What are the reasons for oil on the surface of coffee beans?

The appearance of oil on the surface of coffee beans is a common phenomenon, which gives coffee a unique aroma and taste. However, this phenomenon is not caused by a single reason, but by the combined effect of multiple factors.

First of all, coffee beans are rich in oil. There is a layer of tissue called "endosperm" inside the coffee beans, which is rich in fatty acids and triglycerides. When the coffee beans are roasted, the high temperature will decompose these fatty acids and release a large number of volatile compounds and aromatic substances. These compounds gradually evaporate to the bean skin along with the water and form the oil seen on the surface.

Secondly, gas pressure is also generated during the roasting process. When roasting at high temperatures, moisture is quickly converted into water vapor inside the bean, generating a large pressure. When it reaches a certain level, the pressure will push the internal liquid into the bean skin through tiny cracks or holes and form tiny particles or droplets. As time goes by and the temperature rises, these particles or droplets gradually gather and form visible oil.

In addition, the variety and processing method of coffee beans will also affect the oil production. Different varieties of coffee beans have different chemical compositions, so the oil production will also vary. At the same time, in the coffee production process, including picking, peeling, fermentation and other links, they may affect the internal structure and chemical composition of the beans, and thus affect the surface oil production.

Finally, the roasting level is also one of the important factors that cause the oil on the surface of coffee beans. The roasting level determines the degree of control of the temperature and time inside the coffee beans. Too light or too deep roasting may lead to uneven heating and incomplete release of volatile substances, thereby increasing the oil on the surface.

In summary, the oily phenomenon on the surface of coffee beans is caused by the combined effect of multiple factors during the coffee making process. These factors include fatty acid content, gas pressure, variety and processing method, and roasting level. For those who love to enjoy the rich aroma of coffee, this oily phenomenon is undoubtedly a delicious experience.