Some say roasting coffee is a combination of art and science, well the same can be said about packaging coffee. It is much more complex than just pouring roasted beans into a bag.
Large coffee companies have expensive gas-flushing modules in their production lines and medium to small companies often use bags with one-way valves and are picky about roasting dates. Why is that?
Well, it is because coffee goes stale. There is a lot behind that statement, and to get a better understanding of what that entails and more importantly why we need to understand the chemistry fundamentals of a roasted coffee bean.
A roasted coffee bean contains over a thousand chemical compounds, which are a result of several chemical reactions (e.g. the Maillard reaction and Pyrolysis) caused by heat. During the roasting process, the green bean transforms into a very unstable and reactive system.
The second the beans hit the cooling tray of the roaster they are attacked by the surrounding environment. Moisture, light, and heat but the most damage are done by volatilization and oxidation. Freshly roasted coffee release large amounts of gas (mostly carbon dioxide), which in turn is replaced by oxygen resulting in the oxidation of flavor compounds inside the roasted coffee bean. The release of gas which also includes loss of flavor components continues throughout the bean’s lifespan all the way to consumption.
However, degassing isn’t all bad, and right after roasting it is a good thing, coffee that hasn’t had enough time to degas may generate bubbles during brewing, leading to an uneven extraction which may negatively impact the flavor and aroma of your coffee.
In summary, the presence of carbon dioxide is often a sign of freshness but due to degassing, oxidation causes your coffee to taste bad and volatilization causes your coffee to taste bland.
So where does this leave us? Fortunately, coffee staling is a gradual process so it’s not all or nothing but if you want the most of your freshly ground beans you have to brew them within 20 minutes of grinding. If you are using pre-ground coffee this could mean that you are only getting one cup of fresh, flavorful coffee per bag.
When it comes to whole beans the stats are a bit better since whole beans have vastly lower surface area compared to ground beans but we are still talking about days not months. So not much better unless you are drinking 15 double espressos a day, using an opened 500 g bag of coffee as a reference.
Now the above describes the worst-case scenario, where the beans are stored in the open air without any protection from the elements or in a semi-open container in direct contact with air. However, if any of this rings a bell you might want to improve the way you store your coffee.
Worth mentioning, that if you are only drinking coffee as a stimulant, you are in luck. Whole beans, ground or brewed, will keep the same amount of caffeine for a long time. Caffeine is a pretty stable compound and doesn’t degrade quickly, it takes years before any significant change is observed.
Anyways let’s get back to packaging and more specifically MAP which stands for Modified Atmosphere Packaging, and exactly as it sounds, the atmosphere surrounding the product within the package is actively or passively modified. When it comes to perishable food items like coffee, the most popular methods are gas flushing or the use of bags with one-way valves, or a combination of the two.
During a gas flush process, usually nitrogen is pumped into the bag before sealing to displace ambient oxygen which drastically decreases the rate of decay that otherwise could be 20 times faster in the presence of oxygen.
A similar but less effective way (in terms of staling) is to package the beans shortly after roasting them in bags with a one-way valve. This limits the exposure to oxygen and the valve will only allow gases to leave the bag and not enter but without the active flush, there will be oxygen trapped inside the package that will speed up the degradation. In both cases, the lack or absence of oxygen also decreases the growth of aerobic spoilage organisms.
In short, the packaging process of coffee is not just the final step, but an extremely important one for maintaining the freshness, integrity, and shelf-life of ground or whole bean coffee, so that the coffee you buy is in pristine condition, and tastes as the roaster intended it.