If you have ever come across oily coffee beans, you've probably been puzzled why some have a glossy surface while others look dry. What is the backstory? Does the oil mean there is more flavor or is something wrong with the beans?
Typically, coffee beans that seem oily are deeply roasted and have a dark brown hue. When coffee beans are roasted to a dark roast, they not only become a very dark brown, but the roasting process causes many of the oils and fatty chemicals inside the bean to rise to the surface, giving them a greasy sheen.
A layer of grease on coffee beans does not necessarily signal that they are of low quality or too old, but it does point to a few things to look at. We'll go through why your coffee beans could be oily and what that may tell you about your coffee below.
Where Does the Oil on Coffee Beans Come From?
To understand why some coffee beans are oily, we first need to talk about what’s going on inside those little beans.
Hundreds of compounds are responsible for the taste we get from coffee. Coffee beans aren’t actually beans at all and are instead the seeds found inside coffee cherries. When these seeds are originally taken from the fruit, they are brilliant green and full of sugars and liquids. Carbohydrates, amino acids, water, caffeine, and lipids are all found within the bean.
Fatty lipids, such as triacylglycerols, tocopherols, and sterols, account for 15 percent of the coffee bean’s makeup. These oils contain significant flavor components and influence the texture and taste of brewed coffee. The majority of this coffee oil is kept within the seed, where it will be used as nutrients for a young plant following germination. Green coffee does not appear or feel greasy to the sight or touch. It is only after roasting that those lipids begin to emerge.
During roasting, heat destroys the endosperm and makes the outer shell more porous, enabling coffee oils to rise to the surface. The darker the roast of the coffee, the more porous the outer shell, and, as a result, the more oil will seep through to the surface of the coffee immediately after it has been heated.
Why Your Coffee Beans May Be Oily
If you enjoy dark roast coffee, you will notice an oily sheen more often than if you drank a lighter roast.
All coffee beans, whether light, medium, or dark roast, will have a shine on them shortly after roasting. Because the dark roasts have been roasted to the greatest temperature and for the longest time, they have a lot more of this shine than the other roasts. They produce an oily appearance that can be concerning for those who are not used to it.
Understanding the Roasting Process
It's useful to understand the roasting process in order to comprehend the oil on your coffee. The first and second cracks are the most important stages to understand. Both of these stages are named for the sound made by the coffee as well as the actual happenings inside the beans.
The first crack occurs in part because the heat in the roaster causes the moisture within the seeds to pressurize and turn into steam. The Maillard process, a heat-induced interaction of amino acids and carbohydrates, also causes the beans to brown. The cellulose structure of the beans finally breaks down, resulting in an audible shattering sound that coffee roasters refer to as "first crack."
If the beans are subjected to heat after the initial crack, the pressure of the gases released inside the seed increases, and finally they burst out of the more-degraded cellulose, producing a secondary, quieter pop sound known as the second crack. Second crack is also the moment at which the cellulose becomes porous enough to enable some oil to pass through, however, all coffee will ultimately release oil after being roasted if left alone for a long enough period of time.
Are Oily Coffee Beans a Bad Thing?
Is it good or bad to find oil on a coffee bean? It's not that simple. Every bean is unique, as is every roasting procedure. Even if you roast them for a lengthy amount of time, certain beans will never create a lot of oil. Other coffee beans are rich in delicious oils and will have a glossy coat regardless of how long they are roasted. So how do you know if your coffee is good or bad?
Does Oil Equal Freshness?
Oil on beans doesn't always equate to freshness. It's usual for new, dark-roasted coffee beans to have an oily sheen. This is due to the fact that dark beans are naturally high in oils, and roasting brings these oils to the surface.However, light and medium roast coffee beans slowly excrete oils over time. Even dry roasts will develop a glossy sheen if left on the shelf for a few weeks. After a while, the coating will begin to evaporate, and the beans will become both dry and stale.
Because there is no precise calculation for how much oil will surface after a specific number of weeks or even months, it's always better to look for a roasted-on date on the beans. However, while the glossy surface of oily coffee beans isn't a clear sign of quality or age, it is something to avoid if you like a lighter roast or if the beans aren't particularly dark and no roast date is provided.
Do Oily Beans Taste Better?
Does the presence of flavor in coffee oils imply that oily beans provide tastier coffee? No, not exactly. Oils are exposed to air once they reach the surface. When this happens, they lose complexity and begin to take on less agreeable flavors as they deteriorate. If there is oil on the surface of a medium- or light-roasted coffee, it has most likely been there for a long time and will taste flat and stale. An extremely dark French or Italian roast, on the other hand, may seem greasy immediately.
Are Oily Coffee Beans Bad?
Oily coffee beans are not inherently undesirable; they are merely a characteristic of a well-roasted dark roast. While roast degree is a personal taste, drinking fresh coffee will always result in a nicer cup. If you enjoy the flavor of an exceptionally black roast, go for oily beans in general. But remember that more oil gets to the surface of the bean not only during longer roasting durations but longer storage times after roasting as well.