Fermented tea drinks like kombucha have become quite common in the West, so it’s easy to assume that other tea types, like green tea, can be fermented too. However, this is actually a common misconception.
Although the term “fermentation” is often used when describing green tea processing, green tea is not actually fermented, but oxidized. Fermentation refers to the breaking down of organic material by bacteria or fungus, which does not happen during green tea processing.
Oxidation is a process through which tea leaves are exposed to the air in order to dry and darken, which changes the flavor, aroma, and strength of the tea.
As we hinted above, what does happen during green tea processing is oxidizing, which occurs when oxygen reacts to enzymes within the tea leaves’ cell walls. Still confused?
Let’s break down where this misconception of green tea fermentation began, as well as the individual processes used to make both green and fermented tea.
Fermentation vs. Oxidation in Tea
There are two main reasons for the confusion between fermentation and oxidation in the tea world:
- Tea was invented thousands of years before the scientific understanding of the two processes and their differences.
- Tea was invented in China, so much of what we know about it in the West has been translated; this always opens the door to potential misunderstandings.
Tea Making is an Ancient Art Form
When talking about tea, we must keep in mind that the process used today is much the same as it was thousands of years ago.
To people without the benefit of science, oxidation and fermentation would likely have seemed much the same, and it’s no wonder why they’d use the terms interchangeably. Once we understood the difference between the two, the words had already embedded themselves into the tea making vernacular.
Some Words Get Lost in Translation
China is known as being the birthplace of tea, and until relatively recently, all tea consumed was imported from Asia. This means that much of what we in the West about the tea process was translated from Chinese and other Asian languages, and the translation is never perfect.
It’s easy to imagine how two similar concepts like fermentation and oxidation could be interposed in translation, and since many people, even today, don’t quite know the difference, the inaccurate descriptions continue.
It doesn’t help that what we call “black” tea, the Chinese call “red” or “dark” tea, adds to the confusion. “Black” and sometimes “dark” tea is usually referring to post-fermented tea like hei cha or pu-erh.
How is Green Tea Made?
Many people are surprised to learn that most of the teas we’re familiar with are from the same plant (Camellia Sinensis), and processed in almost the same way.
The only difference in the processing of different teas is how much the tea leaves are allowed to oxidize. This one step drastically changes the color, strength, and flavor of the tea.
- White: Oxidized barely at all
- Green: Oxidized a little (less than 30%)
- Black: Oxidized a lot (more than 70 or 80%)
- Oolong: Oxidized anywhere from 30-70%
For example, as you can see from the above list, green tea is oxidized far less than black tea, making it a lighter and more mellow tea with “grassy” flavor notes.
Steps to Processing Green Tea
To understand how important this one step (oxidation) is, it might help to understand what tea processing looks like.
Tea plants are usually grown in tropical and subtropical climates where the weather is warm, and the air is humid. It’s very common for tea plantations to be situated on hillsides, foothills, and mountains. The higher altitude often provides greater humidity, which is vital to the health of tea plants.
Tea plantations can be small, single-family businesses, or more extensive operations run by large corporations.
Harvesting is usually done twice a year and can be done by hand, machine, or a combination of both.
Higher quality teas and teas, which are less oxidized, are more likely to be selected by hand. Lower quality teas and black tea can be picked by machine since it won’t matter if the leaves are accidentally damaged during harvesting.
As soon as leaves are plucked, they’re laid out in the sun or an airy room to wilt or wither, losing much of their water content; this usually takes a few hours.
Note: White teas will usually skip the next two steps and go right to the “fixing” stage. Green teas will often skip the “bruising step” but still be allowed to oxidize a bit (though not as much as black teas).
Bruising, also called leaf disturbance and leaf maceration, is exactly what it sounds like. After the wilting stage, leaves are:
This can be done by hand or machine. The purpose of damaging the leaves is to allow more of the leaves’ cell walls to come into contact with air, so they’ll oxidize faster and more thoroughly.
If you picture cutting an avocado in half versus smashing it up for guacamole, it’s the same principle. The half avocado will only brown on the surface, leaving the inside green and fresh. The mashed one will begin to brown throughout pretty quickly.
Black tea is pretty much always rolled or otherwise damaged, and it’s not uncommon for oolong, depending on the desired oxidation level.
Oxidation technically starts the moment the tea leaf is plucked and only stops once heat is added (in the next step). This is arguably the most crucial step of the tea making process, as it will have the most significant effect on flavor, and ultimately, the type of tea that comes out of the final product.
As we mentioned, some teas are more oxidized than others, resulting in different flavor profiles:
- Less oxidized: delicate, mellow, grassy, floral
- More oxidized: rich, malty, full, earthy
The oxidation step is like the wilting step, in that the leaves are set out in the sun or an airy room. They’ll start to darken as they oxidize.
Once the tea leaves have oxidized to the desired level, they’re “fixed” using heat, to deactivate the enzymes and stop the oxidation process.
This can be done in several ways. The most used are:
- Roasting in a wok
Once the oxidation has been stopped, the leaves are laid out one last time to dry, usually in the sun. This preserves their taste and gets them ready for sale.
How Are Fermented Teas Made?
There are several fermented teas, most of which aren’t super popular in the West:
- Hei Cha
- Pickled Tea Leaves
Each fermented tea is made differently.
Hei Cha and “Ripe” Pu-Erh
Hei cha and ripe pu-erh are true fermented teas, often called post-fermented. They both go through the traditional tea process (including oxidation) and are then stored in piles where they’re kept warm, wet, and covered in cloth for several weeks. This allows bacteria and fungus to grow, effectively fermenting the tea.
Kombucha is a tea drink that’s gained popularity in the West for its potential health benefits. It’s made by adding sugar, yeast, and bacteria to tea and letting it ferment. This results in a slightly carbonated, slightly alcoholic drink said to be excellent for digestion.
Pickled Tea Leaves
Fermented or pickled tea leaves are popular snacks in many Asian countries, a treat that hasn’t quite reached the West yet.
It’s easy to understand why people are confused when talking about tea oxidation versus fermentation, but as you can see, they are two separate processes that result in very different finished products.
All teas go through oxidation during processing, but only certain teas go through a fermentation process. Green tea is not fermented, but it is oxidized, and it’s delicious!