Coffee: cultivation, roasting and preparation - the science


The word coffee is derived from the Turkish kahve, which in turn is derived from the Arabic qahwa (قهوة). The root of the word indicates the meaning, it stands for "stimulating drink", but can also be translated as "intoxicating" or even "wine". This means that even a very long time ago, people in the Near East knew that a coffee drink had a psychotropic effect, even though the ingredient caffeine could not yet be defined. But even the Arabs and Turks knew that the degree of roasting and grinding influenced the effect. The quality of coffee beans was also known many centuries ago. Even ethymologically (linguistically) the connections are recognizable. The Arabs call the best coffee beans bunn (بن), they in turn derived this word from the even much older language Amharic, where they use bunaa (ቡና) is called.

Coffee cultivation

Coffee beans come from the plant family Rubiaceae. The variety of species is diverse, but practically only these varieties are available on the market:

Kopi Luwak is not a botanical variety, however, but is obtained from beans that cats have previously half-digested. There is another variety of this species, Kape Alamid, but it is of little importance. Maragogype is a cross between Arabica and Liberica plants. Arabica and Robusta dominate the market in absolute terms with a combined share of 98%, with Arabica accounting for two-thirds of this share. In addition to those mentioned, there are 124 wild coffee species that have never been cultivated. 60% of them are considered endangered. Targeted coffee cultivation is carried out in more than 50 countries, mainly by smallholders. The main coffee growing countries and regions are:


  • Latin America
  • East Africa
  • Papua New Guinea
  • India


  • West Africa
  • Uganda
  • Vietnam
  • Indonesia
  • India
  • Brazil

Coffee bushes produce their first yields after three to four years, but these dwindle after around 20 years. The ideal climate for coffee cultivation is characterised by few temperature extremes. Temperatures should almost never exceed 30 °C, rarely fall below 13 °C and ideally average 18 - 25 °C. The plants die in frost. Frost causes the plants to die. The optimum annual rainfall would be 1,500 - 2,000 millimetres; from 800 - 1,000 millimetres, coffee cultivation only works with additional irrigation. Below 800 millimetres it is not worthwhile. There are also certain requirements for the soil and shading. Ideal cultivation areas lie between 300 and 1,200 metres above sea level. Arabica coffee grown in the highlands is considered to be of particularly high quality. The planting of new coffee bushes is done by scattering seeds or also by cuttings. The seeds must first sprout in plant nursery beds for six to eight weeks before coffee farmers can plant them in a plantation. Since coffee bushes actually need shade, but thus grow more slowly, with the beans in turn achieving a much higher quality, coffee farmers have a choice: they can keep the natural methods, but then harvest slightly less, albeit with higher quality. They can also clear forests, grow coffee in the blazing sun and support its growth with lots of fertilizer, using pesticides to combat the increased pests. In the process, they harvest faster and more, but of lower quality and with increased environmental impact. Sun coffee very often requires supplemental irrigation, and the clearing of forests for the benefit of coffee plantations is even considered a climate killer. When western consumers buy organic coffee, they support the original, natural coffee cultivation. Fair trade coffee, on the other hand, guarantees that coffee cultivation does not involve child labour, which is considered a major problem in this industry.


To roast coffee, the coffee beans are dry and heated under normal pressure. Roasting is a Maillard reaction, as occurs in frying and deep-frying: amine compounds in the coffee bean, including amino acids, proteins and peptides transform into new compounds through chemical reduction. Roasting of coffee starts at 60 °C, it ends at 200 to 250 °C on the surface of the bean, depending on the desired degree of browning. The ambient temperature is higher, and it depends on how gently the roasting is done. The industrial roasting process with very high ambient temperatures (up to 550 °C) is fast, but this coffee tastes less good than that made from beans where the roasting was done gently in a drum. Roasting is very crucial to the aroma development and wholesomeness of coffee. The fast, hot industrial roasting can even produce harmful substances such as acrylamide and melanoidins, which are also warned against when frying French fries, for example, too hot. There are different degrees of roasting:

  • Cinnamon roast (very light)
  • American roast (medium)
  • Viennese roast (relatively strong)
  • French roast (double)
  • Spanish roasting for the Café torrefacto (roasting with added sugar)
  • Italian roasting for espresso

Coffee beans for espresso require darker roasting, but this alone does not make espresso. The preparation is also important for espresso. It requires a certain brewing pressure (6 - 9 bar) in the espresso machine and is brewed in 25 - 30 seconds, whereas filter coffee takes up to six minutes to brew. Espresso also contains significantly less water and is characterised by its crema. The degree of acidity can also be influenced by the roasting process. Chlorogenic acid in the beans may upset the stomachs of some coffee connoisseurs, but there are even roasts for espresso that are particularly low in acid. Of course, the acidity also contributes to the taste, which is why it should not disappear completely. Basically, acidity depends on the type of coffee and the growing conditions of the beans, as well as the roast. Arabica is generally somewhat less acidic, roasting for espresso also removes a lot of acid if it is done a little longer and gently at the same time. Well-stocked coffee retailers offer such espresso and other low-acid varieties.

