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?

These teas have different tastes and aromas due to the differences in their production methods.

In this article, we will explain why black tea is called fermented tea and how the aroma of black tea is produced, along with the manufacturing process.

Characteristics of manufacturing process of oxidized tea (black tea)

The fermented tea is tea made through complete enzymatic fermentation.

Contrary to 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," A combination of the two has also been produced.

Here we introduce the traditional "orthodox" method.

Fermentation or oxidation?

Fermentation, as used in the tea world, refers to oxidation caused by oxidizing enzymes in tea leaves, as opposed to fermentation caused by microorganisms (bacteria) such as miso or yogurt.

Oxidation is a reaction in which oxygen and enzymes combine to change the original ingredients.

Microorganisms, such as post-fermented teas, ferment some teas, but the tea industry refers to this oxidative fermentation as fermentation.

From plucking fresh leaves to shipping them

Tea leaves are grown in a tea plantation. The tea leaves plucked in the picking season become Aracha (crude tea) after kneading and drying. Then, through “finishing,” the tea becomes a product to be shipped.

How to make Aracha

The plucked fresh leaves undergo the processes of withering, rolling, ball breaking/sieving, oxidation, and drying in this order to become Aracha. Then, after the finishing process, the tea is shipped across the country.

1. Withering

Wilting the fresh leaves to remove the water content evenly is called wilting.

In the past, the leaves were often dried in the shade, but nowadays, "artificial wilting," in which wilting is carried out in a wilting tank with a large amount of warm air, is used.

2. Rolling

The cells of the tea leaves are broken down and shaped by the oxidizing enzymes in the leaves.

When the oxidizing enzymes are exposed to oxygen in the air, they are activated, and catechins, pectin, and chlorophyll undergo oxidative fermentation. These oxidative enzymes are the key elements that create black tea's aroma, taste, richness, and watercolor and lead to the differences between black and green tea.

The tea is fermented for 45 to 90 minutes. Still, to prevent the oxidative fermentation from advancing too quickly, the tea is put through a ball breaker to suppress the fermentation process, cooled, and then repeatedly rubbed again.

3. Ball breaking/sieving

Since the tea leaves clump together during the rubbing process, they are unraveled to allow for average exposure to air, which further promotes oxidative fermentation. The tea leaves are put through a ball unraveling machine during this process every 20 to 30 minutes.

The tea leaves are sieved through a mesh, and those sieved down are called "under the sieve" and transferred to the following process. The larger leaves on the sieve are called the "top of the sieve" and are returned to the twisting process.

4. Oxidation(Fermentation)

In a fermentation chamber with room temperature set at 25-26°C and humidity at 90%, tea leaves are spread evenly to a thickness of 4-5 cm and left to ferment for 2 to 3 hours. During this process, the green leaves turn a bright reddish-bronze color, and a tea-like aroma waft through the air.

However, if the tea leaves ferment too much, the original aroma of the tea will be spoiled, and the watercolor will turn black. Hence, it is necessary to determine when to stop the fermentation process.

5. Drying

Tea leaves at the end of fermentation still have a high water content, and if they are left as they are, fermentation will continue, so they are placed in a dryer and dried with hot air at a temperature of around 100 degrees Celsius. Drying inactivates oxidative enzymes and reduces moisture to less than 5%.


The tea after drying is already called “Aracha,” but it cannot be shipped as a product yet. In the finishing phase, it undergoes sorting/shaping and blending in this order to be ready to ship as a product.

6. Sorting (Grading)

Aracha goes through a sifter several times to be sorted by the size and shape. Sorting classifies the tea leaves into grades. This grade is called “leaf grade.”

7. Blending

The final step is blending the leaves. Over 20 types of tea leaves are used, but the purpose is not to mix various kinds. It is to stabilize the quality by choosing teas from the same production area. Blending influences the price of each black tea, and what matters is how to suit consumer tastes by blending.

January 08, 2023