The term “fresh coffee” has varied meaning depending who you ask. To some, it may mean beans that are still warm off the roaster. To some, it may mean beans that were roasted within a week. And then to others, it may mean a bag brought home from the grocery store and just opened. Today we’re discussing what makes a coffee “fresh” and how we determine its shelf-life.

For the purposes of this article, we’re using the word “fresh” to say when coffee is most flavorful and aromatic.

Although a coffee’s characteristics can be attributed to its growing region and processing method, the majority of a coffee’s flavors are developed during the roasting process. When coffee is unroasted and still in green bean form, it smells similar to fresh produce because that’s essentially what it is! But roasting changes the physical and chemical nature of coffee. This is where we begin to smell the amazing aroma of coffee, much like bread baked in the oven.

However, while roasting is the very process that makes a bean flavorful and aromatic, it also is the main contributor to the acceleration of a bean’s staling process. This is because while roasting, the coffee’s sugars and amino acids breakdown. This occurrence builds up carbon dioxide within the bean. After the bean has been roasted, it immediately begins to off-gas (release carbon dioxide). Why do coffee bags have that little vent? Now you know: it’s a one way valve, releasing gas!

Off-gassing is necessary for the bean to become easy to brew. If too much carbon dioxide is present in the bean and the bean is met with hot water, bubbles form. Some bubbles are good! — and are a good indicator that the beans have been recently roasted. But too much may inhibit the coffee from even water contact, thereby creating an uneven flavor extraction. That’s why you’ll see baristas letting a coffee “bloom” as they brew your coffee at the pour over bar. This is especially magnified for espresso (which should rest a couple days longer) since it is experiencing pressurized water for only a few seconds.

Typically, whole beans have sufficiently off-gassed within 3-4 days of roasting. Ground beans will off-gas at a much higher rate because of its increased surface-to-volume ratio. Nailing a great time to brew beans is like going after a moving target. A great barista is attempting to capture the bean’s flavor profile just after it has off-gassed enough, yet before the coffee begins to lose its flavor compounds due to the elements of temperature, moisture and oxygen.

The prime culprits of coffee staling after the beans have roasted are temperature, moisture and oxygen. At warmer temperatures, the coffee degases at a more rapid rate. Conversely, it is slowed down at cooler temperatures. We recommend to keep roasted beans away from humid environments as it also has a positive correlation to coffee staling as the beans absorb moisture. Finally, oxygen not only speeds up the loss of flavor compounds in coffee, but it can also create unpleasant tastes in coffee because of the way it oxidizes lipids of the bean. The interaction of oxygen, oils, light and bacteria can make a bean turn rancid. This is especially true for dark roasted beans where the oil is visible on the surface of the beans and more susceptible to rancidification.

To preserve coffee freshness and protect it from these elements, store beans away from heat (not in the cabinet above the stove). We love Airscapes which are food storage canisters that have a valve to keep oxygen out while letting carbon dioxide out. We also recommend getting beans from a local roaster where you can see the roast date (or a mail-order coffee subscription!), and only purchase enough beans for home that you would consume within 2-3 weeks. Otherwise: freeze those beans!