Oily Coffee Beans: Why Are Some Coffee Beans Shiny?

That oily sheen on your coffee beans is entirely natural, but is it a good thing?

Today, we’ll be taking a look at what makes coffee beans oily, when you should be concerned about oily coffee beans, and what coffee equipment you can and can’t use with oily beans.

Why Are Some Coffee Beans Oily?

It’s all about the roasting process. All coffee beans start off green. During the first phase of the roast — drying — they turn yellow.

After that, they go from yellow to brown through the Maillard reaction, the same chemical reaction that gives toasted bread, seared steak, and toasted marshmallows their added flavor and brown coloring. 

Finally, coffee beans go through their first crack, which releases trapped gasses and oils from the beans. This is what makes coffee beans oily, and it doesn’t stop after the initial release. The type of roast makes all the difference in the oiliness of the beans.

Light roasts and medium roasts produce non-oily coffee beans. As beans are roasted darker, more oils continue to get out and make their way to the surface. Eventually, a dark roast will accumulate enough of an oily surface layer to have a noticeable sheen. 

So when you ask why is my coffee oily, the answer is probably the roast level. You may have just bought a darker roast than you are used to.

Are Oily Coffee Beans a Problem?

Not necessarily. The release of oils is a normal part of the roasting process, especially for particularly dark roasts. You may even find that some of your medium roasted beans have a light layer of oil — often not noticeable until you are handling them. 

However, oils continue to release after the roast process. If you come across a medium roast — or especially a light roast coffee — that is visibly oily, you should check the roast date and do a sniff test. An overabundance of oils —more than you would expect for the roast level — can be an indication that your coffee beans aren’t fresh.

Well, that’s true for light and medium roast coffee beans, but oily dark roasts actually go the other direction. Because the oils have already made their way to the surface, the beans dry out over time. Non-oily coffee beans may actually be a sign of stale coffee beans in dark roasts. Since some dark roasted coffee beans don’t start off oily, though, it’s still a good idea to check the roast date.

Are oily coffee beans bad for coffee makers?

They can be. Most coffee makers operate perfectly fine with oily coffee beans, but the oils can clog super-automatic espresso machines or grind-and-brew coffee makers, especially if they have a blade grinder.

Light and medium roasts — or less oily dark roasts — are the best coffee beans for automated espresso machines. Oily beans can leave a residue in the bean hoppers of these machines, clog their grinders, and possibly prevent the grounds from properly flowing through the machine.

You should also avoid using blade coffee grinders for oily coffee beans. Then again — as I mention every time I’m talking about how to grind coffee beans — blade grinders are terrible anyway. The best coffee grinder for oily beans just happens to be the same as the best grinder for any other coffee: a burr grinder. 

Can You Dry Oily Coffee Beans?

Not really. Removing oil from coffee beans will also get rid of all the flavor, destroying the quality of your brew. The oils in coffee beans are not a bad thing. When coffee beans get old, the oils are just an indicator of quality — a symptom — so removing them won’t do any good. And if you need dry coffee beans for your automated espresso machine, you are much better off buying a lighter roast than trying to figure out how to dry oily coffee beans.

What Do Oily Coffee Beans Taste Like?

The oiliness of the beans doesn’t change the taste of the coffee, but it can still indicate something about the flavor. As I mentioned earlier, darker roasts have more oil. Very dark beans — think French roasts and Italian roasts — are particularly oily.

Darker roasts have bolder flavors, but much of the sugar burns off during the roasting process. That’s why dark roasts have less of the sweetness, fruitiness, and complexity that you’ll find in lighter roasts. It’s harder to make out the flavors of the individual origins in darker roasts, but they are often preferred as espresso beans and in some other espresso-like brewing methods.

Darker roasts also have less caffeine than lighter roasts. Coffee drinkers often associate the bold flavor of a dark roast with the strength of caffeine, but that connection is actually misleading. Bold coffees come from darker beans, and darker beans have lost some of the caffeine they would have had as medium- or light-roasted coffee beans.

A Few Final Words

If your dark-roasted beans are shiny, there’s no reason to worry. Unless you have an automatic espresso maker, oily beans are perfectly fine. If you like especially dark roast coffees, you’ll probably be working with oily beans at some point. If you see extra oils on your light and medium roasts, though, it might be time to check them for staleness.

The oils in coffee beans are an important part of their natural flavor profile. But if you are tired of them getting all over your hands and equipment the answer is easy — get a lighter roast for your next cup of coffee.