Why do coffee beans become wrinkled after roasting?

Why do coffee beans become wrinkled after roasting?

Coffee is one of the most popular drinks in the world, and the roasting process of coffee beans is a key step in making delicious coffee. However, you may have noticed that the surface of coffee beans often appears wrinkled after roasting. So why do coffee beans become wrinkled during the roasting process? This article will take a deeper look at this question.

1. Gas release

When coffee beans are heated, the water inside begins to evaporate and turn into gas. This process is called dehydration. As the water gradually leaves the bean, pressure begins to build up in the internal space.

Because the outer shell forms a barrier to gas release, the internal pressure continues to increase until it exceeds the limit that the outer shell can withstand. When the pressure exceeds the strength of the outer shell, it will cause the outer shell to crack or deform and wrinkles to form on the surface.

2. Changes in internal structure

During the roasting process, the fiber structure inside the coffee beans will also change. The originally tightly arranged fibers begin to loosen and gradually expand during the heating process. This expansion causes the volume of the beans to increase, and also puts greater pressure on the shell.

When the internal fibers become loose, they can no longer provide enough support to keep the surface of the beans flat. Therefore, after roasting, the surface of the coffee beans will appear wrinkled, irregular, or even bumpy.

3. Coking reaction

In addition to water evaporation and fiber structure changes, coffee beans also undergo a caramelization reaction at high temperatures. This is a complex and diverse quality transformation process in which some organic substances are oxidized and new aroma substances are produced.

However, the gases produced during the caramelization reaction also put pressure on the coffee beans. When the gases cannot be released smoothly, it will cause wrinkles and deformation on the surface of the beans.

4. Roasting degree

Finally, the degree to which the coffee beans are roasted will also affect their appearance. Different degrees of roasting will produce different colors and textures. Generally speaking, the surface of lightly roasted coffee beans is relatively flat, while dark roasted ones are more likely to have wrinkles.

This is because during the deep roasting process, the internal temperature of the coffee beans is higher, and they experience more water evaporation, fiber structure changes, and gas release. These factors work together to make the surface of the deep roasted coffee beans more wrinkled.

Summarize

In summary, during the heating and dehydration reaction of coffee beans, changes in internal structure and gas release, the shell is affected by pressure and cracks or deformation occurs, and wrinkles are formed on the surface. In addition, the complex reactions carried out at high temperatures will also cause pressure on the coffee beans.

It is also important to note that different degrees of roasting also affect the appearance of the coffee beans. Therefore, the wrinkled appearance of the coffee beans after roasting is the result of a combination of factors.