Coffee

What it is

Of the two main species grown, arabica (from C. arabica) and robusta (from C. canephora), about three-quarters of the coffee cultivated worldwide is C. arabica. Arabica coffee is generally more highly regarded than robusta coffee. Robusta coffee tends to be bitter and has less flavor but a better body than arabica. The fruit of Coffea arabica is a drupe that typically contains two seeds, which become coffee beans. Robusta strains contain about 40-50% more caffeine than arabica.

Aroma chemistry

The number of aromatic compounds found in coffee is well over 800. The perception of coffee aroma depends on both the concentration of a compound and its odor threshold. A relatively small group of compounds with a high concentration and a low odor threshold probably makes up the fragrance known as coffee aroma. The Maillard reaction is one of the chemical processes that affect the development of volatile compounds in coffee, alongside the degradation of amino acids, trigonelline, sugar and phenolic acids. The Maillard reaction is a chemical reaction between amino acids and reducing sugars that creates melanoidins, the compounds that give browned food its distinctive flavor. The Maillard reaction typically proceeds rapidly from around 140 to 165 °C.

2-Furfurylthiol, also called furfuryl mercaptan, is an organosulfur compound. 2-Furfurylthiol is a colourless liquid with a strong odour of roasted coffee and a bitter taste. It is a key component of the aroma of roasted coffee. The odor of 2-furfurylthiol is described as roasted coffee, caramel, sulfurous and waxy. 2-Furfurylthiol has a perception threshold of 0.1 μg/L in hydroalcoholic solution. 2-Furfurylthiol has the CAS number 98-02-2. Sulfur-containing amino acids are generally accepted as key precursors and sources of sulfur in the formation of 2-furfurylthiol, by reaction with sugars. In a model system, pentoses or hexoses and L-cysteine can produce 2-furfurylthiol by way of furfural and H₂S.

Furans are the most predominant group of compounds among the coffee aromatics. Furans typically have caramel-like odors because they result from the pyrolysis of sugars. Pyrazines are the second most abundant class of aromatic compounds in coffee and contribute roasted, walnut, cereal, cracker or toast-like flavors. Pyrazines and thiazoles have the lowest odor thresholds and therefore contribute significantly to the coffee aroma. Pyrroles are responsible for some of the sweet, caramel-like and mushroom-like aromas in coffee. Thiophens are known to have a meaty aroma. Guaiacol is described as phenolic and spicy, and 4-vinylguaiacol as spicy. Furaneol is described as caramel-like.

Roasting

Roasting is initially endothermic, but at around 175 °C it becomes exothermic. During roasting, coffee beans lose 15 to 18% of their mass, due mainly to the loss of water but also of volatile compounds. Caffeol, one of the oils that develop during roasting, is created at about 200 °C and is largely responsible for coffee's aroma and flavor. Light roasts are lighter-bodied and higher in acidity, and can contain grassy or fruity notes. As the beans darken to a deep brown, the origin flavors are eclipsed by the flavors created by the roasting process. In dark roasts, full-bodied and bittersweet flavors are prominent and little origin character remains.

Caffeine, a stimulant of the methylxanthine class, is found in the coffee bean, the seed of the Coffea plant. Caffeine remains stable up to 200 °C and completely decomposes around 285 °C. The caffeine content of a coffee is not likely changed much by the roasting process.

Forms in perfumery

Coffee absolute belongs to the gourmand olfactive family. One coffee absolute has a shelf life of 12 months. Coffee CO2 extract is a viscous liquid ranging from light to dark brown, with the characteristic aroma of roasted Arabica and Robusta coffee.