Why Does Coffee Degas & What Does It Mean For Brewers & Roasters?

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The fresher a coffee is, the better – right? Well, yes… but also no.

Even though nobody wants to drink stale coffee, brewing a coffee straight after roasting can also result in a disappointing brew. That’s because of coffee degassing.

Whether you’re a roaster or brewer, you need to know about this. So, let’s explore what coffee degassing is, how it can affect your brew, and what you should do about this.

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Coffee beans cool down after roasting. Credit: Neil Soque

What Is Coffee Degassing?

Degassing is the release of gases from roasted coffee. When you roast coffee, gases – including a lot of carbon dioxide – form inside the bean.

A lot of these gases are released in the first few days after roasting. The problem is that the escaping gases can result in small bubbles when you brew your coffee. These air pockets can disrupt the contact between the coffee grounds and the water, leading to an uneven extraction of the flavour and aroma compounds in the dry coffee.

In other words, if you brew coffee that has just been roasted, it can negatively affect the flavour of the coffee.

Discover more! Check out Understand Coffee Extraction for Better Coffee

Because of this, it’s a good idea to wait a few days after roasting before you brew your coffee. This period of time and the chemical release that happens during it are known as degassing.

Fresh coffee beans. Credit: Julio Guevara

Why Is There Carbon Dioxide in Coffee Anyway?

Between the first and second crack in roasting, coffee beans undergo a process called pyrolysis. At approximately 220°C/430℉, sugars are broken down into different compounds, including carbon dioxide. The beans begin to brown and become smaller due to the water loss.

Ensei Neto is the founder of The Coffee Traveler. He tells me that “pyrolysis is the most important chemical reaction at the end of roasting, because [this is] when conversion of sugar happens. When the energy is released, it makes gas.”

A cut roasted coffee bean, exhibiting different levels of development. Credit: Ensei Neto

Coffee Degassing: Getting It “Just Right”

But carbon dioxide in your beans isn’t a bad thing: it has an important role in coffee quality. “It is an indicator for freshness, plays an important role in shelf life and in packaging, impacts the extraction process, is involved in crema formation, and may affect the sensory profile in the cup,” says a 2018 report in the Journal of Agricultural and Food Chemistry.

When a coffee has degassed too much, the flavours are less vibrant. The trick is to allow it to degas sufficiently, without allowing the beans to become stale. As Juan Mario Carvajal, Co-Founder of the Latam SCA, tells me, “The gas still being released is an indicator of freshness, but when it is too fresh it prevents the coffee grounds from being fully extracted.”

If you use coffee that hasn’t degassed for long enough, it can take longer to pull a shot of espresso because the gases impede the water. These gases can help produce an impressive-looking crema because they create bubbles. But the flavour will be less than ideal because they have also interrupted extraction.

Joe Behm is the President of Behmor, which manufactures SCA-certified home roasters and smart brewers. He tells me that it is important to degas coffee to allow flavours to shine.

He gives an example of roasting a Guatemalan coffee in his award-winning Behmor 1600 Plus. After 72 hours, he says, it had a rubbery flavour. But after 96 hours, the chocolate notes were clearer and “the coffee character had built”.

Coffee beans roast in the Behmor 1600 Plus. Credit: Behmor

How Much Time Is Needed For Degassing?

So, degassing allows the dispersion of carbon dioxide caused in the roasting process. But we don’t want all of this gas to disappear. Instead, we should brew when there is just enough of it present. The right amount of carbon dioxide stops the coffee tasting stale and flat.

But how long after roasting this is depends on several factors. Generally, somewhere between three days and two to three weeks after roasting is considered a good time to brew coffee. Yet every coffee is different and the degassing period needed will vary. The brewing method, processing choices, and roast profile all affect how long this is.

Sharayah Harper, Co-Founder of Uncharted Coffee Co in Pueblo, Colorado, USA, says, “The harvesting and the washing process is always different, the drying process is always different, the water content is always different. So, I believe that is why [degassing] varies… Different sizes of beans, different quantities of moisture and gas.”

Roasted coffee beans stored in a metal container. Credit: Maria Fernanda Gonzalez

  • Brewing Method

If you are using beans for a pour over or French press, you can probably use them as quickly as a couple of days after roasting. This is because the coffee has longer contact time with the water.

