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Are you curious about the ingredients in your oolong tea? Knowing the ingredients can help you understand the effects you can get from oolong teas.

Oolong tea Ingredients

Oolong tea is created by fermentation, which means its ingredients are similar to black tea. The most unique characteristics of black tea ingredients are catechins and aroma components.


Catechin is a polyphenol, also called tannin. It is a typical ingredient of tea, and the astringency taste comes from catechin. However, in the case of oolong tea, catechin is turned into theaflavin and tearbidine through oxidation.

Theaflavin / Thearbigin

Tea lovers, did you know that the beautiful brown color of oolong tea is due to theaflavin and thearbigin? These substances are formed through the oxidation of catechin, an ingredient that doesn't have any color on its own. Theaflavin has an orange color, while thearbigin is red, which is why the color of tea leaves changes from green to dark brown.

While oolong tea has less oxidation compared to black tea, it still contains theaflavin and thearbigin, although the amounts are smaller. This means that the color of oolong tea is different from black tea.


Caffeine is a natural compound found in tea leaves, and it is responsible for the bitter taste of tea. Interestingly, the processing of oolong tea leaves does not affect the caffeine content, which remains the same before and after processing.

In fact, tea leaves contain about 3% caffeine by weight, which is 2-3 times more than the same amount of coffee beans. However, the amount of caffeine in a cup of tea is much lower than that in a cup of coffee due to the difference in the amount of tea leaves and coffee beans used per cup. Moreover, caffeine is easier to extract from crushed coffee beans than tea leaves.

To extract caffeine from tea, hot water with a temperature higher than 80℃ is needed, as caffeine does not dissolve in water below 50-60℃. Oolong tea is typically brewed with 95℃ water, which results in a higher caffeine content compared to green tea.


Saponin is an ingredient that contributes to the bitterness of tea, although in small amounts. It acts as a surfactant, causing the tea to foam. Although the amount is too small to expect any significant health benefits, it is an essential component of the tea's bitter taste.

Amino acid

Amino acids are essential ingredients that contribute to the umami taste of tea. Some of the most common amino acids found in tea include theanine, glutamic acid, aspartic acid, arginine, and serine. Theanine, in particular, accounts for about 50% of the total amino acid content in tea and is a typical ingredient in most varieties.

Unlike other compounds, amino acids do not change through oxidation, which means that they are present in oolong tea leaves. However, since oolong tea is cultivated without a covering process and the use of nitrogen fertilizer, the final amount of amino acid in the leaves is relatively smaller compared to green teas.

Furthermore, caffeine and catechin are extracted largely with high temperatures, resulting in bitterness and astringency that can overpower the umami taste of amino acids. As oolong teas are usually brewed at high temperatures, the taste of amino acids is rarely prominent.

Aroma component

Tea leaves contain a few aroma components before processing. However, during the crumpling process of tea leaves, the cell walls are destroyed, and oxidation is intensified. This leads to the formation of flower-like or fruit-like aroma components.

Green tea has fewer aroma components since it doesn't undergo oxidation. Black tea and oolong tea, on the other hand, contain more than 600 and 200 types of components, respectively. As fermentation progresses, more aroma components are created. Thus, black tea has more aroma components than oolong tea.

The main aroma components in oolong tea are Linalool (lemon-like scent), Geraniol & Indole (flower-like scent), Nerolidol (jasmine-like scent), and Jasmine lactone (peach and apricot-like scent).

[Tadakatsu Takeo(1983), Variations in the Aroma Compound Content of Semi-Fermented and Black Tea]


Fresh tea leaves are rich in vitamins A, C, E, B, among others. However, during the processing of tea leaves, these vitamins are oxidized and converted into other compounds. As a result, oolong tea leaves contain almost no vitamins.


Chlorophyll is a green pigment found in fresh tea leaves. Unfortunately, during the processing of tea leaves, the chlorophyll gets oxidized and transformed into other ingredients. As a result, oolong tea leaves contain almost no chlorophyll.

Many ingredients are contained in black tea leaves

Black tea leaves contain numerous ingredients that contribute to their distinct taste, aroma, and color. The specific types and quantities of these ingredients vary depending on the processing methods used, resulting in the unique characteristics of each type of oolong tea.