What smells of coffee?
Coffee - a drink made from fried seeds (grains) of several plant species belonging to the genus Coffee (Coffea) of the family Marenovye (Rubiaceae).
There are more than 90 species of plants belonging to the genus of coffee (Coffea). There are two main types of coffee trees used on an industrial scale and, accordingly, grains obtained from the fruits of these trees: Coffea arabica L. - Arabica and Coffea canephora Pierre ex Froehn., Or Robusta, which is sometimes called Congolese coffee. According to various estimates, these two types account for up to 98% of the coffee produced. This volume is divided in the ratio of 70% - arabica, 30% - robusta. Other types of coffee account for only 2% of world production. The most common variety of coffee, arabica, grows at an altitude of 900 to 2000 meters above sea level. The grains, as a rule, have an oblong shape, a smooth surface, a slightly curved “S” letter line, in which usually after light roasting unburned particles of coffee berries remain. Robusta species is fast-growing and more resistant to pests than Arabica, and grows from about 0 to 600 m above sea level, primarily in tropical regions of Africa, India and Indonesia. The grains have a rounded shape, color - from light brown to grayish green. Robusta is generally considered less refined in terms of aroma. At the same time, it contains more caffeine, and is also often used in espresso blends, which allows you to achieve better coffee foam and cheapens the mixture.
In specialized stores, you can find green, unroasted coffee beans. Their "non-caffeine" aroma is capable of telling a lot of new things - someone describes it as a grassy one, it reminds someone of strong-brewed green tea, but someone thinks it smells of raw beans.
Imagine odorless coffee. What remains? Sour-bitter, astringent brown liquid. Where does this unique flavor come from, which is the essence of this drink, and what does it depend on?
An attractive and appetizing "signature" coffee aroma is acquired due to the volatile compounds that are formed during the roasting process. They arise due to the Maillard reaction - a chemical reaction between sugars and amino acids that occurs when heated and leads to a whole set of interconnected chemical transformations. The final taste and aroma depends on the composition and ratio of substances accumulated as a result of it. By the way, this same reaction is responsible for the formation of such compounds when frying meat or baking bread.
To the presence of different components in the air surrounding us, we are sensitive to varying degrees. Each odorous substance has a threshold for the perception of smell, that is, the minimum concentration that causes olfactory sensations. In the process of evolution, our sense of smell developed in such a way as to easily identify life-threatening compounds. It is not surprising that the human nose is very sensitive to putrescine and cadaverin, which determines the smell of rotten meat, and highly toxic hydrogen sulphide (the smell of rotten eggs) our olfactory organs catch already at a concentration of 0.000012 mg / l , despite the fact that fatal poisoning can only be obtained with 1.0 mg / l . However, we can feel some harmless smells familiar to us only when the surrounding air is already very saturated with them.
Each of the aromas of individual substances can be given its own characteristic: fruity, floral, earthy, coniferous, spicy and so on. But the characteristic smell of food products will be determined by their complex mixture, consisting of several tens or hundreds of such flavors.
About 800 substances are involved in the formation of a coffee smell. All of them are perceived by the olfactory receptors in different concentrations and with different intensities, and despite the fact that there are about 20 main components in this mixture, the characteristic aroma is ultimately obtained only due to the presence of seemingly insignificant components. To determine these substances in coffee, the method of gas chromatography was used (for more information on chromatography see Science and Life, No. 2, 1998 ), it turned out that in this set of compounds only a few in their pure form are recognized as “smelling coffee”. For example, pure furaneol found there also has a milky-caramel aroma, diacetyl has the aroma of butter, damascenon has roses and prunes, and 2-methylfuran, carbon disulfide, propionic and acetic aldehydes smell like fruits.
3-mercapto-3-methylbutyl formate , 3-methylbutanal and methylpropanal , defined as smells of burnt or fried, give more specific shades, defined as smoky smoked aroma, and 2-ethyl-3,5-dimethylpyrazine - a nutty woody note.
However, coffee aroma also contains components that have not very pleasant smells: seaweed (dimethyl sulfide), the musty, earthy smell of compost (2-methylisobornoleol), the smell of rotten cabbage (methyl mercaptan) and gasoline (thiophene), as well as many others characterized as unpleasant, harsh and even asphyxiating. But, despite the seeming unacceptability, without them the aroma of coffee would not be so full, so multifaceted and interesting.
It should be noted that the chemical composition of different types of coffee differs due to the different concentration of the main components. The final aroma will also be affected by the roasting time, its temperature, and the way to further store the beans, since most of the substances responsible for a specific coffee aroma are very unstable and are lost due to evaporation or interaction with other compounds.
Therefore, to feel the diversity of coffee aroma, try to drink fresh, just ground and just brewed coffee, and do not miss the opportunity to treat yourself to different varieties. After all, the more and the closer we get to know different flavors, the stronger we perceive and the better we will know them in the future.