The fragrance of tea depends on the essential oils and tar substances that are contained in plants. Essential oils are complex mixture of substances that belong to the most diverse class of compounds which are soluble in organic solvents and possessing the ability to escape from water vapor. Overall the total content of essential oil is minimal; it is determined by only hundredths of a percent. For example, aromatic black tea contains about 0.02% of oil. Pure essential oil of fresh tea leaf is a green color with a strong fragrance of fresh greens. In the technological processing of tea leaf occurs the formation of a new aromatic substances that contribute to the specific flavor of the finished product. Thus, the composition of essential oil of green plants is different from the finished black tea. The substances that make up the oils can be divided into 4 main classes of compounds: acids, carbonyl compounds, alcohols and phenols. These volatile compounds found in tea are trace amounts - 0.01% of dry matter, but their role in the establishment of the tea flavor is tremendous.
Some parts of the plant contain different amounts of volatile compounds, which, in turn, differ in their compositions. The maximum concentration of essential oil found in the tender stems and leaves. The top leaf with the growing bud and two next leaves are equivalent to the content of essential oil. Further down the stem, as general coarsening occurs, oil content decreases. Which explains why the top three leaves are the most vaulable for high quality tea.
In the formation of the aroma of tea, the main role is played by aromatic aldehydes (Organic compound that has OH-group in its structure. They are used in organic synthesis as fragrances). In the composition of essential tea oils are vanilla, lavender, cinnamon aldehydes, etc. During the processing of tea leaves into black tea, the various fractions of volatile compounds undergo significant changes. The total content of these compounds increases most radically in the early stages of rolling. In the process of withering the relative content of components with higher boiling point reduces and low-boiling point, on the contrary, increases.
Along with essential oils important role in creating a tea aroma played by various resinous substances - carriers of flavor. They are in a close chemical relation with essential oils and are a complex mixture of different classes of organic compounds.
The content of tarry substances in tea leaves ranges on average from 3% to 6%. These substances are separated by several fractions, the most valuable of which is a neutral faction. It has a pleasant sweet floral aroma. In the process of technological treatment , the amount of this fraction in tea leaves increases by 40%.
During the processing of tea leaves, the content of resinous substances decreases, indicating the result of oxidation. I.e. ratio: fresh leaves – 3.48%, withered leaves – 3.27%, after two hours of curling – 2.92%, semi-finished product – 2.35%.
Through fragrance of tea, all the deficiencies that have arisen as a result of violations of technological regimens or improper storage of products, can easily be found. Disadvantages may include: acidity, mustiness, smell of the green, smoke and other uncharacteristic for tea scents. Most difficult to improve defect is acidity, which results in a violation of the fermentation process. Since in the processing of tea leaves, especially during the fermentation, occurs a reduction of Tannin. Therefore, the tea produced in violation of this process turns out with a bitter flavor and pale color of infusion. The cause of the smell of greenery is an infringement of withering, rolling, and fermentation. Such a tea has a mild flavor that the brew is a greenish color in the cup with a greenish ring on the surface and instead of the characteristic astringent taste; this product has a bitter taste. If there is excessive moisture in semi-finished product (more than 7.5%) tea is aging much faster. For extended storage. it gets the smell of dampness and can come in unsuitable conditions for consumption.
In addition, it is worth noting that different varieties of tea, as well as different ways of brewing, have an imprint on the final quality of the drink