Defective Coffee Beans Illustrated Guide: What Are Defective Coffee Beans and How to Identify Different Defects?

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The key to efficient manual sorting is to first decide which type of defective beans to start with. First, the inspection order is color, luster, and shape. First remove foreign objects and black beans that are obviously different in color from the raw beans, then focus on the dead beans, fermented beans, and unripe beans that lack "luster," and finally handle defective beans with strange "shapes" such as shell beans and insect-damaged beans.

Article by: Seimeido Publishing Editorial Department

Efficient Manual Sorting Through Systematic Processes

Manually picking out defective beans from large quantities of coffee beans is a rather time-consuming and labor-intensive task. However, once you master the technique, you can work efficiently.

When selecting defects from raw beans, it's recommended to spread the beans on a non-reflective black tray. Beans like fermented or unripe ones will appear slightly yellowish, making them easier to distinguish on a dark tray. For manual sorting after roasting, to better detect differences in roast color, spread the roasted beans on a tray covered with brown cotton cloth to make the sorting work easier.

Once the coffee beans are spread out, you can begin picking out defective beans, but working without a systematic approach will only waste more time. The key to making manual sorting more efficient is to first prioritize the work and think about which type of defective beans to start with. First, the inspection order is "color > luster > shape." First remove foreign objects and black beans that are obviously different in color from the raw beans, then focus on the dead beans, fermented beans, and unripe beans that lack "luster," and finally handle defective beans with strange "shapes" such as shell beans and insect-damaged beans.

Regarding the proportion of defective beans found through manual sorting, washed processed raw beans contain about 15-30% defects, while natural processed raw beans account for 40%. Of course, it's ideal to purchase raw beans with few defects from the start; however, defects are unavoidable, so you need to estimate in advance the quantity reduction after removing defective beans to calculate the necessary purchase amount. It's truly regrettable when a single defective bean ruins the coffee you've spent time and effort brewing; to avoid disappointment, if it's difficult to judge whether a bean is normal or defective, it's safer to remove it decisively.

Common Impurities in Coffee Beans

1. Stones

Coffee beans naturally dried in the sun often contain small stones, gravel, wood chips, and other foreign objects. Occasionally, glass fragments or coins may also be found.

2. Grains

Similar to stones, coffee beans naturally dried in the sun may contain grains such as corn or other seeds. Pepper kernels have also been found occasionally.

Common Types of Defective Beans

1. Shell Beans, Cracked Beans

Beans that have developed into shell shapes due to growth problems are called "shell beans"; beans damaged during processing or transportation are called "cracked beans." Both cause uneven roasting.

2. Fermented Beans

During wet processing, these beans undergo contaminating fermentation in the fermentation tank. They can also be produced when processing is delayed after harvest or when storage is improper. They emit strange odors during roasting.

3. Insect-Damaged Beans

These beans have holes formed by larvae hatching from eggs laid by pests like the coffee berry borer on coffee trees and feeding on the coffee fruit. They cause cloudiness or strange flavors in coffee.

4. Moldy Beans

These beans have become moldy due to incomplete drying, improper handling during transportation, or improper storage. Even after roasting, they still retain moldy odors.

5. Unripe Beans

These are beans from coffee fruits that were harvested before they were fully ripe. Coffee containing unripe beans will have a strong fishy smell and emit a nauseating, foul odor.

6. Black Beans

These are beans that fell and turned black before harvest, or beans that were completely damaged by fermentation. They are the source of cloudiness and putrid odors in coffee.

7. Dead Beans

These are beans that failed to develop normally, causing coffee flavor to be weak and produce strange tastes. Their color is also poor after roasting, making them easier to distinguish after roasting.

8. Stinker Beans

These are beans that were dried while still attached to pulp or where pulp removal was incomplete. Stinker beans release iodine-like odors or earthy tastes.

9. Parchment Beans

These beans retain inner fruit skin due to incomplete hulling or other reasons. They cause astringency or miscellaneous flavors in coffee.

Using Non-Reflective Black Trays to Identify Raw Beans

Different tray colors change the visual effect of distinguishing raw bean colors with the naked eye. Compared to the white tray on the right, the black tray on the left provides clearer visibility. However, reflective black trays are not suitable.

Content source: "The Details of Perfect Coffee: From Bean Origin, Cupping Taste, Roasting and Grinding to Brewing Extraction - Precision in Every Step," Dialect Culture Publishing

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