Why Are Some Coffee Beans Oily?

Coffee beans that are oily are another part of the coffee community that causes a lot of dispute among drinkers and roasters. There are some differing opinions about oily coffee beans, what causes them and what it means for your hot beverages.

As you’ve probably clicked through to this post because you are looking for an answer to the question posed in the title or because you’ve been browsing the site and thought this post looked interesting, let’s not disappoint you on either count.

What Causes Coffee Beans to Be Oily?

Oils occur naturally in coffee beans. When they are in their coffee cherry state, the oils have a consistency closer to solids. It is once you roast coffee cherries that they fully turn into coffee beans and a lot of major changes happen.

CO2 that has formed on the inside of the bean often starts to seep out if beans have been roasted for too long. When the CO2 starts to escape the bean, it reacts with the atmosphere, more specifically the oxygen which produces the intriguing shiny and oily finish on the outside of the beans.

There are two different opinions worth noting:

  • One suggests that coffee beans that are particularly oily are bad or poorly roasted
  • The other thought is that darker roasted beans are far oilier due to the longer heating times.

The second opinion is more plausible as it falls inline with coffee roasting science. As greater amounts of heat will cause the oils and gases on the inside of coffee beans to escape and react with the oxygen in the air, it makes sense that darker roasts are likely to be oilier.

Are Coffee Beans That Are Oily, Stale?

This is something else that there seems to be a degree of misunderstanding about. It is not necessarily the case that oily beans are stale. However, lighter roasts that are not oily tend to keep their freshness for longer than their darker counterparts.

Whereas darker roast coffee beans will tend to have a lifespan of approximately seven days, light roast and medium roast coffee beans will often last anything from 10 to 14 days.

Is Bold and Strong Coffee Only Produced by Oily Coffee Beans?

Well, that really depends on what you mean by strong. If you mean they have a strong coffee flavour that is also bitter and acidic, then the answer is yes. The truth is that only happens because the beans are darker roasts and therefore more of the flavours and oils have come out or have been burnt off.

What if you have a dark roast coffee bean that is not oily in the least bit at all? Well, unfortunately, this means it is most definitely stale as there is no presence of oil whatsoever. Making a cup of coffee or two with beans in that condition would only produce a very tasteless and fairly bitter cup of coffee (if you really want to use that word to describe it)

On the subject of bold coffees. There is another misunderstanding that oily and dark coffee bean are the only kind that can produce bolder coffee. Although there is some truth in it, there is more than one way to make a very bold cup of coffee.

Medium and even light roast beans make great coffees with big, bold flavours. After all, roasting is just one part of the coffee making process that you can control. You are also able to control the brewing time, amount of beans used and the grind size of the beans.

For instance, for bolder flavours you could try the following:

  • Grind your coffee beans into a much finer grind to give them a greater surface area that will allow more water to interact with more coffee, meaning that more flavours are extracted.
  • Using twice as much coffee in the same volume of water will make your normal cup taste a lot stronger
  • An intense and stronger flavour is also possible by brewing the coffee around 1.5 times longer than the time recommended.

Important Notes About Espresso Machines and Oily Coffee Beans

We couldn’t possibly cover the subject of oily coffee beans without drawing your attention to the fact that oily beans should not be used with the super-automatic-style espresso machines. The brewing mechanism and grinder in those kinds of machines can get damaged by the oily residue on the beans. Even if it doesn’t have a noticeably dramatic effect immediately, it will eventually.

Those oils can clog up the gears and burrs and really jam up all the pipework inside the espresso machines. Therefore, we would highly recommend that you avoid using oily coffee beans in one of those machines.

If you are determined to drink an espresso that have been created using darker roasted beans, you should grind them down separately. That way you are able to clean the grinder once you finish.


There you go, folks, you now know how oily coffee beans are caused, and how you can still make use of them. Not, though, if you intend on making a nice dark roast espresso with oily beans in one of those special machines.

Whatever you do, keep in mind the tips, recommendations and advice outlined in the above post to ensure you always brew the best and tastiest cups of coffee, even when using oil-covered beans.