Degassing Coffee; yes, coffee can be ‘too fresh'
Are you a fellow home roaster? You probably got started roasting at home as a way to avoid the stale coffee you often find at the store or coffee shop. While we admire your choice, you may not know that coffee that is too fresh can be just as bad as stale coffee.
Degassing your coffee is a process that helps you strike that perfect flavour balance so you get the most from your roast. Keep reading to learn more and figure out how to incorporate this into your coffee routine!
What is ‘coffee degassing?'
Degassing is a natural reaction that begins once the coffee is roasted. After roasting, the beans start losing the gases that were formed inside them during the roasting process, consisting mainly of carbon dioxide.
Any attentive brewer knows that the right level of CO2 in your beans can actually enhance flavour extraction, while too much can spoil the taste of your coffee. If the coffee beans haven’t degassed properly and therefore maintain too much carbon dioxide, the gas will escape in small bubbles during the brewing process and your coffee’s flavour will suffer. (1)
These air pockets can disrupt the contact between the coffee grounds and the water, leading to an uneven extraction of the flavuor and aroma compounds in the dry coffee.
If you're trying your hand at home roasting don't skip this step: it can make or break you as a roaster.
Why do coffee beans emit CO2 in the first place?
Given the vast difference in aroma and appearance of coffee beans pre- and post-roast, it’s clear that lots of chemical reactions have taken place. As the beans brown, the heat breaks down complex carbohydrates into smaller molecules and creates vapour and carbon dioxide. It’s thanks to this build up of gases that enough pressure is created to break the bean’s cell wall and produce the first crack.
The majority of CO2 appears towards the end of the roasting process, due to the release of energy that occurs with sugar transformation.
How long do coffee beans need to degas?
Much like hops in beer and grapes in wine, there are lots of different types of beans when it comes to coffee, so degassing time depends on a set of factors specific to the beans. Harvesting techniques, drying process, bean size, and type of roast, are all important elements that determine how long beans will need to release the appropriate amount of CO2.
Generally speaking, while around 40% of all CO2 is released within 24 hours after roasting, degassing can take from 2 to 14 days.
The golden rule when it comes to degassing is to be patient. This means waiting to grind your beans and storing them properly. While grinding your freshly roasted coffee can make the degassing process go faster, it does so in the same way using K-Cups can give you a quick cup of joe, which is to say, we don’t recommend it. Doing so will get rid of pretty much all their carbon dioxide and volatile compounds that add flavour, resulting in stale coffee. Let your beans degas and only grind just before brewing to ensure the freshest possible taste. Relax, it's just a couple of days!
So we have said that patience is key when it comes to degassing, it is also important not to let your beans sit for too long. As we mentioned before, some degree of carbon dioxide is extremely good for your brew: it is an indicator for freshness, helps preserve the flavours and aromas of your coffee and gives you a thicker crema when it comes to espresso. (2)
The final factor to consider when degassing your coffee is your brew method. Given that pour over and French press brews leave the coffee in contact with the water for longer than, say, an espresso, they don’t need as much degassing. The primary factors here have to do with the time during which the coffee is exposed to water.
Since the extraction time is very short in an espresso brew, any releasing air bubbles can slow down the hot water and mess up the brew.
How do you know if your coffee beans are degassed or still need time?
If you buy freshly-roasted beans, you can usually rely on the “best before” date, but if you’re roasting them yourself you may be in for a bit more trial and error. However, there are a couple of tricks that you can use to see how fresh your beans are a few days after roasting.
If your dark roast is starting to lose its oily look and is not leaving any residue when you touch it, then you should grind those beans before it’s too late.
While it can be harder to tell with lighter roasts, a general rule is that you want your beans to be shiny but not oily. You can also do a quick test by chucking a handful of roasted beans in a resealable plastic bag, pressing out the air and leaving it overnight. If the bag is puffed up in the morning, there is still some carbon dioxide releasing, meaning your beans are nice and fresh.
How do you keep roasted coffee fresh?
The fact that you must wait a few days before grinding your beans doesn’t mean that you should look after them any less! Make sure to properly store your roasted coffee in an airtight container and kept in a dry place to protect it from oxygen and moisture, but wait 24 hours before sealing it in order to avoid CO2 pressurization.
If your coffee is not correctly stored, you can count on it going stale much faster.
Brewing Fresh Coffee: The Bloom
The final step in degassing actually takes place during brewing. Pre-infusing your coffee allows the remaining trapped CO2 to escape to ensure a fuller extraction. This final release, called the bloom, is triggered by the exposure of the beans to hot water. We talk more about blooming coffee here.
To effectively pre-infuse your coffee, allow just enough hot water to cover or saturate the grounds, and let it rest for 30 seconds. When you brew fresh coffee, the remaining CO2 will immediately react with hot water in the form of bubbles. (3) While this technique is mainly used with pour overs and French presses, more and more automatic drip brewers and espresso machines are including this useful function.
Degassing is a delicate process influenced by a myriad of factors, all of which is to say that it is hard to get exactly right. Now that you have a solid understanding of how it works, you can begin to test it out with your beans at home. We’re sure that, with a bit of practice and experimentation, you’ll be able to find the best degassing time for your beans and make the most of your home brewing experience
Coffee bags have valves in order to let the freshly roasted coffee degas. These one-way valves let CO2 out without letting oxygen in to spoil the coffee. When coffee bags don’t have these valves, the releasing CO2 remains within the bag, puffing it up and sometimes even causing it to explode (for real!).
Given the high pressure used in espresso machines, the CO2 that releases upon contact between roasted coffee and hot water reacts a bit differently than in a french press. The pressure creates lots of tiny bubbles that result in a foamy layer of crema. While some CO2 is good for espresso and full-bodied crema, too much can actually slow down extraction. An overly-gassy espresso shot may look nice, but it will taste sour and sharp.
- Molina, A. (2019, January 2). Why Does Coffee Degas & What Does It Mean For Brewers & Roasters? Retrieved from https://perfectdailygrind.com/2019/01/why-does-coffee-degas-what-does-it-mean-for-brewers-roasters/
- Smrke, S., Wellinger, M., Suzuki, T., Balsiger, F., Opitz, S., & Yeretzian, C. (2017, November 1). Time-Resolved Gravimetric Method To Assess Degassing of Roasted Coffee. Retrieved from https://pubs.acs.org/doi/full/10.1021/acs.jafc.7b03310
- (n.d.). (2017, November 25). Allow your coffee to bloom. Retrieved from https://www.stravacraftcoffee.com/blogs/the-roasters-voice/allow-your-coffee-to-bloom