1. Black Tea Is Made from the Same Leaves as Green Tea in 4 Steps
The standard method for making black tea, known as the orthodox method, involves four stages: withering (making the leaves wilt), rolling, oxidation, and drying [2]. Unlike green tea, which uses heat at the beginning to stop the enzymes, black tea does not use heat until the final stage. The order of using heat is reversed [1].
In this context, "fermentation" does not refer to the action of microorganisms like those in natto or yogurt. It refers to oxidation caused by oxidizing enzymes within the leaves [1]. Some English sources note that this term is not entirely accurate [5].
2. Withering: How Leaves Lose Water and Build Up Aroma
Freshly picked leaves contain about 70–80% water by weight. During withering, this is reduced to about 60–70% [2]. While the ideal time varies by study, some suggest 14–18 hours [2].
What happens during this time is not just a loss of water. The components in the leaves break down, increasing the substances that become the basis for aroma, as well as sugars and amino acids [2]. Temperature also affects the result. One study reports that withering at a lower temperature, such as 22°C, tends to produce black tea with a brighter color [2].
3. Rolling: How Breaking the Leaf Cells Mixes Enzymes and Catechins
The withered leaves are rolled strongly by machine or by hand. This is called rolling. Rolling breaks the cell structure, allowing catechins and oxidizing enzymes to meet. It also increases the surface area of the leaves that is exposed to air [2].
Most of the theaflavin, which is the basis for the red color of black tea, is formed during this rolling stage [2]. One study found that when the rolling temperature was kept at about 20°C, the enzymes worked well, theaflavin increased, and the color became brighter [2].
A cut apple turns brown because polyphenols at the cut surface are oxidized. The more cells are broken, such as when grated, the stronger the discoloration becomes [4]. However, because the components in apples and tea leaves are different, the pigments produced are not the same.
4. Oxidation: How Leaves Change from Green to Copper-Brown
The rolled leaves are spread out in a place where temperature and humidity are controlled. During this time, enzymes continuously oxidize catechins, turning them into two types of pigments: theaflavin and thearubigin [2]. If this process proceeds moderately, the leaves change from green to a copper-like brown [2].
Theaflavin is related to the bright color and sharp taste of black tea. Thearubigin is related to the richness of the flavor and the orange-brown color of the liquid [2]. Reports indicate that if the oxidation time is prolonged, thearubigin increases while theaflavin decreases [2].
Regarding large components like thearubigin, a commentary in a journal by the Japanese Society of Agricultural and Biological Chemistry states that while it is known that high-molecular-weight polyphenols in fermented tea are made from catechins, their chemical structures remained unknown for a long time [3]. There are still parts of the tea we drink every day that are not fully understood.
5. Drying: How Heat Stops the Enzymes and Sets Color and Aroma
Leaves that have undergone oxidation are dried with hot air. The heat stops the enzymes from working, which stops the oxidation [2]. In black tea, this heat is the final move that determines the color.
Drying also serves to reduce moisture so the tea can be stored. Furthermore, it is said that reactions that improve color and aroma proceed during the drying process [2].
Green tea stops enzymes at the beginning to keep the green color. Black tea stops them at the end to make the brown color. Where the enzymes are stopped creates the difference between these two teas.
6. Japanese Black Tea: Making Black Tea from Japanese Tea Leaves
Black tea made with Japanese tea leaves is called domestic black tea, *wa-kocha* (Japanese black tea), or *ji-kocha* (local black tea). Many are made on a small scale, with characteristics specific to each region. They often use leaves picked after the first flush of green tea, though tea trees bred specifically for black tea are also being cultivated in recent years [1].
There are two main methods for making black tea worldwide. The "orthodox method" rolls the leaves while keeping their shape. The "CTC method" crushes, tears, and curls the leaves. CTC is said to have been developed in 1930 and is used for fine tea leaves in tea bags [5]. A review reports that CTC black tea has more theaflavin and thearubigin, but fewer floral aroma components [2].
Tada Genkichi is a figure involved in Japanese black tea production. According to materials from Futtsu City, he was ordered by the government in 1875 to inspect China and India. In 1876, he traveled to Assam, Darjeeling, and Ceylon Island, returning in 1877. After returning, he taught tea processing in various places. The black tea trees brought back from Assam were cultivated in Maruko (Shizuoka City) [6].
7. How to Compare Green Tea and Black Tea Yourself
Prepare one green tea bag and one black tea bag, and compare the tea leaves inside. You can also pour the same weight of hot water into each and see how the darkness and brightness of the color differ. When using hot water, be careful of burns and do this with an adult [1].
If you find domestic black tea in a shop, look at the ingredients and origin on the back of the package. It may state which variety was used and whether it was made from leaves picked after the first flush [1].