In contrast, when we pull an espresso shot, the tiny brew time means the carbon dioxide bubbles have a bigger effect on extraction.

Joe tells me, “Espresso is special. It needs rest time. You will not see an espresso coffee freshly roasted and then brewed… Coffee resting is critical, and degassing is important to the coffee flavours.”

Mark Michaelson is the Head Roaster at Onyx Coffee Lab and 2017 US Roasting Champion. He tells me, “We typically like our coffees to be five to seven days off roast for espresso purposes, mainly because it is easier to pull this coffee. For [manually] brewing coffee, one or two days.”

He also explains that, when Onyx coffee is used in competitions, it is usually 10 to 21 days off roast. “Because it makes easier to pull the coffee, it is easier for the extraction,” he says.

“If you can wait three to five days after the roast to start dialling in your coffees, it will really help your staff members not to get so angry with the inconsistency of the coffee,” he adds.

Dosing coffee into the portafilter, ready to pull an espresso. Credit: Neil Soque

  • Processing Method

Washed, natural, honey: how a coffee was processed can also affect the degassing. Mark says, “We have noticed that natural coffees need longer times to degas than washed.  

“I notice with naturals that three to five days off roast is sometimes when you can find a bit of freshness. Naturals need to take a little bit more time to open up for degassing than a washed coffee.”

Learn more in A Roaster Champion’s Guide to Roasting Natural & Honey Processed Coffees

The SCA-certified Behmor 1600 Plus and Behmor Connected Brewer. Credit: Behmor

  • Roast Profile

A dark roast accelerates degassing because the bean has degraded more. The sugars have had more opportunity to be transformed, and there are more tiny cracks allowing the carbon dioxide to be released.

Sharayah tells me, “With a light roast, you have more of the bean intact.” This means the lighter roasts might need to degas for longer.

And Ensei reminds me that, if a roast is uneven, it can lead to layers within the bean. These can degrade at different times, depending on their level of development, and this changes the rate of degassing.

Sharayah prepares to roast Colombian green beans from Planadas, Tolima. Credit: Sharayah Harper

How To Keep Roasted Coffee Fresh

How do you make sure that you’re drinking coffee that has degassed the “right” amount?

Sharayah recommends having a good organisation system so that the roasted coffee doesn’t sit for too long. “Keeping a really solid record is very helpful for us, especially with very large quantities,” she says.

Mark tells me that Onyx uses a nitro flush system to seal their bags. “With it, the shelf life is much longer,” he says.

He typically bags coffee anywhere from 20 mins to an hour after it has been roasted, but those bags contain a degassing valve. “Most of our coffees are travelling at least three days [to the customer]. We just want to allow some degassing, especially when travelling, to allow the coffee to calm down a little bit.”

Removing freshly roasted coffee from the roaster. Credit: Behmor

Tips for Home Roasters

Home roasters may not have access to nitro flush systems, but they also don’t have the problems of large coffee volumes and global logistics.

Joe explains that “if you work under the premise that coffee begins to lose its flavours within seven days of being roasted, then at the eighth day you tend to lose some character in the coffee.”

He tells me that as soon as he opens a container of green coffee, he roasts it and lets it rest for four days. “That way I just do a natural, constant rotation. I open a Guatemalan coffee today and I want an Ethiopian coffee in four days, so I roast an Ethiopian coffee and then four days later, I have a nicely rested coffee,” he says.

Joe also reuses large yoghurt pots to store his roasted coffee. “Because they are not airtight, so the gas can leak out. They are not exposed to the sunlight because they are white plastic. So, you don’t get the infusion into the plastic, you don’t get the sunlight destroying it. For me, it is the ideal container.”

We often see airtight containers promoted as ideal for coffee storage to “keep the freshness in”. But when you’re using freshly home-roasted beans, the container should allow carbon dioxide to escape. And you should consider roasting in batch sizes that allow you to use all of the coffee before it becomes stale.

Putting green beans into the roaster drum. Credit: Behmor

Degassing: it can be the difference between a delicious coffee and a disappointment. But it doesn’t have to be complicated. It’s just a matter of allowing roasted beans time to release excess carbon dioxide.

So remember, know when your beans were roasted. Consider your storage systems and brewing methods. And don’t forget that every coffee bean is different: some will take longer than others to degas. If a coffee is a few days off the roast but not yet extracting as you want, give it a little more time. Just don’t leave it all month.

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