Understanding Milling in Coffee: From Harvest to Roasting

Milling is a crucial step in the coffee production process that involves removing the layers surrounding the coffee bean to reveal its inner essence. It is a meticulous process that requires expertise and precision to ensure the highest quality in the final cup of coffee. In this article, we explore the various aspects of milling and its significance in the world of coffee.

1. Harvesting the Cherries

The journey of coffee milling begins with the harvesting of coffee cherries. These cherries are selectively picked when they reach their peak ripeness, ensuring optimal flavor development. After harvesting, the cherries undergo a series of steps to transform them into the beans we are familiar with:

  1. Sorting: The cherries are sorted to remove any defective or underripe ones, ensuring only the best cherries move forward in the process.
  2. Washing: The cherries are thoroughly washed to remove any dirt or debris.
  3. Depulping: The outer skin, called the exocarp, is removed, revealing the coffee bean surrounded by a sticky layer called the mucilage.

2. Fermentation and Washing

Once the coffee beans are depulped, they undergo a fermentation process to remove the remaining mucilage. This process plays a crucial role in developing the flavor profile of the coffee beans. After fermentation, the beans are washed thoroughly to ensure the removal of all traces of the mucilage.

3. Drying

Drying is a vital step in coffee milling as it removes excess moisture from the beans, making them more stable during storage and preventing the growth of mold or fungi. There are two primary methods of drying coffee beans:

  • Sun-drying: The coffee beans are spread out on large patios or raised beds to dry naturally under the sun.
  • Machine drying: In regions with unpredictable weather or limited sunlight, mechanical dryers are used to speed up the drying process.

4. Hulling

Once the coffee beans are sufficiently dried, they undergo hulling to remove the parchment layer that surrounds each bean. Hulling can be achieved through the following methods:

  1. Dry method: In this method, the beans are mechanically cracked, and the parchment layer is removed using an airflow system.
  2. Wet method: The wet method involves soaking the dried beans in water to loosen the parchment layer, which can then be removed using friction.

5. Sorting and Grading

After hulling, the coffee beans are sorted and graded based on their size, shape, and quality. This classification plays a crucial role in determining the final use of the coffee beans, whether it be for specialty coffee or commodity-grade coffee.

Grade Classification
GradeDescription
AALarge, evenly shaped beans with minimal defects
ABBeans that do not meet the AA grade but are still of good quality
Screen 18Beans that pass through an 18/64-inch screen, indicating larger size
Screen 16Beans that pass through a 16/64-inch screen, indicating smaller size

In conclusion, milling is a complex process that involves several meticulous steps to transform coffee cherries into the flavorful beans we brew into our cups. Each stage holds significance in shaping the final taste and quality of the coffee. Understanding this journey from harvest to roasting helps us appreciate the artistry and dedication behind every sip.