FORMULA TO CALCULATE THE ROTATION OF THE COFFEE ROASTING DRUM

Coffee beans during the roasting process (or in other words, coffee beans roasted in a roasting drum) will be affected by two main forces: Gravity (P) and centrifugal force (Flt).

 Eplain symbol:

P: Gravity

Flt: Centrifugal force

m: is the mass of coffee beans

g: is the acceleration due to gravity (g: about 9.78-9.83 m/s², commonly used value g = 9.8m/s²)

a: is the centrifugal acceleration of the coffee beans

r: is radius of roasting drum

ω: The angular velocity of roasting drum

T: is the rotation period of the roasting drum (the time of the drum rotation 1 revolution)

Instead:

In order for coffee beans to not stick to the roasting drum during the roasting process, the centrifugal force must be less than gravity ( Flt < P )

⇔ m.r. 4.π²/T² < m.g

⇔  r. 4.π² < g.T²

⇔  r. 4.(3.14)² < 9.8.T²

⇔  r. 4,02< T²

   ̴̰    2√r  < T (T = 60/RPM , RPM: revolutions per minute)

=> 2√r <  60/RPM   => RPM < 30/√r  (r: meter unit)

π= 3.14

 g = 9.8

So, the RPM of the roasting drum needs to rotate less than 30/√r

According to experience, rotating: 85 – 90% RPM is reasonable.

For example: The roasting drum has a radius is 500mm = 0.5m => r = √0.25

RPM < 30/√0.25  = 30/0,5 = 60 (rpm), Choose the number of revolutions to roast from 51- 54 (rpm)

Through analyzing the above formula, we see that the rotation speed of the coffee roasting drum is inversely proportional to the radius of the coffee roasting drum. The larger the coffee roasting drum radius, the slower the rotation speed. Whether the coffee roasting drum rotates too fast or too slow also directly affects the quality of roasted coffee.
In case the roasting drum rotates too slowly (Flt < P) and the gravity is too great, the coffee beans will tend to fall down and not be stirred much, leading to a situation where some beans receive a lot of heat and some beans receive less heat (scorched and burned, ripening unevenly).
In case the roasting drum rotates too fast (Flt > P), it means that the centrifugal force is too large, and the coffee beans will be pressed against the wall of the roasting drum, also leading to scorched coffee beans.

Through the above analysis, customers can also easily calculate and adjust th drum rotation speed for your coffee roasting machine they are using accordingly.

If customers are unclear, they can contact the following information for better advice and support:
DUONG THANH DTC LIMITED COMPANY
https://marsroaster.com/
Hotline: 096 899 2211 – 093 770 2211
Whatsapp: (+84) 937 70 22 11
Intergram: (+84) 937 70 22 11

Showroom: No. 415F Nguyen Van Ba street, Truong Tho Ward, Thu Duc City, Ho Chi Minh City, Vietnam
Factory: No. 50 Dan Chu street, Hiep Phu Ward, Thu Duc City, Ho Chi Minh City, Viet Nam