Did you know that green tea, black tea, oolong tea, and other teas we usually drink, which differ in taste, aroma, and color, are all made from the same tea leaves?

In this article, we will explain the manufacturing process and characteristics of oxidized tea (black tea), including why it is called fermented tea and how the aroma is produced. 

Characteristics of manufacturing process of oxidized tea (black tea)

Black tea is made through complete enzymatic fermentation, which is why it is often referred to as fermented tea. Unlike unoxidized teas such as sencha and deep steamed sencha, fermented tea is oxidized and fermented using the oxidizing enzymes in the tea leaves. Initially, it was an "ingenious process (handmade process)" that originated in China about 200 years ago, but nowadays, it is often made by machine.

There are two main production methods: "orthodox" and "unorthodox," and a combination of the two has also been produced. Here we will introduce the traditional "orthodox" method.

Fermentation or oxidation?

Fermentation, in the world of tea, refers to Fermentation, in the world of tea, refers to oxidation caused by oxidizing enzymes in tea leaves, rather than fermentation caused by microorganisms such as miso or yogurt.

Oxidation is a process in which oxygen and enzymes combine to alter the original ingredients.

While some teas are fermented by microorganisms, such as post-fermented teas, the tea industry refers to this oxidative process as fermentation.

From plucking fresh leaves to shipping

Tea leaves are grown in tea plantations. The leaves picked during the harvest season are transformed into Aracha (crude tea) after being kneaded and dried. The tea is then finished and becomes a product ready to be shipped.

How to make Aracha : A Guide to Processing Fresh Tea Leaves

Aracha is a type of Japanese green tea that undergoes a unique processing method. To make it, fresh tea leaves are plucked and then subjected to a series of processes including withering, rolling, ball breaking/sieving, oxidation, and drying. Once the tea leaves go through these processes in the correct order, they become Aracha. After the finishing process, the tea is then shipped across the country.

1. Withering

The first step in making Aracha is withering. This process involves wilting the fresh leaves to remove the water content evenly. In the past, the leaves were often dried in the shade, but nowadays, "artificial wilting" is used. In artificial wilting, the leaves are wilted in a wilting tank with a large amount of warm air.

2. Rolling

Tea leaves are processed by breaking down and shaping their cells using oxidizing enzymes. Upon exposure to air, these enzymes are activated, and oxidative fermentation occurs in catechins, pectin, and chlorophyll, resulting in the distinct taste, aroma, richness, and color of black tea.

The fermentation process takes 45 to 90 minutes but can be slowed down by using a ball breaker. The tea is then cooled and rubbed repeatedly to suppress the fermentation process. These steps are crucial in determining the differences between black and green tea. 

3. Ball breaking/sieving


Ball breaking and sieving are crucial steps in the tea production process. During the rubbing process, tea leaves tend to clump together, and they need to be unraveled to promote oxidative fermentation. To achieve this, tea leaves are run through a ball unraveling machine every 20 to 30 minutes.

Afterward, the tea leaves are sieved through a mesh, and the smaller leaves that pass through the mesh are transferred to the next process. These leaves are called "under the sieve." The larger leaves that remain on the sieve are called the "top of the sieve." These leaves are returned to the twisting process. By following these steps, tea producers can produce high-quality tea that has an excellent taste and aroma.

4. Oxidation(Fermentation)

In a fermentation chamber, tea leaves are spread evenly to a thickness of 4-5 cm and left to ferment for 2 to 3 hours at a temperature of 25-26°C and 90% humidity.

This process turns the green leaves into a bright reddish-bronze color and fills the air with a tea-like aroma. However, over-fermentation can spoil the tea's original aroma and turn its watercolor black. Thus, it is crucial to determine the right time to stop the fermentation process.

5. Drying

Drying tea leaves is an essential step at the end of the fermentation process. Leaving the leaves with high water content can lead to continued fermentation. To prevent this, the leaves are dried with hot air at approximately 100 degrees Celsius. This process inactivates oxidative enzymes and reduces moisture to less than 5%. Properly dried tea leaves will ensure a consistent and high-quality tea product.


The tea undergoes a finishing phase after drying, which involves sorting, shaping, and blending in that order to be ready for shipment. This final process is crucial in transforming the tea from "Aracha" to a market-ready product.

6. Sorting (Grading)

Aracha, the raw tea leaves, goes through a sifter multiple times to ensure they are sorted by size and shape. This process classifies the tea leaves into different grades, which is known as "leaf grade."

7. Blending

The final step in tea production is blending the leaves. The process involves selecting over 20 types of tea leaves from the same production area to stabilize the quality. It's not about mixing various kinds of tea leaves but rather ensuring that the tea blend is of high quality and meets consumer tastes.

Blending influences the price of each black tea. The key is to suit consumer tastes by blending the right types of tea leaves. By doing this, tea makers can produce high-quality tea blends that are loved by consumers.

January 08, 2023