All tea comes from the Camellia sinensis plant; however, where the tea is grown, the climate, soil conditions, altitude, etc., and how the tea is processed, determine the characteristics of the tea. 

There are two methods of processing tea: Orthodox used to make loose teas and CTC or Cut, Tear & Curl used to make bag teas.

Orthodox

In the traditional, or orthodox, procedure, the process used to make loose tea, the leaves must go through a process of Withering, Rolling, Oxidization and Drying.

• Withering: The objective of withering is to reduce the moisture in the tea leaf by up to 70%, depending on the region in which it's been grown. The tea leaves are laid out on wire mesh in troughs. Air is then passed through these troughs so that the moisture is removed in a uniform way. This process takes between 12 and 17 hours, until the leaves are limp and pliable and will roll well.
• Rolling: The tea leaves are then placed into a rolling machine, which rotates horizontally on a rolling table. This action creates the twisted, wiry tea leaves. During the rolling process the leaves are also broken open, which starts the third process, oxidization.
• Oxidization: Oxidization, otherwise known as fermentation, is an extremely important part of tea production. The process of oxidization ultimately creates the different types of tea,  black, green and Oolong. These teas differ in the amount, or lack of, oxidization. Black teas are fully oxidized; Oolong teas are partially oxidized; and green teas are not oxidized. It is oxidization that contributes the most to a tea's flavour, colour and strength. This stage is critical to the final flavour of the tea. If left too long, the flavour will be spoilt. To oxidize tea, the leaves are put into troughs or laid out on tables. Oxidization occurs when enzymes within the leaves react with the air and takes from between 30 minutes and two hours at about 26 degrees centigrade. It is during this process that the tea leaf changes from green, through light brown to a deep brown. Once the tea has reached the desired level of oxidization, light for a light liquoring tea and dark brown for a stronger liquoring tea, the leaves are dried (otherwise known as "firing the tea").
• Drying: To stop the oxidation process, the tea is passed through hot air dryers. This reduces the total moisture content to about 3% and the dried tea is ready to be sorted into grades before packing.

CTC - Cut, Tear & Curl

The CTC, or Cut, Tear and Curl, method was invented during World War II to increase the weight of tea that can be packed into a sack or chest. The CTC process follows that of orthodox manufacture up to the rolling stage. Instead of rolling the leaves, the CTC technique passes the leaves through a series of cylindrical rollers with hundreds of small sharp "teeth" that Cut, Tear and Curl. This creates a smaller granular type leaf, ideal for brewing from teabags. CTC does not alter the quality of the tea leaves. Following this stage, leaves follow the same processes of oxidization and drying as described earlier in this section

Black tea

Black teas are the world's most commonly produced tea. Like red wine, black teas are fuller bodied and have stronger flavours. The stronger flavours and deeper colours are a result of oxidization. Of the three major tea types (black, green and Oolong), black teas undergo the longest process of oxidization.

Green tea

When making green tea, the oxidization process is omitted, which allows the tea to remain green in colour and keep its very delicate flavour. In order to ensure that the freshly picked leaf does not oxidize, the leaves are either pan fried or steamed to kill active enzymes in the leaf before rolling. This prevents the air from interacting with any of the enzymes in the leaf, so no oxidization takes place. In China, some green teas are withered before being pan dried, but more commonly the withering process is omitted and the teas go straight to the rolling process.

Oolong tea

Oolong teas follow the same path as black teas, except that they are only oxidized for a very short period of time, creating the distinctive coppery edged leaf colour and a delicate flavour.