The proportion of defective beans directly affects coffee quality and grade classification. In Brazil, for example, a "deduction system" is used locally, grading coffee based on the number of defective beans per 300 grams of primary beans. Additionally, coffee typically requires hand sorting during processing, and only by thoroughly understanding the types and characteristics of defective beans can they be effectively removed. So, exactly how many types of defective beans are there? This article will use illustrated explanations to introduce ten common defective beans one by one, including shell beans, stones, moldy beans, fermented beans, dead beans, immature beans, shell beans, insect-damaged beans, black beans, and cocoa beans, explaining their causes, appearance characteristics, and negative impacts on coffee flavor, laying the foundation for subsequent learning about defective bean selection.

One of the key factors affecting coffee quality is defective beans, and the proportion of defective beans is directly related to the grade evaluation of coffee.

In Brazil, for example, the local coffee evaluation system used is the "deduction method," which grades coffee based on the number of defective beans per 300 grams of primary beans.

Additionally, coffee usually undergoes a hand-sorting process, and a successful hand sorting also requires a full understanding of the various types of defective beans. This shows how important defective beans are to coffee. But "defective beans" is just a general term—how many types does it actually include? Next, we will introduce: the top ten types of defective coffee beans. See how many you can recognize?

1. Shell Beans

The coffee endocarp adheres to the inner side of the pulp and often remains on washed coffee beans. These beans do not conduct heat well during roasting and may even catch fire, and they are also one of the sources of astringency in coffee.

In addition, there are also broken beans, red-skinned beans (beans formed when rain occurs during natural drying, with a flat and monotonous flavor), and underdeveloped beans (small beans that stop growing due to insufficient nutrients, with a strong taste), and sometimes impurities such as corn kernels or peppercorns are mixed in.

2. Stones

Because the harvested beans are processed using the natural drying method, they are prone to being mixed with foreign matter such as stones or wood chips.

3. Moldy Beans

Insufficient drying, or exposure to moisture during transportation or storage, can cause beans to grow blue or white mold, and sometimes they clump together. If these moldy beans are not removed, a musty odor will be produced in the coffee.

4. Fermented Beans

They are mainly divided into two categories: one is formed during washed processing when the coffee is soaked too long in the fermentation tank and contaminated by the washing water; the other is when beans are piled in a warehouse and, after bacteria attach, the surface becomes mottled. Fermented beans are not easy to identify by appearance, so special attention is needed during hand sorting. Once mixed into coffee, they bring a rotten odor.

5. Dead Beans

Beans formed abnormally. Their color does not easily change during roasting, so they are relatively easy to distinguish. They taste flat and, like silver skin, are harmful rather than beneficial, becoming a source of off-flavors.

6. Immature Beans

Beans picked before they mature have a fishy, unpleasant taste. Storing coffee beans for several years is precisely a measure taken to deal with these immature beans.

7. Shell Beans

They are produced by poor drying or abnormal hybridization; the bean splits from the center line, and the inner side flips out like a shell. Shell beans cause uneven roasting and are also prone to catching fire during deep roasting.

8. Insect-Damaged Beans

Moths invade and lay eggs when the coffee fruit ripens and turns red. The larvae eat the fruit as they grow, leaving insect-damaged marks on the surface of the beans. Insect-damaged beans make the coffee liquid cloudy and sometimes produce strange flavors.

9. Black Beans

Beans that mature earlier and fall to the ground, then ferment and turn black after long contact with the ground. They can be easily picked out through the hand-sorting step. Coffee brewed with black beans mixed in produces a rotten odor, and the liquid is cloudy.

10. Cocoa

The natural drying method leaves residual pulp and insufficient hulling, which are the reasons for its formation. It has iodine and earthy flavors, and also gives off an ammonia-like odor. In Portuguese, "cocoa" means "feces."

That concludes the full introduction to the top ten types of defective coffee beans. I believe everyone now has a basic understanding of these types of defective beans, which also lays the groundwork for the next article on how to select defective beans.

The above content is compiled by CoffeeHunters, a coffee news website.