By understanding the factors that compromise coffee freshness, we can further develop strategies to maintain the best flavor for as long as possible. The most common and practical way to store coffee is in coffee bags.
Many roasters carefully choose air-tight bags and use one-way air valves (to avoid degassing of coffee beans and the accumulation of air pressure). Some roasters even pump in an inert gas to remove moisture and oxygen before completely sealing the coffee bag.
When using a one-way air valve coffee bag, the natural escape of carbon dioxide from the coffee will achieve a similar effect if the coffee beans are bagged directly shortly after roasting. A one-way air valve is not an ideal solution because the aroma is also expelled.
In theory, a sealed bag filled with inert gas may remain fresher longer – until the coffee bag is opened for the first time and the seal is broken. At this time, there is less carbon dioxide to push other gases out, and the coffee beans will be more susceptible to damage.
Effects of moisture and oxygen
When the coffee beans are packed in a good quality coffee bag and the seal is still intact, the cooked beans in the bag often stay fresh for an amazingly long time. For example, during a blind tasting, I couldn’t tell the difference between new coffee beans roasted by the same roaster and old beans that had been stored for 3 months. I was a little surprised at first, but then I realized that people are so accustomed to the fact that cooked coffee beans “go bad” very quickly, and this is because we are constantly opening and closing the coffee bag to get the beans. Basically, as long as they remain sealed, a good quality coffee bag is an excellent way to store cooked coffee beans, as the initial escape of carbon dioxide has the effect of injecting an inert gas. Whenever the coffee bag is opened, new water vapor and oxygen will be brought in. However, the carbon dioxide in the bag will be lost over time, and other gases cannot be pushed out.
The most common and powerful way to preserve cooked beans is freezing
When properly frozen, coffee beans can stay fresh for more than 1 year. However, you must be very careful when freezing coffee beans, as it is easy to expose the beans to large amounts of moisture if you are not careful. For example, every time the freezer door is opened, moisture may get in and quickly condense and spread a layer of ice crystals on the surface of any items that are not properly sealed due to the low temperature, including most plastic containers and Ziploc® bags. The one-way air valve of the coffee bag is not specifically designed for cold environments, because the one-way air valve must rely on a thin layer of oily compartment (compartment of oil) to be used, and this mechanism will be severely affected by freezing temperatures. There are also other one-way air valves that can operate at freezing temperatures, such as the silicon-top air valves on Weber Workshop coffee cans.
- When coffee beans are taken out of the freezer, they may remain frozen for several hours depending on how they are packaged.
- When these coffee beans are still in a cold state and come into contact with the air, some moisture will quickly condense on the surface.
If you grind and brew the beans right away, condensation won’t cause much of a problem, but if the beans are left in the bag for any length of time, the cooked beans will begin to decay quickly as moisture builds up. It follows that once you decide to freeze coffee beans, you must handle them with caution: the beans must always remain completely sealed, and only the immediate user can come into contact with the air while they are still cold. Freezing does not seem to damage the internal structure of coffee beans, and I personally have not seen any data that repeatedly freezing coffee beans will cause damage.
Grinding coffee beans while cold
There is some thought that grinding the beans when they are cold makes the coffee taste better (e.g., Uman et al. 2016). While this practice may slightly increase the amount of coffee fines (particle size less than 100 microns), the fines may reduce the quality of the percolation. But in my personal experience, grinding frozen coffee beans still seems to improve the quality of filter coffee, perhaps because the frozen state retains more of the coffee aroma during grinding.
Although it has been mentioned before that heat is the enemy of coffee beans, I still want to emphasize it again: please keep the coffee bean container away from heat sources. A 2001 study by Labuza et al. calculated that the shelf life of coffee beans at 22°C would be 21 weeks, but that the same packaging would be reduced to 16 weeks at 35°C (see also Illy and Viani 2004).
