Glistening, oily coffee beans are eye-catching, but did you ever wonder why they have that shiny coat? Is there any difference in the taste and flavor if you choose to brew with these beans?
The oiliness from these beans has both positive and negative effects on the overall quality of your coffee. If you are curious about coffee oil, why it appears, and the puzzles surrounding it, keep scrolling down!
Below are the explanations about the phenomenon of coffee oil secretion. We also explain the importance of coffee oil to the quality of the coffee you enjoy.
What Are Oily Coffee Beans?
Coffee beans always contain oil or lipids. During roasting, high internal pressure causes these compounds to move from the cell center toward the surface of the coffee bean.
Lipids help keep volatile compounds inside cells. Volatile compounds have a high vapor pressure at room temperature, and some of them are essential to creating the flavor and aroma of coffee. This means they can be dispersed without oil.
The longer the roasting process, the stronger coffee’s taste is because the oil layer is exposed more to help retain the flavor and aroma of the coffee.
However, it doesn’t mean the longer the roasting, the better. The roaster needs to know the right timing for the great beans to achieve their best quality.
Therefore, to control the amount of oil relatively, people often have to research and classify coffee beans into many different types. Each one has a specific roasting method and process.
Nowadays, there are many types of coffee beans on the market with many different flavors such as Robusta, Arabica, Culi, Moka, etc.
Hence, to evaluate the best coffee quality, the amount of oil is one of the important criteria that coffee lovers often pay attention to in the selection process.
Refer to the section below to understand the advantages and disadvantages of high or low oil coffee beans and how they appear.
How Do Oily Coffee Beans Occur?
Why are some coffee beans oily? This is a question that many coffee enthusiasts wonder about, and the information below will explain it.
The purpose of roasting is to maximize the flavor of the coffee’s soluble chemicals. The dissolved solids give the coffee its taste, while the volatiles gives the much-needed oils that create the aroma of the coffee.
Thus, the oil appears only during and after the roasting process of coffee beans.
The microstructure of green beans is relatively dense and organized, with oils encapsulating the cellulose matrix. When coffee is roasted, the formation of steam and CO2 increases the pressure inside the bean, causing the texture of the bean to expand.
A few minutes before the first crack, the bean will swell to the point that the silver-colored skin (the chaff) will appear. That skin rolls into the core of the seed.
When the bean’s cellulose cannot expand anymore, gas and water vapor violently escape from the fissures inside and on the bean surface. As a result, you can hear a popping noise.
Roasters who want to create a light or medium roast will often stop roasting somewhere between the end of the first crack and the beginning of the second crack. After the first crack, gas generation continues, regenerating pressure inside the grain.
Meanwhile, the texture of the bean will become more brittle, preparing for the second crack stage. The main cause of the first crack is the steam pressure, and the second one is the accumulation of CO2.
As soon as the second crack happens, the oil will flow to the bean’s surface, and this is a signal of a dark roast.
That is the entire basic roasting process for coffee beans and the appearance of coffee oil.
Are Oily Coffee Beans Good Or Bad?
As a newbie, you might have heard contradicting statements from others like “Oily beans are old beans, and they have stale smells”, or “Oily beans are well roasted with the best level of freshness”.
However, having oil on coffee beans does not mean that the quality of the whole bean is low.
The oiliness has a certain effect on preserving the flavor and taste of coffee, so if you completely remove the oil factor in coffee, it means that you will never get the best taste and aroma out of your coffee.
What Are The Pros And Cons Of Coffee Beans’ Oil?
Oil in coffee beans brings good and bad points, depending on the situation. Below are the general pros and cons that most people will agree with:
Frequently Asked Questions Of Oily Coffee Beans
Here are some questions that you might have about oily coffee beans:
1. What Are The Problems Dark, Oily Coffee Beans Cause For Espresso Machines And Grinders?
People often use dark roasted coffee beans for making espresso rather than light and medium ones. The reason is that these beans deliver a stronger aroma and taste, making them ideal for such a bold drink.
Dark roasted coffee beans produce more oil than their light/medium counterparts because it takes a longer time to roast. On the other hand, there is a problem with using black-roasted oil in espresso machines and grinders.
Oily beans can damage espresso machines, especially those with super-automatic modes. This oil often clogs the machine and causes blockage or clings to the burrs of the grinder. As a result, it will cause the grinder to stop working, and you have to costly repair the machine.
Here is a quick fix you can apply at home to protect your coffee maker and grinder from being damaged by the grease produced by thoroughly roasted coffee beans.
Clean The Machine
If you love dark roasted coffee beans, you need to regularly clean the hopper or grinder. Also, be prepared for the replacement cost of your grinder every six months.
To clean the grinder, you can separate the plastic parts, then wash them in hot water with detergent. Because some parts of the grinder are electrically attached, such as the burrs, it is advisable to wipe it clean with a dry cloth.
During the cleaning process, you may need the help of a paintbrush to clean some hard-to-reach corners or deal with stubborn stains.
Stick To The Cleaning Schedules
It is necessary to clean your machine frequently to guarantee the lifespan of your coffee machine and grinder.
All coffee shops clean their grinders every night. That helps to prolong the machine’s life and reduce the risk of many problems and potential damages.
However, nightly cleanup will take a lot of time. We recommend only doing it once a week for any grinder used at home. Scheduled cleaning will keep your machines at their best performance.
2. Is It Possible To Remove Coffee Beans’ Oil From The Coffee Maker?
Yes, it is. You can use the French Press to brew a cup of coffee with oily beans because it will be easier to wash than other appliances.
Besides, if you’re concerned about oil in your coffee, don’t try removing them by water, as you’ll risk losing the flavor and aroma of your coffee. You should use a super/semi-automatic machine instead.
3. How Do We Know The Coffee Beans’ Storage Time By Checking The Oil?
One of the ways to detect coffee that has been left out for a long time is to check the coffee oil. Typically, the coffee will be packaged immediately after the roasting process to ensure freshness.
Therefore, if the coffee is freshly roasted and is packaged within the same day, the coffee beans will have less oil.
If left outside for a long time, the coffee beans will be exposed to oxygen and create chemical reactions. Thus, coffee beans will produce more oil, whether it is light, medium, or dark.
You can also base on the oil characteristics of each roast to determine how long the storage duration is. For example, for light-roasted coffee beans, the amount of oil is little, and you can feel the dryness of the beans by touching them. If you find they are oily, causing a slippery feeling on fingers, it is definitely old coffee beans left on the shelves for a long time.
By knowing more about oily coffee beans, you can understand how to roast coffee beans, store and use them more properly. Accordingly, you can distinguish between good-quality roasted coffee beans and poor ones.
If you are a person who roasts your coffee to drink, the above knowledge is vital. You need to understand the importance of the coffee roasting process and the oil secretion of coffee beans.
Hopefully, you will get the best quality beans with the oil level that you want.
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Almost 20 years already spent committed to coffee and more than 3 years of experience as a barista at Starbucks. Madelyn Doyle graduated with a Bachelor’s Degree in Nutritional Science from the University of California and finished the Coffee Skills Program at the Specialty Coffee Association (SCA).