From the coffee plant to the cup: a journey through the chemistry of coffee

Carmen Piras

Coffee is definitely one of the most popular and addictive drinks in the world. However, to obtain the coffee we drink from the plant, there are numerous steps in which the beans are extracted and treated to finally achieve the powder. Before we start our journey through the magic world of coffee, we will go back to the past to explore its history and find out how it arrived in Europe and became so popular.

 HISTORY

 Merchants

The word “coffee” comes from the Arabic word “qahwa”, originally used to describe a dark red beverage that was extracted from some seeds and caused exciting and stimulating effects. The turkish “kahve” came from this word, later the Italian word “caffè” and then “coffee”. According to the legend, the history of coffee began in the Ethiopian province of Kaffa, where a shepherd used to take his goats to graze. One day, he noticed that the goats, after eating the berries of the coffee plant, became more active and energetic. For this reason, he decided to roast the seeds of the plant and grind them to obtain an infusion. Coffee was probably subsequently exported by some slaves in Yemen and Saudi Arabia, where, in the fifteenth century, it started to be cultivated. Initially, Arabs banned coffee exportation; however in 1616 some Dutch merchants managed to bring some plants to the Netherlands, which could be cultivated in greenhouses. The Dutch began then to cultivate coffee plants in their colonies in India and Indonesia, from where coffee was exported to Europe by some merchants of Venice. From 1650, coffee was also exported to England, France, Germany and Austria. Nevertheless, it was from the ‘700 that coffee started to be grown on a large scale in the British and Dutch colonies, reaching in this way Central and South America, which currently holds the primate of world production (Colombia and Brasil). As coffee consumption was growing, the first coffee houses arose and diffused as meeting places for discussion and dissemination of political, literary and philosophical ideas. Important coffee houses were opened in Oxford, London, Paris, Vienna, Venice and Florence.

THE PLANT

coffee plant

The coffee plant, Coffea, belongs to the family of Rubiaceae, which includes over 6,000 species of small trees and shrubs. The mainly produced species are represented by: – Coffea Arabica (Arabica Coffee – about 60% of world production): cultivated in Latin America, India, Indonesia, Africa and Middle East – Coffea Canephora (Robusta Coffee): cultivated in West and Central Africa, Southeast Asia and Brazil – Coffea Liberica (Liberica Coffee): cultivated in Malaysia and West Africa – Coffea Dewevrei (Excelsa Coffee): cultivated in Africa.

 HOW IS COFFEE OBTAINED

 Due to its botanical characteristics, the coffee plant grows easily in mountain areas. Depending on the variety it takes up to 3 or 4 years for the plant to start to produce fruits, which are then collected by hand or by machine. Each fruit looks like a red berry similar to cherries and contains two seeds (coffee beans), which are removed from the fruit and dried before being roasted. This process can be performed in two ways:

1. Dry method: the whole fruit is dried under the sun on large concrete patios. This is the most important stage of the process, as it can affect the quality of the obtained green coffee. The dried cherries are stored in silos and subsequently sent to the mill where they are processed to remove the outer layers of the cherry and obtain the beans.

2. Wet method: in this case the pulp is removed from the cherry by a machine and it is placed in large fermentation tanks to remove coffee mucilage through enzymatic reactions. When the fermentation is completed, the coffee is then dried under the sun or with a mechanical dryer and finally stored. In both cases, before the coffee is ready to be exported and sold it passes through the final stages of “curing”, which involves a number of cleaning, sorting and grading operations.

ROASTING

 coffee beans

The roasting process is then fundamental to obtain all the aroma and flavors and it is crucial to produce a high quality coffee. This is done by heating the coffee beans to 180-240oC for 8-15 minutes in order to obtain the caffeol or coffee oil, which is the essence of coffee. The roasting process has to be carefully controlled to obtain a uniform resulting flavor. Coffee is then assessed for taste to create a flavor profile and evaluate its quality. This process is called “cup tasting” or “cupping“.

DECAFFEINATION

The decaffeination process is performed on green coffee beans to extract the caffeine from the beans. Four different methods can be applied for this purpose:

– Water method

– Ethyl acetate method

– Liquid CO2 method

– Methylene chloride method

All these methods involve some common steps:

  1. The caffeine is made available for extraction by swelling the green coffee beans or steaming
  2. The caffeine is extracted
  3. Solvent residues are removed from the beans by steam stripping
  4. The decaffeinated coffee beans are finally dried.

DIFFERENT WAYS TO MAKE COFFEE

 Moka

Depending on personal preferences, coffee can be prepared in different ways.

Espresso is one of the most common ways of making coffee. It was invented in Italy and it is made with specific machines which force hot water through ground, compacted coffee into the cups below. On top of the black coffee, lies a golden brown liquid called “crema” that can be used by an expert taster to judge the quality of the coffee. The Moka-Napoletana is another common way to make coffee in Italy and it combines the characteristic of espresso and the percolator made coffee. It works by boiling the water into a lower chamber and forcing it through the coffee which seats on a filter. A similar process is used by the Percolator, which works by heating the coarsely ground coffee and cold water until the water starts boiling and bubbles up in the top of the unit. A different way of making coffee is the Plunger/Cafetiere method, which works by placing the coffee and warm water into the pot. After few minutes the plunger is then pushed down to separate the infusion from the coffee grounds.

CHEMISTRY OF COFFEE: WHAT’S IN THE CUP?

 coffee cup

The most important active component of coffee is definitely caffeine. However, a huge number of chemical compounds and over 1000 aroma compounds are also contained in coffee.

Caffeine

  • Caffeine is an alkaloid that belongs to the family of xanthine (from the greek “xanthos”, yellow), which also includes theobromine and theophylline. The mechanism of action of caffeine can be re-conducted to its action as an antagonist of the adenosine A2A receptor, which is part of the class of purinergic receptors. This has a stimulating action on the central nervous system, on catecholamines release, on gastric acid production and on metabolism. The psychotropic effects include increased state of alert and ability to concentrate, improved physical and mental efficiency. By contrast, higher doses induce agitation, tremors, nausea, restlessness and diuresis.

Phenolic compounds in coffee

  • Coffee also contains numerous Phenolic Compounds, which represent 12% of the dry weight of green unroasted beans. These include: quinic acid, trans-cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, 4-O-caffeoylquinic acid, 3,5-O-caffeolquinic acid, 5-O-feruloylquinic acid, 3-O-caffeoylquinic acid. These compounds are responsible for the bitter taste of coffee, its brown colours and also its antioxidants properties.

 For more information: ico.org

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2 thoughts on “From the coffee plant to the cup: a journey through the chemistry of coffee

  1. Such an interesting article. I’m wondering about the effect that the coffee beans processing may have in the definition and character of a specific taste of coffee.

    Liked by 1 person

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