Taiwan’s Oolong Tea processing methods are renowned for being some of the best in the world. The island produces over ten varieties of Oolong Tea, each with its distinct characteristic and flavor. There are a lot of steps in making Oolong Tea and each affects the taste of the final brew. Here, we provide an an answer to the question, how is Oolong Tea processed?
Tea Manufacturing Process Flow Chart
All in the Processing
Oolong Tea traditionally comes from southern China and Taiwan, and like most teas, is made from leaves of the Camellia sinensis plant. Like other teas, the unique flavor of Oolong Teas come from the way they are processed. The oxidation level of Oolong Teas varies from 8-85%, which is between Green Tea (0% oxidation) and Black Tea (100% oxidation). This degree of oxidation, and the many ways of processing it, give Oolong Tea its broad spectrum of flavor and character. Flavors range from floral and green to sweet and fruity, and on to woody and smoky. In Taiwan alone, there are over ten different types of Oolong Teas.
Taiwanese Oolong Teas have a variety of flavors due to the different levels of oxidation and roasting
Cultivating Tea Leaves
Taiwan, though geographically small, has perhaps the largest variety of Oolong Tea types per area, due to its variation in geography, climate, and cultural history. From Tie Guan Yin, produced in the low-lying hills southeast of Taipei, to the High Mountain Tea growing regions of central Taiwan, there are dozens of tea types produced on this small island off the southeast coast of mainland China.
A tea farm in Taiwan
Tea plants are grown in rows on tea farms ranging in size from less than a hectare to hundreds of hectares. Tea cultivation in Taiwan has a rich history of migration from mainland China, as well as influences from the Portuguese and Japanese. Today, there is a mix of small-scale private farms throughout the island, with high volume production in central Taiwan. Many small-scale independent farmers use organic or other methods of sustainable farming. All of Eco-Cha’s tea sources use relatively sustainable methods with some being organically certified.
Harvesting Tea Leaves
Timing
Tea leaves for Oolong Tea production in Taiwan are typically harvested three to four times a year. Although at lower elevations, it’s possible to harvest year-round, for up to six harvests annually. Spring harvest is usually the best in terms of quantity as well as quality. Winter harvest is often minimal, although it can also be quite good quality. Fall harvest can also offer fine produce, and summer tea is either processed as Black Tea, or not harvested at all — allowing the tea trees to replenish.
New tea leaf growth ready for harvest
Hand Harvesting
The top three to four leaves of new growth (within 60 days) from a tea plant provide the ideal raw material for making Oolong Tea. Picking tea by hand is the best way to harvest this new growth, but this is very labor intensive. The majority of tea pickers in central Taiwan are now migrant workers from Vietnam or other southeast Asian countries. The younger generation in Taiwan has mostly left the farm for more modern livelihoods.
Harvesting tea leaves by hand in Taiwan to make into Oolong Tea
Watch how tea leaves are harvested by hand and carried from the fields in the video below.
Machine Harvesting
Consequently, machine harvesting tea leaves is becoming increasingly common. These tea harvesting machines are essentially a hedge trimmer with a vacuum machine and bag attached to catch the trimmed leaves. With proper farm management, the compromise in the quality of harvested leaves is becoming less and less significant. And farmers are realizing that proper farm management, combined with skillful and painstaking processing methods, can produce high quality tea from machine harvested leaves.
Once tea leaves are harvested, transformations on the cellular level that affect the taste of tea begin, so tea makers must start processing the tea as soon as possible, and continually tend to the leaves until the final product is made. This is particularly true of Oolong Tea processing.
Withering
After tea leaves are harvested, enzymes inside the leaves immediately start chemical reactions that create the flavor and aroma profile of the final tea. The leaves start to wilt and go limp at this stage as moisture is lost. The tea maker can control how far the reactions go by controlling how much moisture the tea leaves lose in a process is called withering. The tea maker must pay careful attention to the atmospheric conditions, and the state of the leaves to get the effect he/she wants. This is where the acquired skill of Oolong Tea making is most essential.
Solar withering of tea leaves in Taiwan
Leaves to make Taiwanese Oolong Teas are usually first spread outdoors to wither in the sun in a process called “solar withering”. The tea maker tosses and shifts the leaves to ensure even exposure, and stimulate circulation in the leaves, in order to induce uniform dehydration. After the initial solar withering, the leaves are moved indoors to continue withering. Traditional tea processing uses round woven bamboo trays that are stacked on racks. More modern processing facilities use much larger steel-framed trays that are mechanically positioned and stacked — providing much more surface area and uniform circulation of air.
