‘Fresh’ is a term in coffee that has been overused by retailers and consumers alike, to the point that it doesn’t mean anything anymore. What is freshness?
Roast dates have become a popular trend amongst quality coffee companies in order to educate the consumer about the importance of having coffee that is roasted recently. The aromatics of coffee only make up for a small percentage of the actual gases in a coffee bean.
The majority of the gas in roasted coffee is carbon dioxide, which slowly diffuses out of the bean allowing oxidation to occur. CO2 helps to protect aromatic volatiles from oxidization, which is why we notice a drop off in the quality of a coffee 10-14 days after it is roasted when a great deal of the CO2 has diffused out of the bean. The structure of coffee is composed of multiple small chambers that trap CO2 and aromatics, which is why ground coffee degasses much faster than whole bean.
Aromatics are flavor. The notes that we taste in coffee are related to the fantastic smells that we experience when we grind coffee. This is why it is so important to grind coffee right before you brew it. The surface area that allows carbon dioxide to escape is at its smallest when coffee is in its whole bean form. If you grind that whole bean up in to tiny bits then you have ultimately increased the surface area exposing most of the coffee to oxygen greatly decreasing the amount of time we can consider your coffee to be fresh. About 50% of the CO2 in coffee is released within the first 5 minutes of grinding.
Think of an apple. If we allow an apple to sit out in its whole form it lasts for quite a long time. If we cut into that apple exposing its flesh it quickly turns brown.
CO2 can be a bit irritating when we are brewing coffee because it is released rapidly in hot water causing the coffee to bloom and rise to the surface of the brew creating a concentration gradient. This is remedied through pre-wetting the grinds to release CO2 before we add the majority of our brew water or by agitating the grinds to produce a more uniform brew. The closer a coffee is to its roast date the more violent the CO2 reaction will be. Coffee with a few days of rest is much more consistent to brew because the CO2 reaction can interfere with the dissolving of brew solids, and coffee with some rest has far less CO2 than it does directly off of roast.
There are many methods that help to preserve the quality of coffee for longer than the roughly 14-day window after it is roasted. Replacing the oxygen in sealed containers with nitrogen can help to protect the beans exposure to oxygen by balancing the atmospheric pressure because it is a similar weight to oxygen, yet doesn’t oxidize the coffees volatile aromatics. Nitrogen flushing does help to preserve quality of flavor while the bag is closed, but as soon as the bag is opened the degradation of the flavor is far quicker than if you package without the addition of nitrogen.
Freezing is also an option, but a labor intensive one. If coffee that is fresh off roast is not an option freezing may be a last resort technique that might work for you. Typically coffee companies will tell you that freezing coffee is a bad idea, but it is the best option if you want to consume coffee at a date later than two weeks off of roast. The moisture in roasted coffee will not freeze at temperatures that your ordinary household freezer can produce because they are chemically bound to the coffees structure. Coffee will however absorb moisture from the air around it so it is important to properly seal coffee that you will freeze. It is best to package the coffee that you put into the freezer into individual portions so that you don’t defrost and refreeze the coffee. Squeeze as much oxygen out of the package as you can and make sure that the package is sealed to not allow any moisture from the freezer to be absorbed by the coffee. As much as I might like my coffee to taste like the bacon in my freezer, I wouldn’t want the freezer burnt tastes that accompany it.