What smells like coffee?
Coffee is 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, the grains obtained from the fruits of these trees: Coffea arabica L. - Arabica and Coffea canephora Pierre ex Froehn., Or robusta, sometimes called Congolese coffee. On these two types, according to various estimates, up to 98% of coffee produced. This volume is divided in a ratio of 70% - arabica, 30% - robusta. The other types of coffee account for only 2% of world production. The most common grade of coffee, arabica, grows at an altitude of 900 to 2000 meters above sea level. Grains, as a rule, have an oblong shape, a smooth surface, a slightly curved in the shape of the letter "S" line, in which usually after uncombusted 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 the tropical regions of Africa, India and Indonesia. Grains have a rounded shape, color - from light brown to grayish-green. Robusta is usually considered less refined than coffee in terms of flavor. At the same time, it contains more caffeine, and is also often used in espresso mixtures, which allows you to achieve better quality coffee foam and cheaper mix.
In specialized stores you can find green, unroasted coffee beans. Their "non-coffee" flavor is able to tell a lot about the new - someone describes it as herbaceous, to someone it resembles a brewed green tea, and to someone it seems that it smells of raw beans.
Imagine coffee without a smell. What is left? Acid-bitter, astringent brown liquid. Where does this unique aroma that makes up the whole essence of this drink come from, and what does it depend on?
Attractive and mouth-watering "branded" coffee aroma is acquired due to volatile compounds that are formed during roasting. They are due to the Mayar reaction - the chemical reaction between sugars and amino acids, which occurs when heated and leads to a whole set of interrelated chemical transformations. The final taste and aroma arises depending on the composition and the proportion of substances accumulated in its result. 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 surrounding air, we are sensitive to varying degrees. Each odorous substance has a threshold of perception of the smell, that is, the minimum concentration that causes the olfactory sensations. In the process of evolution, our sense of smell developed in such a way that it is easy to identify dangerous compounds for life. It is not surprising that the human nose is very sensitive to putrescine and cadaverine, which determines the smell of rotten meat, and highly toxic hydrogen sulphide (the smell of rotten eggs), our sense of smell is already detected at a concentration of 0.000012 mg / l , while deadly poisoning can only be obtained if 1.0 mg / l . However, we can only feel some sort of harmless odors when the surrounding air is already saturated with them.
Each of the flavors of individual substances can be given its own characteristic: fruit, floral, earthy, coniferous, spicy and so on. But the characteristic smell of food 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 coffee odor. All of them are perceived by olfactory receptors in different concentrations and at different intensities, and, despite the fact that the main constituents in this mixture of odors are about 20, the characteristic aroma ultimately results only from the presence of seemingly insignificant components. To determine these substances in the coffee, the method of gas chromatography was used (for more details on chromatography, see Science and Life, No. 2, 1998 ). It turned out that in this set of compounds only a few in pure form are recognized precisely as "smelling coffee". For example, the furaneole found in the same place has a milky caramel flavor, diacetyl is a flavor of butter, damascene is a rose and prune, and 2-methylfuran, carbon disulphide, propionic and acetic aldehydes smell of fruit.
More specific shades attach to 3-mercapto-3-methylbutyl formate , 3-methylbutanal and methylpropanal , which are defined as smells of burnt or roasted, guaiacol gives a smoky smell of smoking, and 2-ethyl-3,5-dimethylpyrazine is a nutty woody note.
However, there are components in the coffee aroma that have not very pleasant smells: seaweed (dimethyl sulfide), musty, earthy smell of compost (2-methylisoborneol), smell of rotten cabbage (methyl mercaptan) and gasoline (thiophene), and many others , Characterized as unpleasant, harsh and even suffocating. But, despite the seeming unacceptability, without them the aroma of coffee would not be so complete, so multifaceted and interesting.
It is worth noting that the chemical composition of different varieties of coffee differs due to the different concentration of the main components. The final flavor will also be affected by the roasting time, and its temperature, and the way the grains are stored further, since most of the substances responsible for the specific coffee aroma are very unstable and lost due to evaporation or interaction with other compounds.
Therefore, to feel all the variety of coffee aroma, try to drink fresh coffee, freshly ground and just cooked, and do not miss opportunities to treat yourself with different grades. After all, the more and the closer we get to know the different flavors, the more we perceive and the better we learn them in the future.