Understanding Degassing: Is Fresh Best?
Understanding Degassing: Is Fresh Best?

We’re diving deep into the gassy world of fresh coffee beans to understand why “fresh” isn’t always best.  

So what is degassing?

When coffee is roasted, gases form inside the bean. After roasting, gases (mostly carbon dioxide) start seeping out. When coffee is a few days old and very fresh, a bulk of the carbon dioxide formed leaves your beans. During this time, CO2 escapes so quickly it negatively affects the flavor of your coffee by creating an uneven extraction. This degassing process is the reason roasters start selling their coffee a few days to a week after the roast date.

How long does it take for beans to degas?

Degassing varies depending on the type of coffee and roast. It, therefore, can take anywhere from 2 to 12 days until the coffee is ready to brew. Some rules of thumb:

  • The first 24 hours is when a bulk (approximately 40%) of CO2 leaves the bean.
  • Darker roasts usually degas faster than lighter roasts.
  • Longer roasts usually degas faster than faster roasts.

Your roaster or barista will have a good idea of when it’s best to start brewing. Often, your roaster won’t sell their coffee until it’s good to go.

Why you shouldn’t pre-grind your beans to speed up degassing!  

If you grind your coffee well before brewing, degassing significantly speeds up (but not in a good way). The finer the grind, the larger the gas volume is released – making your coffee stale in a matter of hours. This is because the more you grind, the more cells that store these gases are broken up and released. You’re also speeding up the oxidation process by exposing your coffee to oxygen (we’ll cover oxidation in a minute).

What happens when you brew freshly roasted coffee?

The fresher your coffee the more degassing you will experience during your brew. This is why it’s important to bloom your coffee (pre-wet and let sit for around 30 seconds) in order to release rapidly escaping CO2. However, if your coffee is to too fresh, regardless of how you brew your coffee, the extraction will still be uneven due to the overwhelming amount of CO2 escaping during the entire brewing process. 

What happens once beans have degassed?

Much like a fine wine, freshly roasted coffee gets better with time…well, to an extent. After the first few days of degassing, oxygen starts to make its way into your beans. This is called oxidation and is the main cause of staleness. A way to prolong the flavor of your coffee is to store it in a container with a one-way valve. This way, CO2 is able to escape, and oxygen won’t as easily find its way in.

To sum up, “fresh” isn’t best if you’re dealing with freshly roasted coffee (mind you, if we’re talking fresh as in roasted recently and degassed, versus months old grocery store coffee – that type of fresh is always best!)

Always consult your roaster on how many days you should wait until brewing. You want to find that sweet spot between freshly roasted and oxidized for a perfect cup.

(Photography courtesy of Chloe Wen)