Indoor withering or tea leaves on traditional bamboo trays
After about a third of the moisture is depleted, the leaves are then ready for the next stage of processing.
Oxidation
The process of oxidation causes more chemical reactions within the tea leaves, adding to the flavor profile of the tea. During this step, the cell walls of the tea leaves are broken to allow exposure to oxygen. In Taiwan, this is typically done by tumbling the leaves in long woven bamboo cylinders. The physical agitation breaks down the cell walls. With depleted moisture and exposure to air, the chemical reaction of oxidation occurs.
Tea leaves can be oxidized inside bamboo tumblers like this one
Oxidation, besides changing the flavor of the tea, also changes the color of the leaves to a darker hue. The more oxidation, the darker the color. That is why Black Teas (fully oxidized teas) are are a deep dark red color. Oxidation also plays a major role in the difference between Oolong Tea vs Green Tea. Oolong Teas, which have an oxidation of 8-85%, can range in color from green to a reddish hue. Here, the skill and experience of the tea maker again plays a very important role to control the level of oxidation for the desired type of tea.
Jin Xuan Oolong Tea (on left) is lightly oxidized and is lighter in color. Red Jade Black Tea (on right) is heavily oxidized and has a much darker hue.
Kill Green
After the desired level of oxidation is reached, oxidation is halted by high temperature tumble heating the leaves in a process called “Kill Green”, or “fixing”. The name “Kill Green” comes from the Chinese term 殺青 (shaqing), which literally translates as “kill green”. This step deactivates the enzymes responsible for the oxidation process, thereby stopping the chemical transformation.
Oolong Tea makers in Taiwan typically use heated tumble dryers for the kill green process, though pan frying by hand can also be used.
The "kill green" or fixing of tea leaves in heated tumblers
Oolong Rolling & Tea Drying Process
After the Kill Green process, leaves destined to become Oolong Tea are rolled and dried. During this phase, Oolong Tea leaves that undergo modern machine rolling take on a characteristic ball shape. Semi-rolled Oolong Tea leaves can be less tightly rolled into a “shrimp shaped” dried leaf form using more traditional labor intensive methods.
Rolling of Oolong Tea leaves in Taiwan usually is done with ball rolling machines like these
During rolling and drying, leaves are put into cloth sacks that are tightly bound. This bundle is then placed into a rolling machine that rolls it around in a circular motion, which causes the leaves to to ball up. After short intervals of rolling, the leaves are are then placed into tumblers to separate the leaves. They are then put into low-heat conveyor belt machines, which dry the leaves slowly.
Loose leaf oolong tea placed in a bag before rolling in a rolling machine
The rolling and drying process is repeated continuously for up to 12 hours. During each cycle, the leaves become more tightly rolled and drier. It is up to the experience of the tea maker, and the desired effect to determine when to stop the process.
Drying Oolong Tea leaves with a drying conveyor machine
Roasting
Depending on the type of tea being made, the tea leaves are then roasted. This is a post production process that is an art, or at least a professional skill, in itself. Tea roasters take into account everything from the environment in which the leaves were grown, to the time of harvest, the condition of the harvested leaves, how they were processed, and finally, how they are responding the roasting process to bring them to their optimal potential.
Roasting oolong tea leaves in a roasting oven
With traditional Oolongs, the more heavily oxidized leaves are roasted repeatedly, which not only removes all water content, but also "toasts" the leaf to varying degrees, transforming the flavor and consistency of the brewed tea. This is a significant factor in the making of a traditional artisan Oolong Tea.
Dong Ding Oolong Tea leaves
For greener high mountain tea, aka "gaoshancha" (高山茶), the significantly less oxidized leaves are most often left unroasted. However, there is a recent trend by cutting-edge high mountain tea producers to dry the leaves at the final stage of rolling and dry them more extensively by increasing the temperature in the conveyor belt drying machine and running the leaves through for a few extra rounds. Alternatively, tea merchants will put their purchases of fresh high mountain tea, aka “mao cha” through a singular post processing low temperature (70-80°C) brief “dry roast” in order to remove the remaining moisture from the leave. This stabilizes the composition of the leaves, giving them a better shelf life.
Packaging
When the final processing is done, the tea is packaged. Most tea producers in Taiwan package their own tea in bulk vacuum sealed bags of 18 kg to sell to wholesale customers who source tea direct from the factory on a seasonal basis. Others send their teas to local packaging facilities to be packaged into retail sized vacuum sealed bags, which they will then market as their own private brand.
See how tea is packaged in retail bags in the video below.
Loose leaf tea packed in vacuum sealed bags
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