Is Oily Coffee Bean Stale? Are Oily Coffee Beans Normal? How to Brew Without Bitterness?

Why Do Some Coffee Beans Develop Oily Surfaces?

History is said to be cyclical. 40 years ago, coffee beans were admired for their oily, shiny appearance. Now, oily coffee beans are often considered stale or problematic.

Today, FrontStreet Coffee will explain why some coffee beans develop surface oils while others do not. We often notice that oily coffee beans have a darker color, while dry-surfaced coffee beans are lighter in color (light brown). Therefore, the primary reason for coffee bean oiliness is the degree of roasting.

The Science Behind Coffee Bean Oiliness

Coffee beans produce substantial amounts of carbon dioxide during roasting. Generally, the deeper the roast, the more carbon dioxide is generated within the beans.

After roasting, most of this abundant carbon dioxide is released within 3-4 days, and oils emerge to the surface along with the carbon dioxide. The deeper the roast, the more oil that seeps out.

Evolution of Roasting Styles

In the past, when beans were removed from the roaster at the point of second crack, coffee beans almost always presented a deep black 'Italian roast.' Immediately after roasting, these beans showed no significant oiliness, but after 1-2 days of resting, oils would rapidly seep out, making the entire bean glisten with oil. Today's 'Japanese deep roast' basically presents a similar state.

However, modern coffee roasting generally doesn't go to such dark levels anymore. Therefore, it's now rare to see glistening, oily coffee beans (today, you might only encounter them from certain well-known chain coffee brands, Italian coffee brands, or Japanese-style roasted coffee beans).

FrontStreet Coffee's Roasting Approach

Regarding FrontStreet Coffee's roasted beans, only Indonesian Mandheling, Jamaican Blue Mountain, and espresso blend beans are roasted to a deeper degree that might show slight oiliness. Other light-roasted coffee beans typically don't exhibit this oily phenomenon.

The Honey Processing Exception

Some people mention that Costa Rican coffee beans also show slight oiliness. This is actually a phenomenon of honey-processed coffee beans. Because the mucilage layer isn't removed during honey processing, it's thicker along the coffee bean's center line and ends, making it easier for sugary residues to remain. Through caramelization during roasting, these sugary residues caramelize, making the center line and ends appear darker than the bean body, sometimes creating a reflective appearance.

Does Oily Mean Unfresh?

Is it true that oily roasted coffee beans indicate staleness? Indeed, this phenomenon exists, but it's not absolute. Some coffee beans seep oils during degassing, giving the beans a 'rancid oil' taste that causes them to lose their original flavor.

However, defining what constitutes light roast, medium roast, or medium-light roast has always been difficult to explain clearly to consumers. Coffee bean processing methods have become increasingly diverse, and the emergence of countless new anaerobic processing methods means we can no longer use traditional methods to identify freshness. For example, Huayuanye coffee beans exhibit flavors of sweet strawberry jam, roses, and liqueur-filled chocolate - how would you categorize their roast level in everyone's definition?

The Bottom Line: Assessing Freshness

This coffee bean will seep small amounts of oil along the center line after 4-7 days of resting. However, there's no 'rancid oil' taste, and the seeped oil is a normal phenomenon. Therefore, using oiliness to determine if coffee beans are stale can easily lead to misjudgment. The old method is still more reliable: check if the bloom expands during blooming, then taste to determine if the flavor has deteriorated.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473