If you've noticed that your coffee beans are getting oily and aren't sure what to do with them, we're here to help.
Here, we'll provide you with everything you need to know, from why coffee beans are oily to how much oil they should have, whether they're good for grinding, and more.
Why Are Some Coffee Beans Oily?
As coffee beans have lipid content, the lipids within the bean can come to the surface in the form of an oil. This doesn't happen in the coffee cherries but instead occurs during a long roast or gradually when beans are stored after roasting.
Here's how coffee beans become oily from the coffee roasting process:
When you're roasting coffee beans, the steam from the water increases the internal pressure, which causes the beans to turn brown.
This specific reaction is called the Maillard reaction  and is due to an interaction between amino acids and sugars.
During this time, the structure of the beans will start to break, causing a snapping sound, also known as the "first crack.".
From there, the sugars caramelize, and the flavors of the bean will start to change.
As the coffee keeps roasting, the deeper structures will start to break down - also known as the second crack, while causing the outer shells to be more porous. With that, the coffee oil starts to ascend to the surface.
Oil On Fresh Coffee Beans
If you've noticed an oily sheen on fresh darker roasted beans, you'll be glad to know that it's quite normal and not necessarily of bad quality. As dark coffee beans already come with a good amount of oils, the roasting process simply brings this further to the surface.
On the other hand, light roast and medium roast coffee beans are less likely to look oily as the lighter roast hasn't been roasted long enough to draw the coffee oils out - unless they've been over roasted, of course.
So, if you've noticed oil on those fresh coffee beans, it's likely that the beans are old and no longer fresh.
Oil On Older Coffee Beans
As coffee beans age, the oils will naturally make their way to the surface. This takes a while, so if you've noticed a medium or light roast having an oily finish, it means that the beans are getting old and are starting to lose their flavor and quality.
If it has been a few weeks, however, you can still brew a cup of coffee with these beans. Just know that the coffee will have a slightly dark taste, so whether or not you like it all boils down to personal preference.
Past that, the aroma will be gone and you'll be left with a bitter coffee.
How Oily Beans Impact Coffee Characteristics
Here’s how oily beans go about impacting coffee characteristics:
Taste & Flavor
If you're constantly using oily beans in your coffee machine, the oils will build up in the machine, and this will result in foul tasting coffee. With that, the flavor of the coffee will no longer be fresh, and instead, you'll be drinking rancid coffee that's sure to leave an unpleasant aftertaste.
At the same time, leaving oily beans exposed for a long period of time will also cause the development of an unpleasant flavor, which will affect the taste of your coffee.
If you've got oily beans that have been roasted properly, however, you could end up with lovely coffee roasts that can be used to make a cup of dark roasted coffee that tastes great.
As mentioned earlier, when you roast coffee beans, it causes the development of oils on the surface. When the roast ends, however, the coffee beans are subject to oxidation.
When oily beans come into contact with oxygen, prolonged exposure from the surrounding air will turn the lipids into peroxide and cause the beans to become rancid. While this can happen with any roasted coffee, it happens much quicker with oily coffee beans.
What this means is that you'll want to consume darker roasts quicker than lighter roasts as they won't last as long. Otherwise, just store your darker roasts properly in a cool, dark place to maintain the freshness, and you'll be good to go. Remember, the taste of your coffee depends on this!
Problems With Oily Coffee Beans Vs Dry?
Ever wondered how oily coffee beans can cause problems? Well, one of their main problems is leaving an oily residue on the components of your espresso machine. Here are some specific problems that you'd encounter:
- 1Sticky bean hoppers prevent coffee beans from flowing smoothly into the grinder.
- 2Machine grinders become gummed up, causing your coffee grounds to stick together.
- 3The screens on the brew units and portafilters become clogged. With that, your espresso machine will struggle to produce brewed coffee. If it does produce a cup of coffee, it'll be flowing out really slowly.
- 4Issues with your machine. Perhaps the worst of it all, you'll need to get your machine thoroughly cleaned by a licensed service center.
With the above, however, it's important to note that these issues only occur if you use exceptionally oily coffee beans.
How Do You Brew Oily Coffee Beans At Home?
Wondering how you can go about brewing oily coffee beans at home? Here are a few different ways you can go about doing so:
Use a Coarser Grind
If you've got relatively oily coffee beans one exceptionally dark roasts, you'll want to ensure that you're grinding your coffee slightly coarser than normal. A coarser grind size will ensure that your dark roast has a lovely rich and chocolatey flavor rather than a bitter one.
With a coarser rind, your dark roast will produce a full bodied cup of bold coffee that's robust and has a good amount of flavor.
Lower The Water Temperature
Another trick that's typically used is to lower the water temperature. Heat compromises the taste of dark, oily beans. So, if you're looking to brew the perfect cup of coffee, the best way to do it is to drop the temperature as low as 195 degrees Fahrenheit.
Taking that logic into consideration, these brewing methods are excellent for producing excellent cold brew coffee with bolder flavors since the low temperatures will still extract important flavor compounds without the strong and bitter notes.
Stick With Cold Brew
If you've got oily and old coffee beans, it's best to stick with cold brew. The bean won't be particularly flavorful, but you can still resurrect the coffee bean in a cold brew.
Frequently Asked Oily Coffee Bean Questions
Are oily coffee beans good for espresso machines?
They're not particularly great for espresso machines. Not only could they affect the taste of your espresso, but the oil from the coffee bean could also compromise how your espresso machine operates.
How do oily coffee beans change during the roasting process?
The increased temperature causes water to turn into gas, creating a high pressure level within the bean. This changes the cellulose structure of the bean, and over time the bean changes from cellulose to charcoal.
Can you dry oily coffee beans?
You should never try to get rid of oil from the coffee beans as this cannot be done. Don't try and wash the oils away either, as you'll end up with a roast and brew that has no flavor.
Do dark beans or dark roasts have more oil?
Dark roasts tend to have more oil than light roasted coffee and dark beans as the beans are exposed to higher temperatures and the oil is drawn out. Dark beans on their end are full of oils, but the roasting process is what brings them to the surface.
What type of oil is in coffee beans?
They have fat-like lipids that consist of triacylglycerols, tocopherols, and sterols. These are also found in vegetable oils.
Will oily coffee beans clog the grinder?
Yes, they can clog up your grinder as more oils from these beans can cause your grounds to clump together.
If you’re wondering how to grind oily coffee beans, we recommend using a burr grinder.
As seen above, just because the beans are oily doesn't mean you can't have great coffee. Instead, it depends on the roasting time, if it's roasted properly, and whether you enjoy dark roasted coffee.
Just be careful when you're grinding them, as the last thing you'd want is to clog up your machine!