Why Coffee Beans Are Oily? | What Does It Mean?

Last Updated on October 21, 2021 by John Moretti

What can be more special than having your daughter taking time off from her busy schedule to join you for a quick cup of coffee!  In anticipation of the joy this event will bring, the age-old ritual and pleasurable moments in the brewing of fresh coffee are harshly interrupted at the discovery that the coffee beans are oily!  So what does this mean?

When coffee beans are roasted, the green beans turn brown, and the longer the roasting process, the higher the temperature and the darker they become.  During this long roast, much of the oils and oil compounds are released and appear on the surface, giving the beans a greasy sheen making their appearance oily. 

There is an ongoing debate amongst the coffee-drinking population on which roasts are the more flavorful, the darker oilier bean, or the medium to lightly roasted bean.  

Are oily beans good or bad; do they produce the bolder coffee, how to avoid them, and have other uses; are just a few interesting specifics of these darker roasts.

How do Coffee Beans Become Oily?

coffee roasting process

When the green coffee beans are heated during the roasting process, the natural lipids, carbohydrates, caffeine, water, and sugar have different reactions to the heat.  Once the beans turn a brown color, the roaster will remove the beans, and if a darker roast is required, will continue with the roasting process.  

At this point, oils from the lipids come to the surface of the beans forming a shiny, oily coating.  These dark-roasted coffee beans are referred to as being oily. 

Although all beans contain oil, the lighter or medium roasted beans are drier, but the longer they remain in your kitchen, these oils will react over time with the oxygen, and these beans will become oilier.

How Do You Know The Coffee Beans Are Oily?

An easy way to tell if the beans are oily is by touching or holding them.  The beans may feel sticky to the touch and will leave an oily residue on your hand.   If lighter roasts don’t dispel any residue, then look at the inside of the coffee bag for signs of oil. 

Are Oily Coffee Beans Good or Bad?

espresso dark roast

Some coffee drinkers and roasters believe that oils in coffee beans should stay locked inside the beans, resulting in the coffee tasting bitter and acidic.  Others would argue that the oily beans add a smoky flavor to the coffee.

The oily sheen could be a good sign of freshly roasted coffee, but that coffee has become stale if the dark roast lacks oil.  

Most espresso drinkers believe that the darker roast and oilier bean make a better cup of coffee.  They refer to the light and medium roasted coffee beans as being non-oily.  These debates are ongoing, but it is rather more about the quality and roast of the coffee bean that will determine a great coffee.

However, the oils produced from the darker roasts may harm the espresso machines and grinders but can be alleviated by using a burr grinder or a French press.

Does The Oil In The Darker Bean Influence The Taste Of The Coffee?

The darker the coffee bean becomes, the more oil will be seen on the surface.  Very dark roasts have a distinctive burnt and bitter taste, partly due to the flavors of the origin of the bean being lost when roasted.

In addition, the oils compact on the components of grinders become rancid over time, and this rancid oil will leave an unpleasant after-taste in the coffee.

Do Oily Beans Produce Bolder Coffee?

bold coffee

Dark roasts have a sweeter flavor due to the longer roasting process when the sugars in the beans have time to caramelize.  This roasting process enables the bean to develop a richer and fuller body leaving a lingering buttery taste on the mouth.  

A bolder taste is enhanced by modifying the number of scoops of coffee to water, and if a stronger taste is desired, brew the coffee for longer.

The Darker beans have the least acidity, and because they’re roasted, the longest have the least amount of caffeine.  Blending the dark and medium roasted coffee will produce a silken taste as the medium coffee contains more acidity, which will help to round out the flavor.

3 Ways To Avoid Oily Coffee Beans

The best ways to avoid oily coffee beans is to:

  • Buy light roasted or medium roast coffee that has no oily surface.  Should there be signs of an oily film, these beans have been left unpackaged for too long after the roasting process, and this coffee will taste bland and stale.
  • Seal your opened packet of beans in an airtight container to prevent them from being exposed to oxygen, which will cause a chemical reaction, and the beans will become oilier sooner than anticipated.
  • Avoid buying dark-roasted coffee beans. 

Other Uses For Oily Coffee Beans

Should you not want to use coffee beans that have turned oily, here are some other ways to use them:

  • Add the beans to the compost soil mix for your garden.  Grind the beans in a burr grinder, and adding them to the mix will improve the quality of the soil.
  • Mix the ground beans with water and soap to make a scrub to remove stubborn stains in your kitchen or bathroom.
  • Ants do not like ground coffee, so scatter some coffee in their area if you have an ant problem, and they will soon move away.


The longer roasting process produces a darker and oily coated coffee bean, ideal for brewing espresso coffee.  The bean develops a richer and fuller body with a lovely buttery taste.  When deciding if darker beans with an oily sheen are good or bad, consider the overall quality of the roasting process and the freshness of the bean.

Lightly to medium roasted beans are drier, and if not stored in airtight containers, are exposed to the oxygen in the air and turn into dry and stale coffee beans.

Although the darker roasts make the bolder and stronger cup of coffee, personal taste and preferences could make this statement debatable. Be the bean oily or non-oily, they are both brewed and enjoyed by all who love the taste of coffee.