The right coffee preparation

Especially for low-acid coffee enjoyment, the preparation is important. In general, the shorter the contact between the water and the coffee grounds, the lower the acidity of the coffee drink. This is most likely to be achieved with a portafilter machine. This mainly extracts the aromas, but not the acidic substances. The brewing temperature should not be 100 °C, but 92 - 96 °C. Acids in coffee beans are:

  • Chlorogenic acid with a strong influence on the taste, but also valuable as a natural antioxidant.
  • phosphoric acid, which intensifies sweetness
  • citric acid, mainly in Arabica beans from high altitudes, which produces a fruity note
  • Malic acid, which makes the taste reminiscent of fruit
  • Tartaric acid for a slight sharpness to spiciness
  • Acetic acid for a lime-like aroma

In addition to preparation in a portafilter machine, there are variants of filtering, in which hot water runs relatively slowly through the coffee grounds, infusing ("Turkish"), and boiling in an espresso machine. But these are only the most common preparation methods. The French Press and the new Aero Press (combination of French Press and filtering) are also possibilities, and there are many more.

Coffee: History

The coffee plant first grew wild in Africa. Muslims like to tell the legend that their prophet Mohammed was once seduced into drinking coffee by the archangel Gabriel. Another legend, which itself dates back to the 17th century, attributes the discovery of coffee beans to Ethiopian or Yemeni shepherds whose goats ate coffee beans and were then very lively, which led the shepherds and monks who befriended them to make coffee. The Ethiopian region of Kaffa is also thought to be the area of origin of the first coffee plants discovered. The discovery is said to have taken place around the 9th century, which would not fit the legend of the Prophet Mohammed, as he was probably born around 570. From Ethiopia, coffee beans and plants were probably exported to Yemen and on to the Arabian Peninsula from the 14th century onwards. An early trading centre was probably the Yemeni port city of Mocha (Mokka, today al-Mukha). The preparation of mocha after prior roasting probably only became established over the course of centuries. From the 16th century onwards, coffee houses sprang up in the Ottoman Empire, Persia and Syria, but at times the consumption of coffee was banned again. The drink probably arrived in Europe in the very early 17th century, but it was already known to some Europeans from their travels in the Orient about 100 years earlier. In the 17th and early 18th centuries, however, cafés were established in all the major European cities. One of these café houses was called "Zum Arabischen Coffe Baum", it opened in Leipzig in 1711 and operated there until 2018, making it the oldest of its kind in Germany. It has since become just a coffee museum. Johann Wolfgang von Goethe, who was very interested in science, later suggested distilling the coffee beans, which was implemented by chemist Ferdinand Runge, who discovered caffeine. From the 17th century onwards, the Dutch, and later also the French and Portuguese, had coffee plants cultivated in their colonies, which gradually led to the creation of the present-day coffee-growing areas. The coffee trade was nationalised in many places from the 18th century onwards. The Prussian King Frederick the Great, for example, banned private trade in 1766 and even private bean roasting from 1781, which in turn led to the flourishing smuggling of coffee beans. Frederick the Great employed former French soldiers as "coffee investigators" as secret police to control the trade, strolling through the streets and sniffing out whether anyone was secretly roasting coffee beans or even brewing the beverage. Prohibition, on the other hand, did nothing but encourage smuggling, which is why the ban and the associated state coffee monopoly were lifted again in Prussia from 1787. Drinking coffee promoted culture, but for a long time it also remained controversial because it was considered to be as intoxicating as the (then rather moderate) consumption of alcohol. Johann Sebastian Bach warned against it in his coffee cantata, but other artists (besides Goethe, for example, Lessing, Honoré de Balzac and Ludwig van Beethoven) praised the stimulating drink. Beethoven counted out exactly 60 coffee beans a day for a cup of mocha. There were also fierce opponents of the coffee habit. In the 18th century, King Gustav III of Sweden wanted to prove that it led to death by poisoning, so he pardoned a prisoner sentenced to death on condition that he either confirm or disprove this assumption by drinking coffee every day. The prisoner survived the king and also the doctors supervising the experiment.