Last Updated on May 17, 2022 by John Moretti
Anyone interested in coffee and brewing fresh coffee has heard the term ‘degassing.’ This process is also referred to as ‘resting’ or ‘outgassing,’ but these terms all refer to the same thing. If you buy very fresh coffee beans from a local roaster, it may be frustrating to find out that you need to wait a while before brewing the coffee for the best results, but is this really necessary?
Degassing coffee is necessary if the coffee beans are freshly roasted. Degassing is not necessary for beans that were roasted weeks ago. Light roast coffee beans must be degassed for longer than medium and dark roast coffee. Degassing allows coffee to extract effectively during brewing.
Degassing coffee may seem unnecessary, but there is a good reason why coffee roasters recommend letting your coffee rest for a while before brewing. Let’s dive a little deeper into the process of degassing coffee to find out why it’s important and when it is necessary.
Why Is Degassing Coffee Important?
Everyone loves a fresh cup of coffee. There is almost a no better way to start the day, and there is almost no beverage tastier than a freshly roasted, freshly ground, freshly brewed cup of good coffee. However, freshness is relative to coffee, and how fresh coffee beans are can affect the taste of the brew in positive and negative ways.
When coffee beans are roasted, they produce a substantial amount of carbon dioxide gas. This is a by-product of the chemical processes that occur during roasting, as the structure of the coffee bean breaks down and becomes more soluble.
Most of the gasses escape the beans during the roasting process, but some are left trapped within the bean after roasting. Resting or degassing coffee beans allows most of this leftover gas to leave the beans.
This process is important because when water comes into contact with the coffee beans during brewing, the gas in the beans escapes much more rapidly. If there is a lot of gas in the beans during brewing, the gas can negatively affect the taste of the brew by adding a mild carbonic acid flavor to the liquid, similar to the taste of flat carbonated water.
However, the main issue with rapidly escaping carbon dioxide while brewing is that it prevents even extraction. If there is a lot of gas in ground coffee beans while brewing, the gas rapidly escapes and forms a small gas bubble around each grain of coffee as water touches it.
This gas bubble prevents the water from contacting the entire surface area of the coffee, which, in turn, prevents the coffee from extracting efficiently. This leads to a lackluster, underwhelming, under-extracted, sour cup of coffee.
This problem is exacerbated by certain brewing processes that involve high heat or high pressures, such as espresso brewing. The full extent of the problem is all dependent on how the coffee beans are roasted, as there is less gas left in lightly roasted beans compared to dark roasted beans.
All of this means that degassing coffee is important, but it should not be left to rest for too long to prevent the coffee beans from going stale before grinding and brewing.
Is Degassing Coffee Always Necessary?
We have established that degassing coffee is crucial for even extraction and for achieving a good tasting coffee brew, but is this process always necessary when you buy a bag of coffee?
The answer to this is dependent on how you buy your coffee. The truth is, coffee will degas on its own in its packaging, which is why most bags of coffee beans or pre-ground coffee have built-in degassing valves.
Degassing is always necessary if you buy very fresh coffee beans. If you buy freshly roasted coffee beans from a local roastery, especially a roastery that roasts coffee beans to order, the coffee that you buy is likely to be shipped to you on the day that it is roasted.
This means that depending on how far away from the roaster you live, the coffee will be extremely fresh when it arrives at your home. If this is the case, it is important to allow the coffee to rest and degas for a while before grinding and brewing.
This is very important for lightly roasted beans because the gas trapped within the beans takes longer to escape, as the beans themselves are denser compared to darker roasted beans.
Dark and medium roasted beans do not need to be rested for as long, but degassing is still necessary for achieving the best brew possible.
However, if you buy coffee beans or pre-ground coffee from a supermarket or some other type of wholesaler that retains a lot of stock before selling each item, then degassing is probably not necessary. This is because the coffee beans are likely to have been stored in a warehouse or on a shelf for a time before you bought them.
These coffee beans would have degassed sufficiently within their packaging during storage, which means that no waiting is required at all before grinding and brewing.
How Long Should You Rest Coffee?
If you do buy freshly roasted coffee, understanding how long to rest the coffee to allow it to degas is important. This will determine how long your coffee stays fresh and how good your brews taste.
The amount of time that coffee beans should be rested is largely dependent on how you brew the coffee. If you prefer to brew with pour-over methods or immersion brew methods, then the coffee does not need to be left to degas for very long.
If you brew with high-pressure methods, such as espresso brewing, then the coffee must be allowed to degas for much longer.
If you use pour-over or immersion brew methods, lightly roasted coffee beans should be allowed to degas for 3 – 5 days before grinding and brewing. Medium and dark roasted coffee beans can be let for only 2 days before grinding and brewing, as they degas more quickly.
If you brew with high-pressure methods, then light roasted coffee beans should be left to degas for no less than 10 days before grinding and brewing. Medium roast coffee beans will need 8 – 10 days before roasting, and dark roasts will require a minimum of 5 – 8 days to degas before grinding and brewing.
Resting the coffee beans in this way will provide the best tasting brews, and the act of brewing itself will be far less challenging.
The truth of it all is that freshly roasted coffee beans must always be allowed to degas to some degree after roasting, or the coffee will not taste as good as it should, and it will not extract well during the brewing process.
The length of time required for degassing is relative to the brewing process that is used and the degree to which the coffee beans are roasted. For the best results, never allow coffee to degas for too long, or the beans may become stale. Once the coffee beans reach their optimum state, keep them in a cool environment to slow down the degassing process.