The fresher the coffee, the better...right? Well, that's not entirely true.

There is no doubt that no one likes to drink expired coffee, but if you brew the roasted coffee beans directly, the flavor will definitely disappoint you. The reason is that the coffee is still in a state of venting a lot of gas at this time.

Whether you are a roaster or brewer, you must understand degassing. In this article, let’s understand what degassing is, how degassing affects the coffee you brew, and how to perform these actions.

2. What is exhaust?

Degassing is the process of releasing gas from coffee beans after roasting. When you roast coffee, a large amount of carbon dioxide and gas is produced inside the coffee beans.

A lot of gas will be released in the first few days after roasting. The problem is that these gases will release small bubbles when you brew, which will affect the coffee you brew. These bubbles will destroy the contact between the coffee powder and water, resulting in uneven extraction of flavor and aroma substances.

In other words, if you brew freshly roasted coffee, these gases will negatively affect the flavor of your coffee.

For this reason, it is a good idea to wait a few days after roasting before brewing the coffee. The period of time during which carbon dioxide is released and chemical changes occur is called degassing.

3. Why does coffee contain carbon dioxide?

When coffee is roasted between the first and second cracks, the beans will undergo a degradation reaction, and at about 220°C, the sugars will break down into several different compounds, including carbon dioxide. The beans will begin to turn brown because the water loss will also decrease.

The degradation reaction is the most important chemical reaction at the end of baking because when the degradation is converted into sugars, gas is produced when energy is released.

4. Exhaust to make coffee just right

But the carbon dioxide in coffee beans is not a bad thing, it plays an important role in the quality of coffee. The Journal of Agricultural and Food Chemistry in 2018 mentioned:

“Carbon dioxide is an important indicator of coffee freshness and plays an important role in shelf life and packaging. It affects the process of coffee extraction, the formation of espresso crema, and may also affect the sensory flavor characteristics of coffee.”

When coffee beans are over-vented, the flavor will be less distinct. The secret is to let the venting time be moderate, and not wait until the beans are too old and become old before using them.

5. How long does it take to exhaust?

Exhaust will disperse the carbon dioxide produced by the coffee during the roasting process, but we don't want these gases to disappear completely. Instead, we want the gas content of the coffee to be just right when we want to drink it. The right amount of carbon dioxide will make the coffee taste less bland.

But how long to keep the coffee beans after roasting depends on many factors. Usually, three days to two weeks or three weeks after roasting are suitable for brewing. However, the differences between each type of coffee will also make the required degassing time different. The brewing method, processing method, and roasting degree will affect the length of the degassing time.

The brewing method determines how long the bean-raising period is

If the coffee beans are for hand brewing or French press, they can be used up as soon as possible within a few days after roasting , because the coffee has a longer contact time with water, so there is no need to exhaust too much gas.

On the contrary, when we make espresso, because the brewing time is very short (usually only more than 20 seconds), it means that bubbles will affect the extraction results to a greater extent.

“Espresso is very special. It requires a longer bean-raising period. You won’t see people taking freshly roasted coffee and making espresso directly. The key is to raise the beans and exhaust the air so that the coffee can bring out its flavor when brewed.”

Coffee processing methods affect the growing period

The three main coffee processing methods: washed, natural, and honey processing, will also affect the degassing of coffee. Mark said: " We believe that natural coffee beans need a longer degassing period than washed ones. "

“If you brew natural beans three to five days after roasting, they are often too fresh. Natural beans need more time to degas.”

The degree of baking affects the exhaust time

Dark roasted coffee will accelerate the degassing of coffee beans because the coffee beans are more degraded. The sugars are converted to a greater extent and there are more small cracks that cause more carbon dioxide to be released.

“Light roasted coffee beans are closer to being unroasted, which means that lighter roasted coffee beans need more time to degas.”

Note: If the coffee beans are not roasted evenly, it may cause uneven development of the coffee bean substances; different degradation times will affect the degree of development of the coffee beans, and then affect the speed of exhaust of the roasted beans.

How to maintain the freshness of coffee beans

How can you make sure that the coffee beans have been properly grown before you drink it?

“It’s very helpful to keep accurate records of roast dates, especially when you’re roasting large quantities of beans.”

Use nitrogen to fill the coffee bean bag. With nitrogen, the shelf life of the coffee beans can be maintained longer.

It usually bags the coffee 20 minutes to an hour after roasting, but the premise is that the coffee bean bag must have a degassing valve . When customers receive our coffee, it is usually three days after roasting. The degassing valve is to allow the coffee beans to be properly degassed during transportation and prevent the bean bag from bursting if there is a collision.

The packaging bags of the "Star Story" specialty coffee beans in our store are all equipped with exhaust valves

The secret of exhaust and bean cultivation in home-baked coffee

It is recommended to roast the beans as soon as possible once the green bean storage tank is opened and leave it for four days. And use the natural circulation method so that the coffee is not roasted too much at a time, so that you can drink the best coffee. "Remember when the coffee beans were roasted, and consider that the storage space and brewing method will also affect the exhaust. The exhaust time required for each type of coffee bean is also different, and some will take longer to exhaust. If the flavor of the coffee is not as good as you expected, you can try to exhaust it for a few more days, but be careful not to let it become expired beans.

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I am Afei, I have been engaged in promoting coffee culture for more than 6 years. I have been to coffee farms in Indonesia, Yunnan, Taiwan, and coffee consuming cities in Italy, the Netherlands, Germany, and France. I love specialty coffee and want to make friends who love coffee as much as I do. Welcome everyone to follow my Toutiao account and my new book "Fall in Love with Coffee in 3 Minutes", where I will share and exchange knowledge about specialty coffee, latte art, and store opening. Love coffee, let's get together. Share a wonderful life with you every day.