Several kinds of coffee defective beans are introduced.

Moldy beans: because of incomplete drying, or damp in the process of transportation and storage, cyan and white molds grow, which sometimes make the beans stick together. If these moldy beans are not removed, they will produce moldy smell.

Dead beans: beans with abnormal results. The color is not easy to change because of baking, so it is easy to distinguish. The flavor is thin, as harmful as silver skin, and will become a source of peculiar smell.

Immature beans: beans picked before they are ripe have a fishy, disgusting taste. Leaving raw coffee beans for years is a strategy to deal with these immature beans.

Shell beans: produced by poor dryness or abnormal mating; the beans break from the central line and the inside is turned out like a shell. Shell beans can cause uneven baking and are easy to catch fire during deep baking.

Moth-eaten beans: moths invade and lay eggs when the coffee fruit is ripe and red, and the larvae eat the coffee fruit and grow, leaving traces of moth on the surface of the beans. Worm-eaten beans can cause the coffee liquid to be cloudy and sometimes produce a strange smell.

Black beans: beans that mature early and fall to the ground and ferment and blacken when they come into contact with the ground for a long time. It can be easily removed by hand-selected steps. Coffee mixed with black beans will smell rotten and cloudy.

Over-dried beans (cocoa): it is caused by natural drying that the pulp remains and is not fully shelled. With iodine flavor, soil flavor and other flavor, it will give off a bad smell.

Shell beans: endocarp covers the inside of the pulp of coffee beans and remains on the washed coffee beans. The poor heat permeability when roasting and sometimes burning is the reason for the astringent taste of coffee. Others include broken beans, red peel beans (beans that rain naturally and taste dull), stunted beans (small grains of beans that stop growing due to lack of nutrients, strong flavor), and sometimes mixed with corn or pepper, and so on.

Stone: beans harvested are easily mixed with stone or sawdust because of natural drying.