Adding protrusions to the inner wall of the roasting container has another significant advantage besides increasing the total area.　

When roasting, you may sometimes see the beans burned black. This is due to the inner wall of the parching pan which is sufficiently flat from the viewpoint of the size of the beans. In other words, the beans and the wall are in surface contact. If the contact area is large, a large amount of heat-dense conductive heat is transferred from the hot container to the beans, resulting in that unpleasant. To prevent any charring, making the contact area with beans as small as possible is necessary.

Next, arrange a regular quadrangular pyramid of the same size without any gaps on the specific area, and reduce the size gradually. You will find that the total area of the inner surface of the container is always the same even after change of the size because the number of the quadrangular pyramid changes.

Try to reduce the size of the regular quadrangular pyramids lined up uniformly to 2 mm or less. In other words, try to reduce the distance between the vertices of adjacent quadrangular pyramids to 2 mm (base is 2 mm) or less。

2 mm is the value drawn from the size of the beans。

Among the length, width, and thickness of beans, the smallest value is the thickness. In the figure above, it is T. I measured the thickness of several kinds of beans in my house and found that the smallest beans had a T of about 3 mm. From this fact, I concluded that even the most petite beans in the world would be larger than 2 mm.

When the distance between the apex is about 2 mm, the beans are much larger, so the beans cannot enter the gap between the protrusions. The beans are held by the tip of the quadrangular pyramid so that the contact between bean and container is point contact rather than surface contact, making the contacting area extremely small.

As a result, the conductive heat transfer from the container also decreases. This also results in significantly suppresses bean charring.

As mentioned above, adding protrusions to the inside of the parching pan increases the amount of radiated far-infrared rays, making roasting more efficient and preventing the beans from burning.