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History And Properties Of Coffee (III)

Continuing with the theme of the history of coffee, today we will tell you all about the beans and the process that is followed until the coffee infusion is reached.


Arabica and Robusta Coffees.

Coffee beans are the seeds of two tropical species, relatives of the gardenia. Coffea arabica, a 5-meter-tall tree native to the highlands and cool regions of Ethiopia and Sudan, produces the beans known as “Arabica”; and Coffea canephora, a larger tree native to the warmer and more humid areas of West Africa, produces “Robusta” beans.

Approximately two-thirds of the beans in the international market are Arabica, which develop a more complex and balanced flavor than Robusta. They contain less caffeine (less than 1.5% of the weight of the dry bean, compared to 2.5% in Robusta), less phenolic material (6.5% compared to 10%), and more oil (16% compared to 10%) and sugar (7% compared to 3.5%). Robusta varieties did not gain prominence until the 19th century when their disease resistance made them important in Indonesia and other parts.

Dry and Wet Processing.

To prepare coffee beans, ripe berries are harvested from the trees, and the seeds are separated from the pulp using one of two basic methods. In the dry method, they are piled up to ferment for a few days and then spread out in the sun. Afterward, the fruits are separated by machine.

Drying Coffee Seeds

In the wet method, most of the pulp is removed from the seeds by machine rubbing, and the rest is liquefied with a day or two of microbial fermentation. The seeds are then washed in plenty of water, dried until they contain only 10% moisture, and the adhesive inner “husk,” which resembles parchment, is mechanically removed. As a result, the seeds lose some sugars and minerals, and that’s why they tend to produce coffee with less body and more acidity than seeds processed in the dry method. However, they often have a more aromatic profile, and their quality tends to be more consistent.


Green and raw coffee beans are as hard as corn kernels and roughly as flavorful. Roasting transforms them into fragile flavor packets that are easy to unlock. Most people leave the roasting process to professionals, but roasting coffee at home can be a fascinating experience, as cooks in many countries have done for a long time. They continue to do so with equipment ranging from a pan to special toasters, including popcorn machines.

Roasting Coffee in a Pan

Coffee beans are roasted at temperatures between 190 and 220°C (374-428°F), and the process can last from 15 to 90 minutes. As the temperature of the beans approaches the boiling point of water, the small amount of moisture inside the cells turns into vapor and swells the beans to one and a half times their original volume. Then, at increasingly higher temperatures, proteins, sugars, phenolic materials, and other components begin to break down into fragments that react with each other and develop the brown pigments and typical aromas of Maillard reactions. At around 160°C (320°F), these reactions continue, much like a candle flame, and the extreme molecular breakdown produces more water vapor and gaseous carbon dioxide, with production increasing significantly at 200°C (392°F). If roasting continues, oil begins to escape from the damaged cells to the surface of the bean, providing a visible shine.

When the beans have reached the desired level of roasting, they are immediately cooled with cold air or sprayed with water to stop the molecular breakdown. The result is a brown, brittle, spongy bean with its sponge pores filled with carbon dioxide.

Development of Coffee Flavor.

The more the bean is heated during roasting, the darker it becomes, and its color is a good indicator of flavor balance. In the early stages of roasting, sugars break down into various acids (formic, acetic, lactic) which, along with their own organic acids (citric, malic), give lightly browned beans a pronounced acidity. As roasting continues, both the acids and astringent phenolic materials (chlorogenic acid) are destroyed, reducing acidity and astringency. However, bitterness increases because some products of browning reactions are bitter. And as the bean color darkens beyond medium brown, the distinct flavors characteristic of high-quality beans are overtaken by more generic roasted flavors—or conversely, the deficiencies of second-class beans become less obvious. Finally, when acids, tannins, and carbohydrates have diminished, the resulting infusion will have less body, as there are fewer compounds to stimulate our palate. Medium roasts provide the best body.

  • Effects of Roasting on Coffee Beans
  • Weight Loss in Roasted Coffee Beans

Roasting LevelWeight Loss, %
Cinnamon (190ºC)12, mostly moisture
Full City16, half moisture and half solids
Italian (220ºC)18-20, mostly solids

  • Composition of Raw and Roasted Coffee Beans, Percentage by Weight

Phenolic Compounds63
Large Aggregates Contributing Color and Body025

Coffee Storage.

Once roasted, coffee beans can be reasonably well-preserved for a couple of weeks at room temperature, or a couple of months in the refrigerator, before becoming noticeably stale. One reason whole beans keep for so long is that they are filled with carbon dioxide, which helps exclude oxygen from the porous interior. When the beans are ground, they only last a few days at room temperature.

Grinding Coffee.

The key to properly grinding coffee is to achieve a fairly consistent particle size appropriate for the brewing method. The smaller the particle size, the greater the surface area exposed to water, and the faster its contents will be extracted. If the particle size is too variable, it will be challenging to control extraction during brewing. Small particles can become overly extracted, and large ones under-extracted, resulting in a bitter and weak brew. A typical blade grinder pulverizes all pieces until the machine stops, no matter how small the pieces, so coarse and medium grinds will contain some fine powder. However, more expensive burr grinders allow small particles to escape through grooves in the crushing surfaces, providing a more uniform particle size.

Coffee Brewing.

Brewing involves extracting and passing through water the desirable substances from the coffee bean, in quantities that produce a balanced and enjoyable beverage. These substances include many aromatic and flavorful compounds, as well as brown pigments that contribute color (almost a third of the total extract) and carbohydrates from cell walls that contribute body (about another third).

The flavor, color, and body of the resulting beverage depend on the amount of ground coffee used for a given volume of water and the proportion of that coffee that is extracted into the water. Insufficient extraction will result in a watery and acidic infusion if the grams haven’t been ground well and the flavor remains in the particles, if the contact time between the coffee and water was too short, or if the temperature was too low. If it has been ground too fine, or the contact time is too long, or the temperature too high, over-extraction will occur, and the beverage will be rough and bitter.

The ideal temperature for any type of coffee falls between 85 and 93°C (185-200°F). If it’s higher, bitter compounds will be extracted too quickly. For a regular cup of American coffee, the usual brewing time varies from one to three minutes if the grind is very fine or from 6 to 8 minutes if the particles are coarser.

  • This table summarizes the most important features of the most common coffee preparation methods and the types of infusion they produce.

MethodGrind SizeInfusion TemperatureInfusion TimeExtraction PressureFlavorBodyInfusion Stability
Middle EasternVery Fine (0.1 mm)Up to 100ºC10-12 min1Full but bitterFullLow
Drip Coffee MakerCoarse (1mm)82-85ºC5-12 min1Smooth, sometimes bitterLightGood
Manual Pour OverMedium (0.5mm)87-93ºC1-4 min1FullLightGood
French PressCoarse (1mm)100ºC3-5 min1(+)Full, sometimes bitterLightGood
AeroPressCoarse (1mm)87-90ºC4-6 min1(+)FullMediumGood
Moka PotMedium (0.5mm)110ºC1-2 min1.5Full but bitterFullNormal
Espresso (Steam)Fine (0.3mm)100ºC1-2 min1(+)Full but bitterFullLow
Espresso (Pump)Fine (0.3mm)93ºC0.3-0.5 min9Very completeVery fullLow

What did you think of this new entry? We can’t wait to tell you all the coffee infusion methods! But you will have to wait for the next one… ????


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