Are Swollen Coffee Beans Safe to Drink? Why Do Coffee Beans Expand and Release Gas?

Understanding Coffee Bean Bag Swelling: Is It Spoilage?

"Boss, why is this bag of coffee beans so swollen? Has it gone bad?" a friend asked, looking at a bag of coffee at FrontStreet Coffee that had expanded to twice its normal size.

It's understandable to have such suspicions. After all, in daily life, when packaged food suddenly shows signs of swelling, it's likely caused by the growth of mold or bacteria producing gas, resulting in what we commonly call spoilage. Coffee beans can also experience similar spoilage when stored improperly. However, when coffee beans spoil, they typically exhibit strong characteristics of moldy, sour, or putrid odors, just like other spoiled foods. If you don't detect similar smells on the coffee beans, then the swelling is most likely caused by the "degassing" phenomenon that occurs after coffee beans are roasted.

The Degassing Phenomenon of Coffee Beans

During the roasting process, coffee beans continuously undergo Maillard reactions and caramelization. These chemical reactions cause the continuous decomposition and restructuring of organic compounds within the coffee beans. As organic compounds decompose, they generate large amounts of carbon dioxide and other volatile gases. These gases continue to be released from the coffee beans after roasting is complete, especially within the first 72 hours when degassing is most intense. These gases are the "culprits" behind coffee bag swelling.

However, under normal circumstances, causing significant swelling of coffee bags isn't a simple matter. This is because most manufacturers use bags with one-way degassing valves for packaging to ensure coffee beans don't burst during transportation. Since FrontStreet Coffee has several articles specifically introducing one-way degassing valves, we'll just briefly explain them here. Their function is somewhat similar to a one-way street, allowing gases to escape from inside the packaging while preventing oxygen from entering from outside. This ensures that coffee bags won't be burst by carbon dioxide while also preventing excessive oxidation of the coffee beans due to too much contact with oxygen.

So generally, coffee bags don't swell easily. For example, among the dozens of coffee beans displayed on FrontStreet Coffee's shelves, the vast majority show no signs of swelling. This brings up the question: why do some still swell?

The answer is simple! Because the coffee beans release gas too vigorously in a short period, far exceeding what the one-way valve can release quickly, causing the bag to swell. This situation is typically caused by extremely dark roasted coffee beans. For example, the customer friend mentioned at the beginning of FrontStreet Coffee was looking at a bag of dark roasted Golden Mandheling.

The amount of carbon dioxide in coffee beans is affected by the degree of roasting. When coffee beans are roasted darker, more Maillard reactions and caramelization occur, naturally producing more carbon dioxide. Additionally, dark roasting causes more expansion and rupture of the coffee beans' cellular structure, making it easier for gases to escape from within. These two reasons together cause coffee beans to release large amounts of gas in a short period, leading to bag swelling. (The sealed one on the left is freshly roasted dark beans, the sealed one on the right is freshly roasted light beans)

Conclusion

In summary, we can determine that coffee bag swelling is a normal phenomenon. It's not because of spoilage or staleness (though possible, but unlikely), but rather occurs when coffee beans are roasted too dark or when the packaging bag doesn't have a one-way degassing valve.

Important Notice :

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