Knowledge | Classification of defective beans

If too many defective beans are mixed into coffee roasting, the color of the finished product will be mottled. Compared with normal beans, defective beans oxidize very quickly and sometimes turn white after baking. Cheap coffee beans are often sold in stores such as supermarkets or coffee shops. if you open those packages, you can find that there are a lot of uneven roasted beans, all as a result of omitting the step of manual selection and direct baking.

Classification of defective beans

Black bean

The appearance is opaque black, according to the black part of the whole coffee bean is divided into total black and local black beans. When the black area is less than 50% of the bean body, it will be treated as a local black bean, otherwise it will be treated as a full black bean.

Cause: insufficient water supply of coffee fruit during ripening period, affecting plant metabolism or picking immature beans are dried at high temperature (more than 30 degrees Celsius)

Effect on flavor: it can produce uncomfortable fermentation or odor, dirty, moldy, sour and phenolic smell.

Harm: octreotide A, which can harm the liver and kidneys, although some scholars have reported that 80% of the toxins will degrade after baking (200 degrees Celsius), pick them out as much as possible.

Sour bean

The appearance color is a little similar to yellowish brown or reddish brown, and sometimes it is easy to mix with the color of silver skin in sun beans, which is more difficult to identify. It is usually black at the endosperm point (where the arrow points), and the acid choking smell of acetic acid can be smelled when the beans are cut. Sour beans are divided into two categories: total sour beans and local sour beans, the difference is similar to black beans, if less than 50% of the beans belong to local sour beans, otherwise they are all sour beans.

Cause: the main cause of sour bean is excessive fermentation. If the environment around the coffee is relatively humid, the ripe coffee fruit will ferment too much if it is not picked in time on the tree; if the picked coffee fruit is stored for too long and not treated in time, it will also be overfermented; the fermentation pool will be dirty in washing, or dirty with water will also cause sour beans; when drying, if the coffee fruit dries slowly, coupled with improper stacking, it will also cause excessive fermentation of coffee fruit and form sour beans.

Effect on flavor: the over-fermented sour taste is disgusting.

Moldy bean

The color of moldy beans is a bit like sour beans, yellow or reddish brown, but an obvious difference is that moldy beans will have a small dent, a little white powder in the spot, these powders are mold spores, very easy to interfere with other raw beans.

Cause: moldy beans may be caused by planting and post-treatment. The mold that causes moldy beans may breed and infect raw coffee beans under certain temperature and humidity conditions.

Effect on flavor: moldy soil flavor, phenol flavor. Cat Ye felt that the smell of miscellaneous soil in his mouth was more obvious, similar to eating a bad melon seed, and the obvious rough gravel and bitter taste in his mouth. Like black beans, there is a risk of the physiological virus of octreotide A.

Foreign object

Large foreign objects are relatively easy to distinguish from the appearance, but such as pebbles are generally difficult to quickly identify from raw beans, only with the help of auxiliary equipment to remove impurities to avoid the impact on the roaster and bean grinder.

Cause: foreign matter may be introduced into beans at all stages of the treatment process (mostly due to human reasons).

Effect on flavor: some foreign substances will affect raw beans and cause defective taste in the cup.

Moth-eaten bean

Small holes can be found in the appearance of worm-eaten beans, and because worms usually have holes on both sides, serious wormholes sometimes form several small holes. and like broken beans, because the bean body is damaged, it is easy to oxidize and become infected with mold in the worm-eaten area.

Cause: worm-eaten beans are produced in the process of planting. The coffee beetle will drill into the coffee beans to lay eggs, and then the eggs will parasitize in the coffee beans and absorb the nutrients of the coffee beans. Wormholes in wormeaten beans usually appear in pairs (in and out).

Effects on flavor: dirty, sour, phenolic and moldy.

Unripe bean

The remarkable feature of unripe beans is that the silver skin is tightly attached. Unripe beans are usually smaller than normal raw beans, with concave bodies and sharp edges.

Cause: unripe beans are produced in the process of planting, such as improper picking and planting late-ripening coffee varieties at high altitudes.

Effect on flavor: grass flavor, straw flavor.

Shrunken bean

Shrunken beans are smaller than normal beans, and most notably have dehydrated wrinkles, similar to raisins.

Cause: shrunken beans are only produced in the process of planting, mostly due to the stunted development of coffee trees caused by drought, unable to transport the necessary nutrients to the coffee fruit.

Effect on flavor: slight grass flavor, straw flavor.

Shell bean

Shell beans have two parts, the outer part is commonly known as "shell" shape, and the inner part is either tapered or cylindrical.

Cause: it is now believed that shell beans are mostly caused by variety genes, which are common in Kenyan SL28/SL34 varieties.

Effect on flavor: choky taste (because of the low density of shell beans, it is very easy to be scorched or even burned at high temperature during baking.

Shelled bean

Shell beans are generally covered in whole or in part with parchment shells, and the appearance (shell) is khaki.

Cause: mainly in the process of peeling after drying, if the peeling machine aging or improper training will cause shelled beans to leak.

Effect on flavor: woodiness. (if there is a large proportion of shell beans, the woody flavor will be obvious.)

Coffee raw beans are the most important factor affecting the flavor, so for a good cup of coffee, defective beans must be removed, which can not only ensure the stability of roasting, but also the most effective guarantee of coffee fault tolerance.