How are different types of tea processed and classified?
Tea processing is an art and the process plays an important role in determining the final flavour of the liquor. Through processing, the leaves from the tea plant Camellia sinensis are transformed into the dried leaves for brewing tea. The classification of tea into its various categories is based on the kind of process involved in making it. The four most basic steps for processing tea involve oxidation of leaves, stopping of oxidation, allowing the formation of tea and then comes the drying process.
The variations of tea are obtained from experimenting with either or all of the steps mentioned above. The time of plucking tea leaves and the method of plucking also plays an important role in determining the final outcome. Most methods of processing have their origin in China and they are continued to be practised till date. From the same plant, it is possible to derive as many as six different types of tea — Green tea, yellow tea, White tea, Oolong tea, Black tea and post-fermented tea. Within each of these categories, there are even more classifications based on other factors.
In this article, I will walk you through some of the basic steps of tea processing and help you understand what exactly happens in each of these steps.
Contents
Step 1: Plucking
Tea flushes consist of a terminal bud along with two young leaves. The tea flushes along with tea leaves are hand-picked twice a year. Hand-picking is the best method for plucking though in some cases machines may also be used for the same process. When machines are used there are more broken leaves than whole leaves which reduce the quality of tea. However, through picking the perfect time for plucking, machine-plucking can also be used to get good results. Time of plucking is mostly in early spring and early summer but depends on the location as well.
Step 2: Withering\wilting
As the leaves are plucked, they begin to undergo withering through a process known as enzymatic oxidation. In this process, the water content of the leaves get reduced by about 30 per cent and it undergoes a slight amount of oxidation. Wilting is a natural process but the leaves can be put under the sun or in a place with a cool breeze to facilitate the process. In some cases, the leaves are laid on troughs and hot air is forced from underneath.
More than a quarter of the leaves weight is lost in this process. This step of tea processing has a contribution to overall taste also as it is this process in which the protein content of the leaves is broken down into free amino acids. This also increases freed caffeine content in the leaves. Both of these changes contribute to the overall taste.
After this process, the leaves appear limp and soft enough for rolling. The duration of the withering process has an effect on the final appearance of leaves as shorter durations results in greener and fresher leaves and longer durations lead to darker and more aromatic leaves.
Step 3: Disruption
Disruption is a process that is used to facilitate oxidation. In this process, tea leaves are bruised at various places. This process is also known as leaf maceration. This is done to break down the structures within the leaf which in turn allows the mingling together of various oxidative enzymes. The secretions released from leaves structures on disruption also aid in the oxidation process.
The disruption of tea leaves is done by shaking and tossing the leaves.
Step 4: Oxidation
There are some forms of tea like Black tea which require oxidation and hence this is one of the most important steps in their formation. For oxidation, the leaves are left in a temperature-controlled room where they turn darker due to oxidation. This is an important step for the formation of tannins. The tannins are produced when the chlorophyll present in the leaves is enzymatically broken down. Oxidation leads to the formation of important properties of tea like liquor colour, strength, and briskness. The percentage of oxidation leads to various types of tea. For instance, light Oolong tea has oxidation in the range of 5 to 40 per cent and Black teas are 100 per cent oxidized.
Though the leaves begin to get oxidized as soon as they are plucked, it is in this stage that Polyphenolic Oxidase begins to develop in leaves.
Step 5: Fixing
Fixing process is also known as ‘kill-green’ because it is the step in which controlled browning of leaves happens through the application of heat. The other steps in fixing involve steaming, pan-frying, baking and other forms of heating. Depending on the method of heating, the tea has different flavours. For instance, pan-fired teas have a more toasted taste while the steam heated teas have a more vegetal flavour.
This steps deactivates their oxidative enzymes and also removes unwanted scents without damaging the flavour of the tea.
Step 6: Sweltering
This process is done to produce yellow teas only. In this step, the tea leaves after oxidation which are still a bit damp are put in a container and slightly heated. Through this process, the green leaves turn yellow. The leaf chlorophyll transforms and gives the final blend a greenish-yellow colour. The heating process is done at the normal human body temperature for about six to eight hours. This leads to changes in amino acids and polyphenol contents of the tea. Yellow teas have a unique taste owing to this process.
Step 7: Rolling
Rolling is the process that gives the tea leaves the tight shaped form in which we see them in the final state. The procedure involves gentle rolling of leaves to enable it to take forms such as wiry, kneaded, spirals or tight pellets. The rolling process causes certain sap, essential oils and juices to squeeze out of the tea leaves which further intensify the flavour. They are usually rolled tightly to retain their freshness. The rolling process is done by hands or through machines which cause the tea leaves to wrap around themselves.
Step 8: Drying
Drying is done in order to make the final processed tea moisture-free. Hence, drying enhances the flavour and increases shelf life. The various processes of drying are panning, sunning, air drying and baking for a controlled period of time. Baking is one of the most common processes here. Ideally, the drying process brings down the moisture content of tea to less than 1%. The duration for which drying is done is important because if drying is done too quickly, it may lead to harsh and abrasive tea.
Step 9: Ageing
Also known as curing, this step of tea processing is not always required. In only certain cases, tea might require an additional stage of fermentation and baking to reach their drinking potential. Chinese Pu-erh is an example of a tea that is aged and fermented like wine. It is often bitter and harsh in taste but becomes sweet and mellow through fermentation by age or dampness.
Similarly, Oolong tea is also sometimes aged by firing over charcoal. Flavoured teas also required this step.
Tea is classified into their types based on the difference in their processing steps. The table below gives an overview of how various forms of tea is processed.
As shown in the above image, Green tea is processed through the steps of withering, fixing and drying. It does not involve the step of oxidation and rolling. Hence Green tea has a higher quantity of catechins and less quantity of caffeine as oxidation causes the loss of catechins and the gain of xanthines (caffeine compounds).
White tea is even less oxidized and has many health benefits due to a lack of oxidation.
However, this is not to say that the lesser oxidized forms of tea are better. All forms of tea have different types of health benefits. Black tea, which is highly oxidized contains a higher quantity of caffeine which is a stimulant.
Tea producers use special methods to initiate, fix, or even prevent oxidation in order to produce different flavours in a finished tea and inherently, different types of tea.
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