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What is the purpose of the exhaust valve on coffee bags? Can you squeeze it to smell the aroma?

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, Squeeze it, pinch it, and so much fragrance will spray out. Many people may have observed that when customers purchase coffee beans, they will first put their nose close to the only hole in the packaging bag, squeeze the bean bag with their hand, and smell the gas squeezed out from the hole. Have you read "Why doesn't coffee taste as good as it smells?"

Squeeze it gently, and you'll see so much aroma being released from it.

Many people may have observed that when customers select coffee beans, they first bring their nose close to the unique hole in the packaging bag, squeeze the bean bag with their hand, and smell the gas squeezed out from the hole.

Those who have read the article "Why doesn't coffee taste as fragrant as it smells???" should immediately realize that's right! This gas is precisely the carbon dioxide and volatile aroma emitted by coffee beans. It's truly fragrant!! That's why people often squeeze it when they take it home, take a sniff before brewing coffee, and feel absolutely wonderful.

HOWEVER!!! Although this hole is for degassing, it's not meant for squeezing and smelling the aroma.

The Purpose of the Hole

This hole is actually a valve device called a "one-way degassing valve." Like a one-way street for cars, gas can only exit from one direction and cannot enter from the other direction.

When coffee beans are freshly roasted, their bodies contain large amounts of carbon dioxide, which will be emitted in large quantities over the next few days. However, after the coffee beans cool down from roasting, we immediately pack them into sealed bags. Without a one-way degassing valve, the large amount of carbon dioxide emitted would fill the entire bean bag, and when the bag can no longer support the continuous gas emission from the beans, it would easily burst.

With a degassing valve, when the bag is filled with gas and the beans emit new gas, the internal pressure becomes higher than the external pressure. This pushes open the valve and releases excess gas outward. Once the excess gas is completely released and pressure returns to normal, the valve returns to its closed state. Therefore, the one-way degassing valve has only one simple function: "preventing gas from bursting the packaging bag."

The use of a one-way degassing valve allows coffee beans to be stored in an almost airtight space. The release of carbon dioxide carries with it the volatile aroma of the coffee beans themselves. When coffee beans come into contact with air, it will accelerate the emission of carbon dioxide, causing the loss of large amounts of aromatic compounds. However, due to packaging limitations that cannot withstand too much internal pressure, a one-way degassing valve was specifically designed to allow gas to exit but not enter.

Why Squeezing the Bean Bag to Smell the Aroma is Not Recommended

This is because when the gas inside the bean bag reaches saturation, it can inhibit the rate at which coffee beans emit gas, making the degassing process slow and effectively extending the flavor window. When you artificially squeeze the gas out of the bean bag, the pressure inside will create some difference with the outside world. As you can see, its design is to solve the problem of fresh beans emitting large amounts of gas in the first few days after roasting, which could burst the coffee bag during transportation.

So, if you want to extend the flavor window, besides not squeezing the bean bag, you can also choose to use adhesive items like stickers to seal the degassing valve;

Alternatively, you can transfer opened coffee beans to a sealed container. These methods can effectively reduce the degassing rate of the beans and extend the optimal flavor window of coffee beans.