Tea Processing
Apples?
Yes, apples.
To better understand the processing of teas, think about a piece of fruit, like an apple. Apples will begin to brown after they’re picked, even when left alone. If you cut or bruise the apple, it will brown more quickly. This is called oxidation. Oxidation happens when the enzymes in the fruit interact with oxygen, after the cell walls are broken apart.
The same thing happens to the tea leaf. Oxidation is the most crucial part of defining the different types of teas. It can happen quite quickly if the tea leaf is rolled, cut or crushed during processing, or more slowly if left to natural decomposition.
The thing that stops oxidation is heat. Think about the apples again. If you bake the apples whole or sliced in a pie, the apples will not turn brown. This is because heat at or over 130°F stops enzymatic activity and oxidation. The apples will look as fresh as when you first put them in the oven.
How do you like those apples?
Tea Processing Styles.
The production of tea falls basically into the following two production styles: Orthodox style and Non-Orthodox style, also called the ‘CTC’ or ‘Crush Tear Curl’ method.
Orthodox Production: This includes the basic tea production steps which are universal in nature. It starts with Plucking, Withering, Rolling, Oxidation and ends with Drying or Frying. These steps can be adjusted depending on the style of tea being produced.
- Uses the whole leaf, and typically only the top 2 leaves and the bud, and no more than the top 4 leaves.
- Trained tea artisans carefully roll and handle the leaves just enough to produce a certain flavor.
- Leaves vary in shape and size and are never intentionally cut or torn.
Non-Orthodox Production: This is also known as the ‘CTC’ or ‘Crush Tear Curl’ method style of production. This is actually a very different type of process wherein all the basic orthodox production steps are being performed but much more rapidly. This method is much faster than the orthodox ones and was specifically invented for the black tea industry.
- Uses the entire plant, including bud, leaves, and stem.
- All of which is placed in a machine and macerated (crushed, torn and curled), then rolled into little pellets and oxidized.
Harvesting & Plucking.
The tea leaves are harvested on a regular basis at intervals ranging from 5 to 8 days from each field. During quality periods (know as the First and Second Flush), only two leaves and a bud are picked – this is called fine plucking, resulting in high quality teas. At other times, three or four leaves and a bud are plucked – this is called coarse plucking. The plucked leaves are collected into bamboo baskets, taking care that they are not crushed by overloading the baskets. Once the tea leaves have been plucked, they are processed immediately. In order to maintain the freshness of the tea leaves, the leaves may be sent from the fields three to four times a day.
Withering & Steaming.
First, foreign matter is eradicated from the harvested leaves. The leaves are then weighed and withered, which involves laying the tea leaves out to reduce the water content and develop the aroma and flavor compounds in the leaves.
Withering times can vary from 18 to 24 hours depending on the moisture content and by the type of tea being made. Controlling withering means closely monitoring humidity, temperature, and airflow over time. The longer the wither, the more aroma and flavor compounds develop.
Properly withered, the leaves give off a fragrant aroma. The density of the withering leaves is also monitored to ensure they wither evenly. The withering process is complete once the tea leaves have achieved a desired percentage of water-loss, which is determined by the final weight of the leaves after withering or by the flaccidity and changes in the aroma of the leaves.
White, oolong, black and pu-erh teas are withered, while with green tea, leaves are steamed instead of withered to arrest the oxidation of the leaves so that they remain green.
Rolling.
Rolling is a process where rollers are used to rupture the cell walls of the withered leaves for oxidation of the polyphenols in the presence of oxygen from the air. In the past, the tea leaves were rolled by hand (and apparently foot – see picture at right) but today it is done by placing them on a rolling machine which rotates horizontally. The rolling machines apply pressure on the leaf, and the table itself has battens and a cone at the center to twist the leaf. There are also the more modern “Rotorvane” machines, which also give the same twisting and turning effect. This process takes about 20 to 30 minutes.
This process transforms the appearance of tea leaves to thin and wiry making them eligible for the process of oxidation. Rolling also releases the juices and oils from the leaves, encourages a more uniform oxidation, and gives each tea its distinctive flavor.
Oxidation.
Oxidation refers to a series of chemical reactions which result in the browning of tea leaves and the production of flavor and aroma compounds in finished teas. The process of oxidation is one of the most crucial processes in the manufacturing of the tea, simply because it determines the tea’s color, taste and strength.
Oxidation occurs best between 80-85°F and is slowed, nearly to a halt at 140-150°F. The tea leaves are then left in open air at temperature of 78°F for two and a half hours. During this time, the enzymatic reaction takes place inside the tea leaves, changing the leaves’ color from green to beige, to a rich, deep brown. To make a tea with a lighter taste, the oxidation process is stopped when the leaves are light brown. For a stronger tea, the leaves will remain in the warmth until they’re rich and coppery.
One important note is that: “The greener the leaf, the less oxidized it is.” Black teas are usually described as being fully oxidized as the tea leaves are allowed to fully oxidize before they are heat-processed and dried. Green teas are minimally oxidized. After being harvested, they are quickly heated and dried to prevent too much oxidation from occurring that would turn the green leaves brown and alter their fresh-picked flavor. Oolong teas are usually described as semi-oxidized. The oolong tea oxidation process is stopped by pan roasting the leaves.
Drying or Firing.
After oxidation, the tea leaves are passed through dryers to reduce the water content to approximately 3%, halt the oxidation process and lock in the final flavor of the tea. The drying process takes about 20 to 25 minutes, and the initial temperature is about 120°F and is finished off at a temperature of 200°F to 220°F. The moisture content of the teas when drying is completed is approximately 2% to 3% and the coppery brown fermented tea particles are present.
References:
- The Making Of Tea, Harsh Maur, December 7, 2016, https://teafloor.com/blog/the-making-of-tea/