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Can You Still Drink Clumped Coffee Powder? How to Store Coffee Powder to Prevent Clumping?

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, Coffee powder clumping is a common issue that many coffee lovers encounter during the brewing process. If the clumped coffee powder is within its expiration date, it is still drinkable. However, if the coffee powder is both clumped and moldy, it has mostly spoiled and is not suitable for consumption. Reasons for coffee powder clumping: 1. Heat-induced clumping - Coffee beans contain

Regarding the phenomenon of coffee beans appearing oily on the surface, FrontStreet Coffee has noticed that coffee beginners have various questions:

"Why are the coffee beans wet? They're newly opened"

"The coffee beans are all oily, they must have been sitting around for a long time"

"The coffee beans are so oily on the surface, could they be spoiled?"

The "oil" on the surface of coffee beans is essentially the bean's water-soluble fat.

Before roasting, green beans have a tight cellular structure, with oils encapsulated within the fiber matrix. During the roasting process, the roaster provides significant thermal energy to the coffee beans, causing the internal structure to continuously expand. This further opens the pores in the cell walls of the green beans, which store large amounts of carbon dioxide. As the roasting depth increases, when roasting is complete and the coffee beans return to normal temperature and pressure, these carbon dioxide gases begin to slowly release, simultaneously allowing fats to seep through and adhere to the bean surface.

The Impact of Roast Level

Oily appearance generally manifests in coffee beans roasted to dark roast level or above, that is, around the second crack, when oils gradually seep to the surface along with the gases. Freshly roasted dark beans will show a slight sheen of oil. By the second day, carbon dioxide begins to release more rapidly, while emitting roasted aromas of caramel, dark chocolate, and more.

For example, FrontStreet Coffee's Indonesian Golden Mandheling coffee beans are roasted to medium-dark level and will develop an oily sheen after 3-5 days of resting, which is a normal phenomenon. During the optimal tasting period, some coffee beans 5-7 days after roasting may develop droplet-shaped oils on the surface. This phenomenon occurs due to uneven heating causing localized dehydration, and these droplet-shaped oils precisely represent the coffee's optimal tasting period.

Therefore, oiliness is simply one criterion for judging the roast level of coffee beans and has no necessary relationship with freshness. For extremely dark roasts like "Japanese-style dark roast coffee," the beans may start showing oil on the first day after roasting while still in the packaging, and soon the coffee beans will appear dark and glossy.

Signs of Moisture-Damaged Coffee Beans

If coffee beans have been exposed to moisture, they generally won't appear "wet" on the surface, and it's difficult for us to determine directly by sight whether roasted beans have been moisture-damaged. However, we can make judgments based on signs that appear during the brewing process.

Freshly roasted coffee beans have very low moisture content, approximately 1-2%. If stored in a humid environment, coffee beans act as moisture absorbers, leading to increased water content and subsequent spoilage and mold growth. Common phenomena include grinding difficulties, clumping of coffee grounds, loss of aroma, and appearance of musty odors.

How to Determine if Coffee Beans Are Fresh?

The most common packaging for coffee beans includes one-way degassing valve sealed bags and vacuum-sealed containers, which can isolate coffee beans from water molecules in the air. Additionally, the carbon dioxide they release themselves acts as a protective gas, enveloping the coffee beans and thereby slowing the dissipation of coffee flavors. Once the packaging is opened, the oils will contact moisture in the air and undergo oxidation, accelerating the aging of coffee beans.

When some light to medium roast coffee beans are stored for a period of time and the entire surface develops a layer of oil, smells weak in aroma, and carries a slightly greasy smell, this indicates that a significant portion of the flavor has already dissipated, and they should be consumed as soon as possible.

Freshness is most apparent during the extraction process. For example, during blooming, if the coffee bed shows no expansion at all, it indicates that the gases in the coffee beans have been completely released. Throughout the entire extraction process, no aroma is released, the flavor is empty, and it tastes woody and fibrous.

The main factors affecting coffee bean freshness include oxygen, moisture, light, and heat. Therefore, to properly store coffee beans, one needs to ensure they remain unground, sealed, protected from light, moisture-proof, and kept at low temperatures. Even with these conditions met, the flavor of coffee beans will gradually dissipate over time. Therefore, compared to long-term storage, FrontStreet Coffee still recommends enjoying them during their optimal tasting period.