Dry milling of coffee beans is the process by which the husks are removed from the beans so the beans may be sorted and classified.
The coffee beans will be sorted and classified by size and weight.
Dry milling of coffee beans is the process by which the husks are removed from the beans so the beans may be sorted and classified by size, weight and color.
When designing a dry mill a number of factors are taken into account. The coffee beans will be sorted and classified by size and weight. Some customers specify the size of the beans and the amount of defects they will allow.
Some customers specify the size of the beans and the amount of defects they will allow. 80% can be classified through the following means:
Using an air elevator all heavy foreign objects such as stones or any metal are removed as the coffee parchments float up the required height into the thresher.
The coffee parchments are placed into the thresher to separate the husks from the coffee beans. The husks reset aside for later use, and the coffee beans continue on through the milling process.
There are two methods to separate the husks from the beans.
One method uses friction and the other method is blades. The friction method is called ”Peladora” where the parchments are placed between rollers and the husks are stripped from the coffee bean.
The second method uses blades to cut the husks from the beans.
The coffee beans are then categorized by size and weight by sorting them through a series of sieves of decreasing size.
The sorting method continues by using vibration and air flotation to separate the beans by three qualities, heavy (1st quality), medium (2nd quality), light (3rd quality).
The coffee beans are stored in hoppers or silos until later when a stricter classification by color is done. Off-color coffee beans are removed by using an electronic sorter. The remaining coffee beans then continue on a conveyor belt where skilled workers remove any remaining defects.
The next step is ROASTING.