around two weeks before brewing fresh coffee on an espresso machine (if possible, of course). Your espresso extraction will most likely be influenced strongly by the CO2 and your espresso might be both under- and overextracted at the same time (google «espresso channeling» to find out more about the topic).
There are ways to improve your results with really fresh coffee, like letting your coffee sit for perhaps 15 minutes after grinding before you use it in your espresso machine. This speeds up degassing of the coffee, but it's obviously not ideal and not very practical.
The Best Way to Store Coffee
So the CO2 and other gases can escape from the coffee bean, most packages are equipped with a one-way pressure valve. Due to this, air does not get inside, but gases can leave the bag. Thus, the bag does not inflate like a balloon when gases are released from the coffee. Therefore, ideally, coffee is stored in the original bag it was in at the time of purchase (as long as this is an airtight bag with pressure valve). To store coffee beans which are a few days or weeks old and have thus released most of the gases already for a little longer than 2-3 weeks, vacuum containers such as the Fellow Atmos are a great solution. This kind of container creates a vacuum to protect the coffee from oxidation, thus prolonging its lifespan. This is especially useful for slightly older coffee, which is not intended for immediate preparation.
- coffee usually reaches its full potential 2-3 weeks after roasting
- avoid drinking espresso roasts within the first two weeks after roasting if possible – plan ahead when buying
- try your filter roasts sooner after roasting to find out how the aroma and flavor change over time
- shelf life is usually at the very least six months, for most coffees much more
- when it comes to aroma and flavor, better drink up the coffee within 2-3 months
- keep coffee in a sealed bag with pressure valve when consumed quickly or in a vacuum container if kept for more than 2-3 weeks