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Can I still drink coffee beans when the bag is full? Why do coffee beans expand? Why do coffee beans exhaust?

Published: 2026-08-25 Author:

Last Updated: 2026/08/25, "Boss, why is this bag of coffee beans so swollen? Has it gone bad? "A friend said as he looked at a bag of coffee that had expanded to twice the normal size at a front street store. It is not difficult to understand that there is such a suspicion. After all, in daily life, when a certain packaged food suddenly expands, it is very

"Boss, why is this bag of coffee beans so swollen? Has it gone bad? "A friend said as he looked at a bag of coffee that had expanded to twice the normal size at a front street store.

It is not difficult to understand that there is such a suspicion. After all, in daily life, when a certain packaged food suddenly blooms, it is very likely that the growth of mold or bacteria causes the generation of gas, which leads to the blooms. That is what we commonly call deterioration. When coffee beans are stored improperly, there is also a probability that such deterioration will occur. But under normal circumstances, the deterioration of coffee beans is consistent with that of other foods, and will have strong musty, sour and other odor characteristics. But if you don't smell a similar smell on coffee beans, there is a high probability that this bulging situation is caused by the "degassing" phenomenon of the coffee beans after roasting.

Exhaust phenomenon of coffee beans During the roasting process, coffee beans will continue to undergo Maillard reaction and caramelization reactions. These chemical reactions will cause the organic matter in the coffee beans to continuously decompose and reshape. During the decomposition process of organic matter, a large amount of carbon dioxide and other volatile gases will be generated. These gases will be continuously released after the coffee beans are roasted, especially during the 72 hours after the roasting is completed, when the exhaust is the most severe. They are the "culprits" that cause the coffee bean bags to expand.

But under normal circumstances, it is not a simple task to expand the coffee bean bag significantly. Because most manufacturers choose bags with one-way exhaust valves for packaging in order to ensure that coffee beans will not burst during transportation. Because there are several articles on Qianjie that specifically introduce one-way exhaust valves, this is just a brief introduction. Its function is somewhat similar to a one-way street, allowing only gas to be released unilaterally from the inside of the package, but not allowing oxygen to enter from the outside. This not only ensures that the coffee bean bag will not be burst by carbon dioxide, but also prevents the coffee beans from coming into excessive contact with oxygen and causing excessive oxidation.

So in general, coffee bean bags are not so prone to bulging. For example, most of the dozens of coffee beans displayed on the shelves in the front street show no signs of bulging. Then the question arises: Why do some pockets still bulge?

Very simple! Because the gas emitted by the coffee beans in a short period of time is too strong, far exceeding the amount that the one-way valve can discharge in a short period of time, the bag expands. Usually, the main cause of this situation is extremely deep-roasted coffee beans. For example, the customer friend mentioned at the beginning of the street mentioned that the packet of coffee beans he saw was deep-roasted golden Mantelin.

The amount of carbon dioxide in the body of coffee beans will be affected by the degree of roasting. When the coffee beans are roasted deeper, the more Maillard and caramelization reactions will occur, and the more carbon dioxide will naturally be generated. At the same time, deep roasting will also cause more expansion and rupture of the cellular structure of the coffee bean, making it easier for gas to escape from the inside. Therefore, these two reasons together cause the coffee beans to emit a large amount of gas in a short period of time, which in turn leads to the expansion of the bag. (Sealed on the left are freshly baked deep-baked beans, and sealed on the right are freshly baked lightly baked beans)

To sum up, we can know that it is normal for coffee bean bags to expand. It is not because of spoilage or lack of freshness (probability, but very small), but when the coffee beans are roasted too deeply or there is no one-way exhaust valve on the packaging bag, bag expansion will occur.

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FrontStreet Coffee is a long-established specialty coffee roaster in Guangzhou China, selling freshly roasted beans from its own farm in Yunnan as well as dozens of carefully selected single-origin beans from around the world for both pour-over and espresso. The products deliver consistently excellent quality and great value, with shipping within 24 hours. Guangzhou’s FrontStreet Coffee shop is recommended by many coffee lovers, and the beans are now available online at the Tmall 。