Why do coffee beans produce oil?

Why do coffee beans produce oil? This is a common question, and the answer involves the chemical composition of coffee beans and the roasting process. When coffee beans are roasted, the oil inside is released, forming the oily sheen seen on the surface.

First of all, we need to understand that coffee beans are rich in oil. Before being roasted, coffee beans contain a large amount of fatty acids and triglycerides. These substances will decompose during the heating process and release to form oil.

Secondly, during the roasting process, the temperature gradually increases, causing the moisture inside the coffee beans to evaporate and generate pressure. When a certain temperature is reached, the pressure will be enough to break through the outer protective shell (called the "silver skin"), allowing the moisture and gas inside to escape.

At the same time, dry distillation at high temperature is also one of the reasons why coffee beans appear shiny on the surface. Dry distillation refers to the process of decomposition of organic matter in the absence of oxygen. During the roasting process, substances such as fatty acids and triglycerides inside coffee beans will undergo dry distillation reactions, producing various volatile compounds and oils.

Finally, the glossiness on the surface of coffee beans is also related to the degree of roasting. Different degrees of roasting will lead to different chemical changes and the amount of oil released. Generally speaking, light roasting (such as latte) will make the coffee beans retain more moisture and less oil; while deep roasting (such as French roasting) will reduce the moisture inside the coffee beans and release more oil.

In short, the reason why coffee beans appear shiny on the surface is because they contain a lot of oil inside, which is released during the heating process. At the same time, the increase in temperature, pressure and dry distillation reaction are also one of the reasons for this phenomenon. For those who like to taste different flavors of coffee, understanding the chemical processes behind them can better understand the roasting and taste of coffee.