The Truth About Oily Espresso Beans? Great Or Disastrous?

You might have noticed that the beans you’ve been buying to make your morning espresso with are oily. It that a good or a bad thing and why does that happen?

Beans being oily doesn’t make them good for espresso. In general, espresso is made with dark roasted beans which can be oily on the outside. Dark roasted beans are what create the typical espresso taste but can be problematic for some grinders and automatic espresso machines.

What makes coffee beans oily and how can you keep your machine in best shape? Find out below.

Should Espresso Beans Be Oily?

You’ve heard beans that are good for espresso are oily. Is that actually true?

Just having an oily exterior is not what makes beans good for espresso. The oily exterior is an indicator of a dark roast which is often used for espresso and is largely responsible for the typical intensely bitter espresso taste. However, it’s possible to make great espresso without the beans being oily.

Oily beans are roasted dark and darkly roasted beans are often used for espresso. That’s for a few reasons:

• Darker roasted beans are easier to extract: To make espresso, you have to extract the grounds with little water and in a short amount of time. Because with a dark roast the cell walls are broken down already, it’s much easier for the water to extract the grounds than with lighter roasts.
• Dark roasts create the typical espresso taste: The darker the roast, the more bitter notes you get in your coffee. This creates the intensely bitter taste of espresso most people know and expect. However, darker roasts tend to have a little less caffeine.

The traditional Italian espresso is made with dark roasted beans. In the last years, many espresso aficionados have actually moved towards using lighter roasts. This is because lighter roasts can produce a more balanced espresso with less harsh bitterness and more sweet notes. This brings its own set of challenges though. However, dark roasts don’t have to be oily and oily beans doesn’t mean they’re good for espresso.

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Note: On darkly roasted oily coffee beans the oil is exposed to oxygen. The oil is where a lot of the taste of espresso actually comes from. Exposed oils can oxidize and go rancid much faster than when they are contained. That means dark roasted beans actually deteriorated much faster than lighter roasted beans.  

Are Oily Beans Problematic For Espresso?

Oily beans can actually be problematic for making espresso but not necessarily the taste. Although I personally don’t like espresso from oily beans because they tend to be way too dark for my taste, your taste might differ.

The problem is with your coffee grinder. Whether that’s a built in grinder or a separate one, oily beans aren’t very good for them. In non-oily beans, the oil is still contained within the cells of the coffee bean. On oily beans it’s leaking out of the cells. This is a problem because that means with oily beans, grinding can make a kind of paste that sticks to everything and gums up the burrs of your grinder.

After that the grinder doesn’t work properly anymore since all the ‘teeth’ are covered in coffee paste. It can also overheat the motor if the paste is gumming up the moving parts.

This happens to some degree with non-oily beans as well but much slower. Once everything is gummed up, you’ll have to take the grinder apart and clean it. This can take quite some time, sweat and swearing.

Once the coffee grounds are in the portafilter, oily beans aren’t really a concern anymore.

Why Are Some Coffee Beans Oily?

You might have noticed that some beans are oily and others aren’t. Before we get into espresso, it’s good to know why some beans are oily in the first place.

The reason coffee beans are sometimes oily on the outside is because they are roasted dark. Every coffee bean has oil inside of it. It’s usually contained within the cells. Coffee beans have cellulose cells that contain all the oils and other compounds. What happens when you roast the beans is that the cell walls of the cellulose break down and the oils escape. That shows up as a shiny oily surface on the outside of the beans.

If this happens depends on how darkly the beans are roasted. There is a very wide range of roast levels and not all roasts are oily. Since it happens because of the breakdown of the cellulose, the darker the roast, the more oil you tend to have. But, there are some differences in how quickly those oils are released and evaporate.

The oils will evaporate over time so if you have beans that were oily and aren’t anymore, they’ve probably gone stale. Also, on some beans the oil appears a few days after roasting and not immediately since it takes a while for the oils to make its way to the surface of the bean.

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Can You Use Light Roasted Beans To Make Espresso?

If your machine is having trouble with the oily beans, can you use a lighter roast to make espresso? Using lighter roasts to make espresso is not only possible but has become quite popular over the last years. The traditional Italian espresso is made with dark roasted beans, however many of the third wave coffee shops actually use lighter roasts.

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So it’s absolutely possible to do and actually has good results. You might get slightly different tasting espresso than with the traditional dark roast. If that’s to your liking is up to you. There will be slightly less bitterness and more balance in the espresso. Lighter roasts are known for having more aroma and a more floral character and when brewed often have a bit more depth of flavor.

There are some things to know about using a lighter roast to make espresso:

• Lighter roasts are harder to extract: Because the cells walls are more intact on lighter roasts, what’s inside those cells is harder to get out. You’ll have to grind a little bit finer than you would dark roasts. Hotter water will also help but this is hard to control on many domestic espresso makers.
• You don’t have to go all the way to light. If you just want to avoid machine troubles, a medium roast will work well. Medium to medium-dark will usually not have an oily surface but will still have much of the bitterness you like in espresso although it’ll be a little more subdued and balanced.
• Use slightly less grounds: Because it takes more work to extract lighter roasts, it could mean you under extract the grounds if you use the same amount of coffee grounds. If your espresso is coming out too sour and already adjusted the grind size, try using slightly less grounds (adjust by +- gram at a time) can help. Because you use less coffee but the same amount of water, that water has to extract less grounds leading to a higher extraction of the used grounds.