Why Are Some Coffee Beans Oily?

Close up of roasted coffee beans.

There's nothing better than a fresh batch of coffee beans – the fresher, the better. On a recent quest for the freshest roast in my hometown, I found a bag of dark coffee beans that had a shiny coating of oil. Did this mean the beans were fresh, or had they been sitting on the shelf for too long?

Why are some coffee beans covered with oil? All coffee beans contain oil; when the bean is exposed to air or heat, some of the oil will start to leak out. If your beans are oily, it means that they naturally contain more oils, were over-roasted, or have been left on the shelf for a few weeks.

Oily coffee is usually within a few weeks of roasting and probably has a strong flavor. Because every batch of coffee is different, the presence of oil can say a lot about how the beans were grown and roasted. Now that I know what to look for, I've been a lot better at choosing a roast I know I'll like.

Why Your Coffee Beans Are Coated in Oil

Freshly picked coffee beans.

Coffee beans are actually the seeds found inside of coffee cherries. When these seeds are first harvested from the fruit, they're bright green and full of both sugars and juices.

Coffee beans are dried immediately after harvesting. Most of the moisture evaporates, leaving only the sugars and the coffee bean oils. These oils contain most of the flavor and caffeine inside the seed.

A coffee bean that has more oil is usually darker and weighs more. These beans are often thought to have a “bolder” flavor, although oil content is not the only thing that affects a coffee bean's flavor profile.

Coffee oil remains trapped inside the seed until the bean is roasted. As the heat dries out the seed, the shell cracks, and the coffee oil starts to oxidize in the surrounding air.

The amount of oil that is initially oxidized depends on how long the coffee was roasted and how much oil was already in the bean. This oil turns into the shiny coating that you can see on most dark roasts. More oil will start to leak out of the beans with time, which can result in month-old beans having the same shiny coating as fresh ones.

This means that an oily coating on your coffee beans is usually caused by one of three reasons:

  • The beans were already full of oil. Dark, heavy, and oily beans will have a coating of oil when they are first roasted. This coating will start to fade as the beans age and dry out.
  • The beans were roasted for a long time. When coffee beans are exposed to heat, the oils inside are brought to the surface. Dark, fresh-roasted beans usually have a shiny coating of coffee oil and a strong smell.
  • The beans have been allowed to sit. Coffee beans slowly excrete oils over time. Even dry roasts will develop a shiny coating if you leave them on the shelf for a few weeks. After a few more weeks, this coating will start to evaporate, and the beans will be both dry and stale.

Oil on Fresh Coffee Beans

It's actually very normal for fresh, dark-roasted coffee beans to have an oily sheen. This is because dark beans are already full of oils, and the roasting process brings these oils to the surface.

Some people think that oily coffee beans have more flavor, while others always prefer a drier roast. Changing the heat used and the roasting time will change how much oil is present on the beans; these differences in the roasting process are part of a roaster's signature taste.

Every bean is different, and so is every roasting process. Some beans will never produce a lot of oil, even if you roast them for an extended period of time. Other coffee beans are full of flavorful oils and will have a shiny coat no matter how long you roast them.

Regardless of the amount of oil, you can tell whether your roast is fresh by the strength and quality of the aroma. Fresh roasts have the strongest scent and usually smell green, floral, or spicy. As the roast gets older, the scent will start to fade, and beans might even smell dusty.

Oil on Older Coffee Beans

The roasting process doesn't always coax the oil out of coffee beans. If the roast is dry, you might not see any oil when you first open the bag – but that doesn't mean it's not in there.

All coffee beans will start to oxidize once they become exposed to air. After a few weeks on the shelf or in the warehouse, your coffee beans will start to develop an oily coating that looks similar to the one on freshly-roasted beans.

Coffee beans are still drinkable at this stage. In fact, some people might enjoy the rich and slightly dark taste that comes from a slightly aged roast.

After a few more weeks, the coffee oils will start to evaporate, taking most of the flavor and aroma with them. Coffee beans that have lost their oils entirely are stale. The aroma will be gone, and any coffee brewed with them will have a dry, bland, or even bitter taste.

The truth is that if your coffee beans still have visible oil, they're at least a few weeks fresh and have plenty of flavor. The next time you see oily coffee, get ready for a bold and delicious flavor experience.

Dark Beans vs. Dark Roasts

When you're talking about the color of a coffee bean, are you referring to the roast or to the bean itself? The difference is actually greater than you think; if you understand the two terms, you'll have an easier time selecting your favorite brew.

Coffee beans that have been freshly harvested are usually either dark or light in color. Dark coffee beans have more oil than light coffee beans; they also usually weigh more.

The base color of a coffee bean changes when it's roasted. Just like any kind of food, coffee beans get darker when they are roasted for a longer period of time. Depending on the original bean, some dark roasts will also develop a shiny coating of oil.

To get the lightest possible bean, you should choose a dry, low-oil coffee and roast it for a short amount of time. To get an extremely dark bean, you should choose a bold, high-oil coffee and roast it until almost all of the moisture is gone.

You can also roast light beans for a long amount of time or prepare dark beans with a golden roast. Variations in this process will decide the final color of the beans and the way your fresh batch of coffee tastes.

Influencing the Flavor of Your Brew

The strength of a cup of coffee depends on the type of beans you use and how they're treated. Although it's true that oily beans typically have more flavor, changing the brewing method might reduce or enhance the taste.

For bold coffee, you can:

  • Choose an oily coffee bean
  • Buy a darker roast
  • Grind your coffee beans extremely fine
  • Use more coffee grounds
  • Brew your coffee for longer

To get light coffee, you should:

  • Use drier coffee beans
  • Choose a lighter roast
  • Grind your coffee more coarsley
  • Use less coffee grounds
  • Brew your coffee for a shorter amount of time

Because all of these factors can affect the strength of your roast, it's easy to customize the flavor of each batch of coffee. Try using less of a dark bean to get a sweet and mild cup. Alternatively, you can use a fine grind and an extended brewing cycle to really bring out the flavor of your favorite golden roast.

Related Article: WHICH COFFEE IS STRONGER LIGHT ROAST OR DARK ROAST?

Related Questions

How long do coffee beans last?

Coffee beans can be used for up to 6 months, but you'll get the best flavor if you brew them within 1 month after roasting.

How can I tell if my coffee has gone bad?

Stale coffee can be identified by dry beans, reduced color, and a bland aroma or flavor. Because coffee beans don't contain a lot of moisture, it's usually safe to drink stale coffee, although the taste may be unpleasant.

Can coffee bean oil stain your clothes?

Coffee oils can stick to your clothes and cause a hard-to-clean stain. To get it out, try using laundry detergent, vinegar, or contact lens solution.

Related Article: WHY ARE COFFEE BEANS ROASTED?