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The Science Behind Coffee Degassing

Freshly roasted coffee beans enhance the taste of your cup of coffee. While we encourage people to roast their own coffee beans, coffee that is too fresh can be as bad as stale coffee. Degassing your coffee beans is an important process that can help you get the right flavour balance for the perfect tasting coffee. In this blog, we’ll talk you through what degassing is and the science behind the process.

What is Coffee Degassing?

Degassing is the release of gases from roasted coffee beans. When you roast coffee beans a build-up of gases which includes carbon dioxide forms inside the beans. Lots of these gases are released a couple of days after roasting. Gas within your coffee beans can cause  small bubbles to form when you brew the coffee. These small bubbles can interrupt contact between the water and the coffee, this can lead to an irregular extraction of the flavour compounds inside the coffee. Simply put, when you brew coffee has been roasted recently, it can harm the flavour of your coffee. To tackle this process, it is a good idea to wait a few days before you brew the coffee after roasting. The chemical reaction and the time it takes to react is known as degassing.


Why do Coffee Beans Emit CO2 Anyway?

As there is a huge difference in appearance and aromas of the coffee beans before you roast and after,  it’s quite obvious that there are lots of chemical reactions taken place. As the beans roast, the heat starts to break down the carbohydrates into smaller molecules and produces vapour and carbon dioxide. Most of the CO2 produced occurs at the end of the roasting process, this is directly due to the release of energy that occurs during the transformation of the carbohydrates.

What is the Length of Time Needed for Degassing Process?

Degassing enables the carbon dioxide that is produced during roasting to disperse. It’s important to remember that you don’t want all of the gas to disperse. You need to start brewing your coffee when there is still some present. The correct balance of carbon dioxide ensures that the coffee isn’t stale when consumed.

How Long after Degassing should you Brew?

There is a whole debate on the length of time that you should allow, however, in general we suggest between three days and two weeks. This depends on the type of coffee beans you’re using; the degassing period will need to vary. Many factors influence the degassing period which includes the roast profile, processing and the brewing method.

How do you know that your Coffee Beans have been Degassed?

If you have purchased freshly roasted coffee beans, you should often go on the best before date written on the packaging. However, it’s more of a trial-and-error process if you’re roasting the beans yourself. Here are a few tips you can use to know just how fresh the beans are.

  • Once your dark roast is losing its oily look and feel and isn’t leaving any remains when you touch the beans, you should grind those coffee beans before it’s too late.
  •  It is generally harder to tell with a lighter roast, you want the beans to have a shiny look however they shouldn’t be oily. You can also throw some roasted beans into a resealable plastic bag, pressing the air out and leaving it overnight. If the plastic resealable is puffed up there is still some CO2 being released. This shows that your beans are still pretty fresh.
  • The majority of coffee bean bags have valves, this will give you an indication to whether or not your coffee beans have finished degassing.


The Bloom Stage of Degassing

The last part of the degassing process happens in the brewing. The process of pre-infusing  your ground coffee enables the trapped CO2 that is left to escape to make sure that a full extraction is completed. This part of the process is called the Bloom and is triggered by the contact between beans to hot water.

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