If you’re becoming more of an avid coffee roaster or just learning about all the ways to make a perfect cup of coffee, you might have heard the term coffee degassing or coffee resting.

Understanding what this means and ensuring you get it right can do wonders for your final cup and change how you view your coffee preparation ritual.

Freshly roasted medium roast coffee
Medium roasted beans freshly out of the roaster via PxHere

What is Coffee Degassing?

Coffee degassing is a process whereby carbon dioxide and other gases are slowly released from coffee beans after roasting.

These gases are formed within the coffee bean during roasting and need some time to escape from the beans before brewing. This is why degassing is sometimes referred to as coffee resting – the coffee literally needs to rest in order to allow the gases to release.

Coffee being roasted in a roaster
Coffee during the roasting process via Pixabay

Why Does Coffee Need To Be Degassed?

Coffee that hasn’t been degassed or rested will lead to unevenly extracted coffee. This is because the tiny bubbles will start to escape as soon as the hot water comes into contact with the coffee preventing the hot water from penetrating and extracting the coffee entirely.

The main aspect of the coffee that is impacted as a result of brewing coffee that hasn’t fully degassed is flavor. Specifically, your coffee may end up tasting a little bit too acidic and bitter.

If you’ve ever made coffee using a pour-over or a french press, you’ve probably already seen carbon dioxide escape from the coffee. When bubbles start to form on coffee that has just come into contact with hot water, this is carbon dioxide escaping.

Some methods of brewing coffee actually involve a step that allows the gasses to be released in order to ensure proper extraction. This step is called the bloom and is achieved by pouring water on the coffee and giving it 30 – 45-seconds to release the gasses after which the rest of the water is poured, extracting the remaining coffee more evenly.

How Long Does Coffee Need To Be Degassed For?

The amount of time that coffee needs before it’s ready for brewing depends on many factors. Although over 40% of CO2 is released within the first 24 hours after roasting, the brewing method, processing method, roast profile, coffee variety, and even bean size can all impact the ideal amount of time you should allow for degassing.

However, the most impactful factors that are easily controlled are brewing method and roast profile:

  • Brewing Method: Some brewing methods give the coffee more time to be in contact with the hot water giving the gases enough time to escape and allow for proper extraction. Other methods, like espresso coffee, would usually need more time to degas because the amount of time the coffee is in contact with the hot water is extremely short. This table can be used as a general reference:
Espresso Coffee7 – 14 days
Filter and Pour Over Coffee2 – 7 days
Aeropress Coffee2- 7 days
French Press Coffee 2 days minimum
  • Roast Profile: As a general rule of thumb, dark roasts need less time to degas than light roasts. This is because the longer coffee is roasted for, the more porous it becomes, allowing more gases to escape in a shorter amount of time. If you’re roasting and storing coffee yourself, you’ll need to take this and the brewing method into account before grinding and brewing your coffee.
Brewed coffee with a thin layer of crema
Espresso coffee with a thin layer of crema via Needpix

Why Does Coffee Contain Carbon Dioxide?

When coffee is exposed to heat during the roasting process, many chemical reactions take place. These chemical reactions start with the browning of the coffee bean and end with a fully roasted bean, rich in gases.

The first indication of a chemical reaction is when the bean starts to change color, from green to yellow indicating the start of sugar development. Next, complex carbohydrates start to break down into smaller molecules and again, the bean changes from a yellow color to brown – marking the beginning of caramelization.

At this point, any moisture within the bean turns into water vapor and carbon dioxide begins to form within the cell walls in the bean. The formation of these gases leads to a pressure build-up at which point there is a breaking of the coffees’ cell wall and it experiences its ‘first crack’. This is marked by a popping or cracking sound, similar to that of popcorn popping.

When roasting stops and the beans begin to cool, the formation of new gases comes to a halt and gases within the beans start to escape – degassing!

How Important is Coffee Degassing?

Coffee degassing can be extremely important for anyone looking to bring out all of the great flavors in a particular coffee. Coffee that isn’t given time to degas before brewing can end up being ‘too fresh’ and may develop unfavorable bitter and acidic flavors while coffee resting for too long will almost certainly go stale. This is very important for anyone who is looking to control all of the variables leading to a perfect cup of coffee.

While coffee degassing can be very important, the improvements in taste and flavor that result from a sufficiently degassed coffee might be so minor that they would be difficult for most to discern.

While all roasted coffee should be degassed for at least 24 hours and 2 – 14 days is the absolute sweet spot for most coffees and brewing methods, a discernable loss of vibrancy and higher acid notes only begin to reveal themselves two months after roasting. Some coffees can taste fine even 6-months after roasting.

How to Know If Your Coffee Has Degassed Enough?

When it comes to degassing your coffee, patience is absolutely essential. Simply giving your coffee a few days after roasting while storing it correctly will ensure the coffee is degassed properly.

If you’re buying freshly roasted beans, you can rely on the best before date to determine when the beans are ready for grinding and brewing.

However, if you’re roasting the beans yourself, you can use a simple trick to find out if they’ve had enough time to degas: place them in a small resealable bag and press out all of the air. Leave the beans in the bag overnight. If the bag has expanded by morning, then the beans likely need more time to degas.

Pour over coffee during the coffee bloom via Joe St. Pierre on Flikr

Should You Grind Freshly Roasted Coffee to Speed Up Degassing?

If you’re dealing with time constraints or just can’t wait to try that coffee you recently roasted, then you may have considered grinding freshly roasted coffee in order to speed up the degassing process.

This is something you definitely should not do. The reason for this is because grinding roasted coffee beans causes them to degas at a very fast pace, effectively making your coffee stale – a process that would normally take months.

Once again, the key to achieving the ‘right’ amount of freshness with your roasted coffee beans is simply patience. Give your beans time to rest and only then should you put them in the grinder.

How to Keep Roasted Coffee Fresh

As soon as coffee comes out of the roasted and the gases start to escape, and oxygen starts to seep in. Oxygen entering into the coffee is the main cause of staleness and the process is known as oxidation.

The best way to keep coffee fresh and prevent it from going stale is to store it in a low-oxygen environment.

If you’re storing your freshly roasted coffee in a sealed container, like a jar, its best to keep the lid loosely open to prevent a build-up of pressure. However, placing it in packaging with a one-way valve (the way most supermarket coffee is packed) is the best way to store it to allow for degassing. You might have seen these valves in any standard coffee packaging – these small plastic valves allow for air to be released but restrict air from entering the packaging. They’re are ideal for recently roasted coffee that needs time to degas.

If your coffee beans have had time to degas and you’re looking for slightly longer-term storage space, its best to store them in an airtight container. These come in many different shapes and sizes and are the best option to prevent staleness.

Final Thoughts

Degassing is a very important step for any coffee roaster. Ensuring that your beans have had enough time to release the carbon dioxide and other volatile gases can be the difference between an under-extracted cup of coffee and an incredible full-bodied cup.

While finding the optimum amount of time for degassing can be difficult, there are a few guidelines and rules you can easily follow to make sure that your coffee is sufficiently degassed and ready for brewing!

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