If you have seen dark roasted coffee beans that look shiny or as if they are covered in some kind of oil and wondered what it is, then you are in the right place. Every coffee bean is different and some may be more greasy than others, but it is a natural process that happens to all coffee beans. This “shine” on coffee beans is a type of oil that is naturally contained in the bean.
Coffee beans become greasy because lipids from inside the bean come to the surface like oil when roasted. This usually happens with dark roasted beans, and more of these lipids can seep out of the beans the longer they are roasted.
In this article I will explain where the oil on coffee beans is and what it means about your coffee beans. There may be a few things to watch out for when looking at oil on your coffee beans.
What do greasy coffee beans mean for your brew?
Have you seen crema on a good shot with espresso before? It is a great example of what coffee oil is and what it does for your coffee.
Crema is an example of what happens when the coffee oils are inside your coffee beans, but what if they are released before you brew your coffee?
Coffee is a nuanced and refined beverage, so there is usually no sweeping answer to what greasy coffee beans mean. You may even hear conflicting answers like “greasy coffee beans are not fresh” or “greasy beans are a sign of old and stale beans”. However, this is because everyone’s palates are different, and some may prefer some tastes over others.
As a rule of thumb, you should typically stay away if you see medium-sized or light roasted coffee beans with a thick layer of oil on them.
These oils need to be released from the bean from a longer toasting time, and a light or medium roast is not long enough to release these oils.
We can then deduce that these light or medium roasted beans with a layer of oil may be older beans or may have been stored in a wrong container, resulting in the oil.
Read about how to properly store your beans here. If you see this oil on dark roasted beans, it is natural and does not mean that these beans are oily or have been stored incorrectly.
Oily coffee beans are the result of a chemical reaction that occurs when the coffee bean meets oxygen. This usually happens more with darker roasts, as the inner shell that protects the coffee bean is damaged by the heat.
Darker roasts lose their flavor faster and usually have more oil on them because the shell gets damaged. However, each bean will eventually develop this oily sheen on top of the bean if left exposed to enough oxygen.
Properly roasted beans, even dark roasted, should not have a greasy layer on the surface until a few weeks. Rest assured, your coffee is safe as long as you buy fresh coffee every few weeks.
Greasy beans can also become sticky and clog your coffee or espresso machine. Over time, this oil can build up to become a gummy sticky mess that is very difficult to clean up. It may also cause it to clump together and stick together to prevent proper extraction.
Here’s how to tell if your coffee beans are fat
The easiest way to tell if your coffee beans are fat is to use your hands. Touch your prayers and feel if there are any residue left on your hand. Some beans may even feel a little sticky!
Lighter roasts usually have no leftovers, but you can also check the inside of your coffee bag. Sometimes the inside of your bag can also be greasy due to the coffee beans.
Roasting levels are usually based on your personal preferences, but freshness is something that any coffee drinker should enjoy.
Here are the guidelines you need to follow when buying new beans:
- For light roasts, if there is oil on top of the bean, they have been sitting for too long and you should stay away.
- For medium roasts, the same rule applies. Medium roasted coffee should not normally have any oils on it.
- For dark roasts like French or Italian roasts, you can expect them to be a little greasy, so drink these beans for the roasted flavors instead of the bean’s flavor profile. For these beans, try to choose beans that are not sticky.
Chemistry within the coffee bean
There are hundreds of chemicals that go into making a cup of coffee that we all enjoy. All of these chemicals are stored in the coffee bean, which is actually a seed of a coffee cherry.
Like many seeds, coffee beans protect carbohydrates, amino acids, water, caffeine and lipids. This goodness wrapped inside the coffee bean is usually used to help a new coffee plant grow if the seed is planted. But when the bean is roasted and run over hot water, these chemicals come together to create the drink we know as coffee.
Separately, these chemicals can taste awful. Caffeine, for example, is a water-soluble chemical that alone tastes awful. Caffeine actually tastes just bitter alone and not in the good coffee way.
Pure caffeine is actually tasteless and too bitter to swallow.
When heated, these chemicals are activated during the frying process and cause magic to happen.
Why beans become greasy during frying
Coffee beans change dramatically during the roasting process. Many people do not know that coffee beans start as a green, pale almost colorless seed because they are so used to seeing the roasted version.
The beans change color due to the heat of roasting, but this is not just a normal browning. The amino acids and sugars that are normally inside the bean undergo the Maillard reaction and are chemically transformed to produce the flavors we know and love.
Any moisture inside the bean is also converted to steam and tries to escape the bean. This is usually built up in pressure inside the prayer until a “crack” is heard. This is the inner shell of prayer that breaks apart.
This exposes the inside of the bean called the endosperm. This layer inside the bean is semi-porous, and as a result, the coffee oils inside the bean can escape to the surface.
This is why dark roasted beans tend to get fat faster than lightly roasted beans. Dark roasted beans are roasted to the second crack. This means that the inner shell of the coffee bean is even more exposed now and damaged by the heat.
The more damaged the inner shell is, the more oil escapes to the surface.
Some people may think that the shiny appearance of a dark roasted coffee bean is a good indication of good coffee. Do not let your eyes deceive you. Sometimes the best coffee is not for a shiny oily bean that catches the eye, but an eye-catching matte bean.
The fat on beans is not a good judge of what the best coffee beans are, but they give you a good idea of the quality of lightly roasted beans and are usually a good indicator of freshness.
Remember these tips the next time you shop for your coffee beans!