The Composition of Coffee Fruits and Coffee Beans: What Makes Coffee Bitter? Caffeine Content in Coffee Beans

Professional coffee knowledge exchange. For more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style).

Introduction

After reading the title, some friends might wonder: "Aren't coffee cherries and coffee beans the same thing?" Yes, the relationship between them is like that of a mother and son. Coffee beans come from the pit part of coffee cherries~

The Structure of a Coffee Cherry

This is a structural diagram of a coffee cherry. Looking from the outside to the inside, it is divided into seven parts:

1. Exocarp (outer skin)
2. Mesocarp (pulp)
3. Pectin layer
4. Parchment
5. Silver skin (thin film between coffee bean and parchment)
6. Endocarp (coffee bean)
7. Central line (embryo)

Exocarp

The exocarp consists of 1-2 layers of cells. Its structural characteristics are similar to biological epidermis, with a cuticle and stomata. When coffee cherries are unripe, the parenchyma cells of the exocarp contain many chloroplasts, which transform into chromoplasts when mature. Depending on the degree of ripeness, the outer skin of coffee cherries gradually changes from green to red.

Mesocarp

From a biological perspective, the coffee mesocarp belongs to part of the fruit skin, developed from the plant's ovary wall. The coffee pulp contains sugar and acidity, with a sweet fragrance like honeydew melon and clear, pleasant fruit acidity.

Pectin Layer

The coffee pectin layer consists of heteropolysaccharides between the pulp and the endocarp (parchment), with a sticky texture and difficulty dissolving in water. The pectin part is the highest sugar content component in coffee cherries and is an important part of coffee processing fermentation. For example, in honey processing, the more pectin retained, the more obvious the fermentation sensation of the coffee beans, and the sweetness will also be more pronounced.

Parchment

The parchment is composed of parenchyma cells and serves to protect the coffee beans.

Silver Skin

A very thin film between the parchment layer and the coffee bean, belonging to the cytoplasmic membrane.

Endocarp (Coffee Bean)

This is the seed of the coffee tree. Typically, one coffee cherry contains two coffee beans. Because the contacting surface is flat, they are called flat beans. In some cases, during the growth process, one coffee bean develops poorly, allowing the other to have sufficient growth space, presenting an elliptical shape, so they are called peaberries.

Embryo

The split in the middle of the coffee bean belongs to the embryo part. After breaking through the coffee seed coat, it develops into leaves and stems.

Composition of a Coffee Bean

After processing and drying, the moisture content of a green coffee bean will be within 13%. The moisture in coffee beans does not significantly affect the aroma and taste of coffee. Instead, what affects the coffee flavor is the proportion of waterless compounds hidden within the coffee beans. So what waterless compounds does a green coffee bean contain?

Polysaccharides

Polysaccharides are the most abundant component in coffee beans, accounting for about 35%-45%. They form the basis of substances like plant fibers, are insoluble in water, have no sweetness, and do not directly affect coffee flavor. The coffee grounds remaining after brewing are composed of polysaccharide fibers. There is no significant difference in the proportion of polysaccharides between Arabica and Robusta coffee beans.

Proteins

Coffee beans contain 12% protein. Like polysaccharides, proteins do not directly affect coffee flavor. There is no significant difference in the proportion of proteins between Arabica and Robusta coffee beans.

Lipids

The lipids in coffee beans are composed of oils such as linoleic acid and palmitic acid. The lipid content in Arabica coffee beans is 20%, while in Robusta coffee beans it is 10%. Because many aromatic fatty carboxylic acids (including citric acid, malic acid, acetic acid, lactic acid, and formic acid) can dissolve in lipids, the amount of lipids in coffee determines the richness of flavor after tasting.

Oligosaccharides (Sucrose)

The amount of sucrose in coffee beans determines the quality of coffee flavor. The higher the sucrose content, the better the coffee tastes. The sucrose content in Arabica coffee beans is 6%-9%, while in Robusta coffee beans it is 3%-5%.

Chlorogenic Acid

The chlorogenic acid in coffee beans is an undesirable acid that feels astringent and unpleasant. Through roasting, chlorogenic acid degrades into quinic acid. Quinic acid is a phenolic acid, non-volatile, so it cannot be detected by smell, but it tastes bitter and is one of the sources of bitterness in dark-roasted coffee. The chlorogenic acid content in Arabica coffee beans is 5%-8%, while in Robusta coffee beans it is 7%-11%.

Other Organic Acids & Inorganic Acids (Phosphoric Acid)

Besides chlorogenic acid, the total content of citric acid, malic acid, acetic acid, lactic acid, formic acid, and phosphoric acid accounts for at most 2% in both Arabica and Robusta coffee beans.

Amino Acids

The amino acids in green coffee beans include aspartic acid, leucine, etc., accounting for at most 2% in both Arabica and Robusta coffee beans.

Caffeine

The caffeine content in coffee beans is closely related to coffee variety and growing altitude. The caffeine content in Arabica varieties is about 0.9-1.4%, while in Robusta varieties it generally ranges from 2%-3%. Different Arabica varieties planted in different regions may also have slightly varying caffeine content.

For more specialty coffee beans, please add FrontStreet Coffee on private WeChat, WeChat ID: kaixinguoguo0925

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473