How Tea Is Oxidized [Guide]

Have you ever wondered what goes into making a cup of tea? Going beyond the preparation of the leaves, many people overlook a very important step in the process, oxidation.

Oxidation is an essential component of tea production; it is the act of allowing tea leaves to come into contact with oxygen, which causes them to oxidize. This process not only affects the flavor and color of teas but can also change some of their health benefits as well. Unlike other drinks like wine and beer that have long-established oxidation processes, there are many different methods on how to oxidize tea.

In this article, we will explore how tea is oxidized as well as look at how oxidation changes depending on the variety or method used. We will examine oxidation's effect on different types of tea leaves and their flavors and aromas as well as potential health benefits that can be gained from properly oxidized teas.

How to oxidize tea

Have you ever left a half-eaten apple on the counter, only to return to discover that certain parts of the apple have darkened? This is oxidation!

In the context of tea, oxidation is a chemical process where tea leaves are exposed to air. During this process, the leaves dry and darken, affecting their strength, aroma, and flavor.

Oxidation begins the moment the tea leaves are plucked from the plant, and they are exposed to air. If the manufacturer intends to oxidize the tea leaves further, they may choose a variety of processes: Maceration, Rolling, or Tumbling.


Maceration is a process whereby the leaves are torn or bruised, to promote and quicken the oxidation process. This process is often used to make broken-leaf teas! This is the quickest process to achieve oxidation: through maceration, the insides of the tea leaves are immediately exposed to oxygen, hence the chemical process is quickened and full oxidation is quickly achieved.


Rolling is a slower and gentler oxidation process compared to maceration. The leaves are often rolled by hand or by a rolling pin, allowing them to oxidize.


In an even gentler process of oxidation, tea leaves are tumbled in large cylinders, or the leaves are hand-shaken in a shallow bamboo basket.

Halting Process

Regardless of the process of oxidation selected, when the leaves have been oxidized to the required extent, the process is halted by heating. For this, the leaves must be heated to about 150 degrees Fahrenheit. The common types of the halting process include:

  • Pan firing

Leaves are heated in a wok/pan, which is heated by gas or wood fire

  • Steaming

The tea leaves are steamed using a large vat of boiling water

  • Tumblers

A heated tumbler is used to heat the leaves

  • Baking

When an oven or similar machine is used to heat the leaves

After which, the process of tea oxidation is complete! Now, whenever you take a relaxing sip of your favorite tea, remember the hard work and processes that have occurred for this comforting cup of caffeine to be in your hands.

Types of tea by oxidation

Generally, tea is split into 4 categories: non-oxidized tea, semi-oxidized tea, oxidized tea, and fermented tea. Oxidation starts the moment that leaves are plucked from their plants, and the process of oxidation stops when the leaves are heated in factories. Hence, the categorization of tea into their separate categories would depend on the duration for which the tea leaves are allowed to oxidize, and when they are heated such that the oxidation process halts. We shall illustrate the different types of leaves in the table below!

Categories of tea / Level of Oxidation

The process to be done

Examples of Japanese tea

non-oxidized tea

Tea leaves are heated as soon as possible, such that the oxidation process is as short as it can be.

Japanese green tea (and Chinese green tea too!)

semi-oxidized tea

Tea leaves are allowed to oxidize for a period of time, and the leaves are heated at an ideal timing such that partial oxidation is achieved.

This ideal timing is determined by manufacturers, and different producers will have different durations depending on their preferences!

Oolong tea

oxidized tea

Tea leaves are only heated when they are fully oxidized.

Black tea

fermented tea

While these types of tea are first sorted into the 3 categories above, they are later fermented by microorganisms after heating.

Goishicha or black stone tea (from Kochi, Japan!)

Green tea originated in China, which makes sense seeing as the country's rich culture has a deep appreciation for teas of all kinds. Yet, when traveling to Japan, one might find that Japanese green teas have become more popular than their Chinese counterparts.

It is undeniable that each country produces amazing quality green teas with unique flavor profiles and health benefits. To help you navigate through the sea of options out there, let’s take a look at the differences between Japanese green tea and Chinese green tea so you can make an informed decision about which is best for you!

Kyoto is known for its traditional Japanese culture and unique blend of old and new. Also popular among food lovers, Kyoto is known for its delectable matcha treats.


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