Anatomical Structure Of Coffee Fruit

Vietnamese Coffee Exporter

The structure of the coffee fruit has two parts, the rind (with the outer skin + mucilage) and the seed (including the husk, silk skin, and coffee bean). These are the basic concepts that will help you understand why wet processing produces higher quality coffee than dry processing. The physicochemical changes, when roasting coffee or the knowledge of coffee extraction … important and basic is the key! Let’s learn more about the features of each part with Helena through this post.

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Ripe coffee cherries cut horizontally

Structure of coffee beans fruit

Coffee Cherry

It is well known that the “coffee” that we roast, grind, and the brew is the seed of a fruit. The coffee tree produces the coffee fruit, and the coffee beans are inside the fruit. Looking from the outside in, coffee cherries will essentially include: Crust outermost ( outer skin ), the pulp ( Pulp ), class husk ( Parchment ), crust silk ( silver skin ), and human ( bean ). These structural classes can be divided into two main parts, including:

  • Skin: Including the outer shell ( exocarp ) and the fleshy shell ( mesocarp ).
  • The seed part (Bean): Consists of the endocarp ( endocarp ), the silver skin, and the kernel containing the endosperm ( Endosperm ) and the embryo ( Embryo ).
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The skins of a coffee fruit

In some documents, the structure division may be different such as The shell will include three components: the outer shell ( exocarp ), the fruit pulp ( mesocarp ), the husk ( endocarp ); eanwhile, the seed only includes Silk skin ( Silver Skin ) and coffee bean ( bean ).

Shell (exocarp & mesocarp)

The outer shell ( exocarp ): That’s the outermost surface of the coffee fruit, is formed by a layer of small parenchymal cells (cells containing chloroplasts primary and has the ability to absorb water). The color of the pods at the beginning of formation is green due to the presence of chloroplasts then disappears as the fruit ripens. The color at maturity depends on the coffee variety, but the most common are red or yellow. The red skin color ( Typica Coffee ) comes from anthocyanin pigments, while the yellow color is attributed to luteolin ( Bourbon coffee).

Beneath the outer skin, the mesoderm layer ( mesocarp ) is often called the pulp ( pulp ). Mucilage (or mucilage ) is the inner layer of the pulp, in addition to a layer of pectin below the mucous membrane, these layers contain a lot of sugar, which is important in the fermentation process

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Cross-cut a regular coffee – with two kernels
Cross-cut Peaberry– only one

In unripe coffee fruit, the mesocarp is the hard tissue attached to the outer skin of the coffee fruit, when the fruit matures, pectolytic enzymes break down the pectic chains to form sugar and pectin compounds that give a soft structure, succulent has a high viscosity so it is often called mucilage. In wet processing, this mucilage is removed through controlled fermentation. Meanwhile, with the dry processing technique, the mucilage along with the outer shell is preserved during the drying process.

Note about ‘pull’ and ‘mucilage’

In fact, there are not many such “shells” around the coffee beans and it is difficult to distinguish which cell type of an exocarp or a mesocarp. So ” pulp ” or ” mucilage “, pulp or mucus all look the same and produce what we call a coffee berry (according to Emma Sage, CQI’s).

After the coffee cherries have been cleaned off the skin, pulp, and mucilage by dry or wet processing, the green coffee beans can be traded in the international market. These beans are still covered by the husk (which is sometimes removed) and their thin, silvery skin. In another (optional) polishing step, this silver coating can also be removed and ready for roasting.

A layer of husk ( Parchment ):  the outermost layer of the grain, in direct contact with the peel, Parchment is formed from three to seven cell layers sclerosis (hair cells play a major role in the plant) should Also known as rice husk. The cells constituting the husk will harden during the maturation of the coffee fruit, thereby limiting the final size of the coffee bean. In Arabica coffee, the average weight of the husk with a moisture content of approx 11% is within 3.8% of the total weight of the coffee fruit (Wilbaux, 1961, as cited in Borém, 2008).

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The husk of a fresh coffee bean (part of the husk can be seen on the bean)

Silk shell ( silver skin ):  The pericarp is composed of a large amount of fiber (56-62%), with silver-white after drying, so-called silver casing. This shell is very thin and can be removed from the kernel during the polishing process. However, some coffee processors often leave silk on the beans as a natural protective layer, which will then self-destruct during the roasting process.

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Silk skin (Silverskin) peels off the seeds after roasting

During the roasting process, the beans expand and this thin skin separates, becoming a by-product of the coffee roasting industry. Silverskin – compared to other coffee by-products, is a relatively stable product due to its lower moisture content (5–7%). It is currently being used for fuel, composting, and soil fertilization, or mined for cosmetic and pharmaceutical purposes.

Coffee filling

Coffee grounds

When referring to the coffee bean – also referring to the endosperm ( Enosperm ), this is the most important part of the coffee fruit, responsible for the accumulation of nutrients for the germination of the embryo. A regular coffee fruit has 2 kernels (especially 1 or 3). The chemical composition of the kernel is extremely important as it is considered the precursor to the later flavors and aromas in roasted coffee.

The chemicals detected in the endosperm can be classified as either soluble or insoluble in water. Water-soluble compounds such as caffeine , trigonelline, nicotinic acid (niacin), organic acids ( chlorogenic acid alone has about 18 isomers), carbohydrate components. Water-insoluble components include cellulosepolysaccharideslignin, and hemicellulose, as well as a number of proteins, minerals, and lipids.

Because the embryo is inside the endosperm, some documents refer to both as endosperm, and after roasting you can hardly distinguish the components. this part. They become noticeable when the seed begins to germinate – then the embryonic axis ( hypocotyl ) will elongate and push the seed above the ground. The initial cotyledons will be underground as soon as new cotyledons will form.

Crossing a coffee bean

The article, with many scientific concepts and terms, is “relatively difficult to understand”, but this knowledge will help you better understand the production, processing, and roasting process. The next time you choose between naturally dry and wet-processed coffee, you can be more confident knowing what that means and the impact it will have on your cup. For further research into coffee, you should take a look at the chemical composition of coffee beans.

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