Why is coffee bean watches always oily? Are the oil out of the coffee beans stale? Are oily coffee beans of higher quality? What is the difference between deep and light coffee?

If you are a friend who often buys beans and makes them at home, it should not be difficult to find that some coffee beans will start to grow oily after being left for a while. No matter how long other coffee beans are left, the surface still looks dry. So a very interesting phenomenon emerged: some friends thought that the oil production of coffee beans was proof of high quality, while some friends thought the opposite, thinking that the oil production of coffee beans was due to moisture and a sign of declining quality.

In fact, these two ideas are basically wrong. Oil production of coffee beans is a normal phenomenon. It is neither a proof of high-quality coffee nor a sign of moisture (when stored properly)! Why? Because coffee beans themselves contain certain water-soluble lipids, these oils will overflow the bean surface under certain circumstances, forming a phenomenon that "coffee beans produce oil." When not roasted, these lipids wrap around the fiber matrix of the coffee beans due to the tight structural organization of the raw beans, and are firmly "locked" in the coffee beans. It was not until after the raw beans were baked that the lipids leaked out of the bean surface. As we all know, during the roasting process, the continuous heat provided by the roaster will cause the coffee beans to continue to expand, because the pores in the cell walls in the coffee beans will be expanded and a large amount of carbon dioxide will be stored.

After the roasting is over, the coffee beans return to normal temperature and pressure, and the carbon dioxide stored in the beans will begin to be discharged. At this time, the lipids in the coffee beans can spill out of the beans with carbon dioxide, producing the phenomenon of oil. But as Qian Jie said, the phenomenon of oily production only occurs on some coffee beans, and these oily coffee beans usually have a relatively intuitive characteristic, that is,"the roasting degree is relatively deep."

Qianjie mentioned earlier that coffee beans will continue to expand due to heat energy, and then the structure will become loose while expanding. Therefore, when the coffee beans are roasted more deeply, the more heat they receive and the greater the expansion. The larger the amplitude, the looser the structure will be. The loose structure will contain more carbon dioxide and make the adhesion of lipids more loose, so naturally, the oil will more easily overflow the bean surface. Below are the two beans from the Front Street Bean List. They are Front Street Papua New Guinea·Bird of Paradise, which is mid-deep baked and mid-deep baked, and Front Street Sumatra·Golden Mantelin, which is mid-deep baked and mid-deep baked. Their baking dates are the same, and they are all baked five days ago. You can compare the degree of oil extraction between them.

In addition, the speed of oil extraction is also affected by the degree of baking. For the same bean, the deeper it is baked, the faster it will produce oil. The two beans in the picture above began to show obvious oily shine a few days after roasting. If the roasting was deeper, the coffee beans would show obvious oily shine on the day the roasting was completed. Then Qianjie mentioned earlier that the degree of baking is only one of the influencing factors. In addition to the degree of roasting, the oil yield of coffee beans is also affected by the processing method, roasting method, and bean density. For example, some severely anaerobic coffee beans will yield oil more easily than conventionally processed coffee beans with the same roasted coffee beans, because the structure of the beans has already changed greatly during processing, such as making the density lower, so the same curve will allow them to be roasted deeper and more likely to yield oil.

The explanation of the roasting method of coffee is more complicated. We can simply understand that the difference in firepower and time used during roasting changes the expansion rate of coffee beans, so the degree of oil extraction of coffee beans will also be different. But because many friends hardly come into contact with baking in daily life, Qian Jie will not elaborate too much here. To sum up, we can know that whether coffee beans produce oil or not has much to do with their quality. Oil extraction will not have a direct impact on the quality of coffee, but it needs to pay more attention to storage methods, because when beans are extracted from oil, they will be more likely to undergo qualitative changes. If they are not stored in a suitable environment, then coffee beans will easily have a negative taste. So regarding this point, everyone can still pay attention to it at ordinary times ~

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