- Oily coffee beans on a wooden spoon. Written Text “Why are Coffee Beans Oily?”

Why Are Coffee Beans Oily?

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You must have come across shiny-looking coffee beans and wondered why they are so oily. You even would have refrained from using them, thinking they have gone bad. However, oily coffee beans do not necessarily mean there is something wrong with them.

Coffee beans are oily because the cellulose structure breaks down during roasting. The outer layer becomes porous and the lipids inside escape to the outer surface of the coffee beans. Dark roast coffee beans are more oily as they have been heated for longer in comparison to light and medium roasts.

Why Are Coffee Beans Shiny And Oily?

Before answering that question, you should know that coffee beans are not brown in their natural state. In fact, coffee beans are cherry-like small beans that are roasted. In their natural state, coffee beans are green.

The green coffee beans change drastically when they are heated/roasted. The greenish beans turn brown, and oil appears on the surface of the beans. These oils, however, are not just the byproducts of the roasting process but have effects on the taste and aroma of the coffee too.

How Does The Roasting Process Occur?

Despite their unassuming appearance, green, raw coffee beans are high in carbs, amino acids, moisture, caffeine, and lipids. Each of these components reacts uniquely to heat during a roast, resulting in various alterations in the beans. The reactions of these components lead to the formation of oils on the surface.

Heat weakens the endosperm and renders the outermost part or outer layer of the bean more porous. Hence, a lot of tiny openings form on the bean allowing oils deep within the bean’s structure to rise to the topmost/outer layer.

As underlying layers in the bean start breaking down, more oils surface as the roast progresses. The longer the coffee beans are roasted, the oilier it gets. As a result, dark roasted coffee beans have a higher oil content than lightly roasted coffee.

Coffee beans being roasted in a roaster

Why Are Some Roasted Coffee Beans Dry And Some Oily?

As discussed above, when the cellulose structure of the green coffee beans breaks down, the lipid layer inside releases its oils. Since dark roast coffee beans are roasted for longer, they are more oily. Medium roast coffee beans are moderately oily, while light roast coffee beans are the least oily.

After the roasting process, the beans are exposed to oxidation. When the oil on the surface of the coffee beans reacts with oxygen in the air, it results in the formation of peroxide. Therefore, more peroxide is formed when beans are left outside without a proper container for a long time. Thus, the taste of the resulting brew is affected. This effect is more prominent in dark roast coffee beans, so you should consume it sooner to prevent unpleasant tastes even if you have stored it properly.

Comparison Of The Three Different Roast Types And Their Oil Level
Roast TypeTasteAromaColorOil ContentRoasting Time
Dark RoastBoldBitter and smoky smellDark BrownVery oily30 minutes
Medium RoastBalanced flavorSweet smellMedium brownModerately oily15-16 minutes
Light RoastLight and mild flavorFruit smellLight brownLeast oily8-9 minutes

Is It Safe To Drink Oily Dark Roast Coffee?

While there are no health consequences of drinking oily coffee beans, Healthline says that light roast coffee (less oily) contains a higher amount of antioxidants and polyphenols. Dark roast coffee beans lose a lot of compounds when they are roasted.

Why Are Starbucks Coffee Beans Oily?

If you have tried Starbucks coffee beans, you probably would have asked yourself, ‘Why are Starbucks coffee beans oily if it is such a renowned brand?’. Well, their oily beans do not mean that they are stale or old. It just means that the coffee beans are dark roasted!

Starbucks is known for roasting its coffee beans for prolonged periods, and that is why they are so oily. If you have gotten a pack of Starbucks coffee beans recently, we advise that you consume them as fast as you can to get the original aroma and taste because even Starbucks coffee can oxidize.

Does Oil Affect The Resulting Brew?

There is no straight answer to this question. In fact, there are conflicting opinions about this. Some may argue that the oil means that a coffee bean is fresh, while others say that the oil represents the coffee has gotten old. However, you can make a few assumptions about coffee by looking at its oil.

Oil on the coffee is not always a good thing and not always a bad thing either. Oily coffee beans (dark roasts) are often used to make espresso because oil makes better crema in the espresso. Even when the dark roasts are oily, they give a bold flavor. However, when there is too much oil on a medium and light roast, the aroma of the beans lessens, and the resulting coffee ends up tasting rather stale.

As discussed already, dark roasted coffee beans tend to have a greater oil content than medium and light roasts since they have been heated longer. Therefore, seeing oil on dark roast coffee beans is very normal. The oil on dark roast beans does not mean that the coffee is old and will taste fresh when brewed.

Too much oil on a medium roast coffee bean means that it has been in storage for quite some time. If you know that the coffee was not stored for a long time, it was probably not stored correctly, resulting in oil formation. Moderate oil on medium roasts is also normal. It could mean that the coffee beans were stored for a slightly longer time.

Oil on light roast coffee beans is not very normal, though. Since light roast beans were not heated for so long, seeing too much oil on them means the coffee beans have gotten either very old or have been in very improper storage. Keep in mind that any coffee left in improper storage for a long time will eventually lose its aroma and rich taste. As a general rule of thumb, avoid coffee that has gotten too old.

Why Oily Coffee Beans Are Bad For Grinders?

For automatic coffee makers, burr grinders, and espresso machines, oily beans might be a concern. The major issue with oily coffee beans is that they clog burr grinders and other parts of the espresso machine. They can also stick to the sidewalls of the bean hopper in your grinder. 

Whether it’s the inbuilt grinder of your coffee machine or a separate one, oily coffee beans can be a menace for them. Therefore, avoid greasy and flavored beans if you want to extend the life of your espresso machine and not have to go through regular grinder cleaning.

If you think you can tackle the problem by drying the beans, do not try! You can’t dry highly oily beans without altering the taste, so try to avoid them altogether. Oil is naturally present in coffee beans so when you try to wash and dry it, you end up washing away the taste and aroma.

 Oily coffee beans in a coffee grinder

How Can I Avoid Oily Coffee Beans?

Remember that these methods merely help to slow down the oxidation process, and coffee beans will eventually get oily over time, so do not use beans that have been sitting around for ages.

Switching To Medium/Light Roasts

The easiest way around it is to switch to medium and light roast coffee beans as they have lesser oil content.

Proper Storage

Whether you are using dark, medium, or lightly roasted coffee, the key is to store them properly. Use airtight containers to store your coffee beans. Airtight containers minimize the interaction of coffee beans with oxygen in the air and thus prevent oxidation. When oxidation does not occur quickly, the beans can be used for longer durations without a stale and bitter taste in them.

Experiment With The Brew

We know that some of you prefer dark roast coffee beans because of the bold taste. However, you can switch to light and medium roast beans and still achieve that bold flavor! Just grind your light or medium roast coffee beans finer into a powder, and the resulting brew will have a very bold taste.

You can also get a bold taste by reducing the water in the brew when using a light or medium roast. If that doesn’t do the trick, then reduce the water and increase the amount of light and medium roast for an even bolder taste. You can experiment with the quantities and get bold, rich coffee (similar to dark roast) without damaging your grinder!


Why are coffee beans oily? Well, oil has always been within them! The longer they roast, the oilier the coffee. We discussed the different implications of oily coffee and the entire roasting process and even taught you how to get around the oily coffee beans problem. We hope this was helpful and you know more about storing and preserving your coffee now.

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