Why is there oil on the surface of roasted coffee beans? "interpreting the Secrets of Coffee with Science"

For professional baristas, please follow the coffee workshop (Wechat official account cafe_style)

Coffee beans look shiny on the surface, which comes from the lipids contained in the beans themselves. Arabica coffee beans contain nearly twice as many lipids as Congolese coffee beans, so Arabica seeds are more likely to produce oil if they are roasted at the same degree. The special emphasis on "the same baking degree" is that the way of oil production is also affected by the way of baking.

The oil contained in coffee beans is squeezed to the surface by carbon dioxide produced during baking. The deeper the baking, the more carbon dioxide. As a result, all the oil from the deep-roasted coffee beans has seeped out during the baking process. The oil that seeps out after baking for a while is pushed out when the remaining carbon dioxide in the baked beans is discharged. Coffee beans continue to emit carbon dioxide for a month after baking, especially in the first few days of baking, so on most occasions it is possible to judge why coffee beans produce oil in those days.

Some people like and some people don't like the oil oozing from coffee beans.

So, is it possible that some of the raw beans baked with the same baking degree produce oil and some do not?

This can be done through some manual control methods. For example, when roasted with strong firepower, coffee beans quickly produce carbon dioxide, causing intense bursts.

Coffee beans made by this roasting method usually produce oil easily. On the contrary, coffee beans baked at low temperature and slowly produce carbon dioxide and burst more slowly, so roasted coffee beans are not easy to produce oil. So we can also speculate the way of roasting from the oil production of coffee beans.