What's the Purpose of the Ventilation Holes on Coffee Bean Bags? What is a One-Way Degassing Valve? What Are the Differences in Coffee Bean Bag Materials?

The One-Way Degassing Valve in Coffee Bean Packaging

Most coffee beans on the market are packaged in bags, and on these bags, we often notice several small holes that appear to have been pierced by a needle. Behind these holes lies a simple degassing device.

The "one-way degassing valve" is the name of this device, and its function is exactly as its name suggests - gas can only escape in one direction and cannot enter from the opposite direction. FrontStreet Coffee often uses an analogy to describe this: "a one-way street for cars" ~ So why do coffee bean packaging bags need such a device?

Why Use a One-Way Degassing Valve?

At this point, clever friends might chime in: To smell the aroma!!!!

Although this opening indeed serves such a purpose, it is not its primary function, nor was it the reason people developed it. Its true function, its true purpose, is only one - to prevent coffee bean bags from exploding!!

As we all know, coffee beans accumulate a significant amount of carbon dioxide due to chemical reactions during the roasting process. Initially, this carbon dioxide is trapped inside the coffee beans due to pressure. However, as roasting completes and the beans cool, these gases begin to escape. Because the aromatic compounds in coffee beans are volatile, they continuously evaporate, especially when exposed to oxygen, which accelerates the release process. Therefore, we need to immediately seal coffee beans in airtight containers after roasting to reduce oxidation caused by oxygen intrusion, allowing the flavor to be preserved longer.

However, this presents a problem. Within the first week after roasting, nearly 70% of the carbon dioxide in coffee beans is released - a considerable volume of gas. This is particularly true when coffee beans are roasted darker, as they contain more carbon dioxide and release more, as demonstrated in the image below. (Left: dark roast beans, right: light roast beans)

Coffee beans crack during roasting when they can no longer withstand the continuous accumulation of internal steam, and the same happens with sealed coffee packaging bags. While most sealed bags can withstand the continuous filling of carbon dioxide, with just a slight external pressure or when opening the bag, Boom!!! The carbon dioxide will burst out at once, directly causing the bag to explode. Because dark roast was the mainstream roasting level in the last century, roasters at that time faced significant challenges. They tried various methods to deal with this large amount of carbon dioxide released in a short period. For example: replacing sealed bags with harder bags or sealed containers; pre-degassing coffee beans before bagging and sealing them.

However, without exception, these methods were not widely adopted due to certain drawbacks. For example, pre-degassing requires too much time and is difficult to measure, which would accelerate the oxidation of coffee beans and cause more intense loss of flavor compounds, resulting in completely negative effects. If sealed bags were replaced with harder material bags or sealed containers, it would lead to excessively high costs, basically 3-4 times the original cost. So after many attempts, they ultimately returned to using bags. It wasn't until 1960 that an Italian packaging company introduced a one-way degassing valve and registered a patent, finally breaking this awkward situation.

The composition of a one-way degassing valve is quite simple: a plastic shell with holes for degassing and a rubber diaphragm - that's it. The principle of one-way degassing is equally simple to understand: The valve initially remains in a closed state because the rubber valve piece blocks the holes. When internal and external pressures are equal, gas cannot escape from inside, and external gas cannot enter. As the coffee beans in the bag continuously release gas, the bag gradually fills with gas, and pressure increases. Until the gas releases to the point where internal pressure exceeds external pressure, this rubber valve piece is pushed open, allowing gas to escape outward. When excess gas has been released and internal pressure returns to normal, this rubber valve piece returns to its original shape, and the degassing valve returns to its closed state.

In summary, we can see that the purpose of the one-way degassing valve is truly only one: "to prevent gas from bursting the packaging bag." The reason we can smell the aroma by squeezing the bean bag through the degassing valve is precisely because, besides carbon dioxide, aromatic compounds are also continuously evaporating. Therefore, the gas squeezed out contains not only carbon dioxide but also the aromatic compounds evaporated from the coffee. Although it claims to be sealed, if you purchase too many coffee beans and cannot finish them in a short time, FrontStreet Coffee still recommends using stickers to seal these holes to prevent gas leakage~ Also, for those who squeeze to smell the aroma, stop squeezing!!

Important Notice :

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