When Europeans first became interested in drinking tea the only significant source available was from China. The Chinese were naturally very protective and secretive about their tea and would put forward misleading information about where it was grown, when it was harvested and how it is processed. One of these myths was that different types of tea were produced from different plants and this belief was sustained for many years. We now know, however, that regardless of type, whether it is green, white, oolong, black, yellow or dark, all true teas are produced from the leaves of the camellia sinensis plant.
In fact there are two main varieties of camellia sinensis recognised being camellia sinensis var.sinensis and C. sinensis var. assamica where sinensis and assamica suggest origins from China and India respectively. However, it is not as black and white as this may sound as some of China’s famous teas (such as Pu-erh tea) are made from the broader leafed assamica variety and the renowned Indian Darjeeling teas are produced from the leaves of the sinensis variety. Nowadays, there are many hybrids and numerous varietals that have been bred but essentially it is just the one plant responsible for the world’s favourite beverage.
So, if it is the same plant how come there are so many different types of tea? Fundamentally, it comes down to the way that the leaves are processed and the degree to which the leaves are allowed to oxidised (also sometimes referred to as fermented) during production.
For green tea there is no oxidation. Once the leaves have been harvested there is usually a short period where the leaves are left to wither but relatively soon after harvest they are subject to a process which is known as ‘kill green’. The purpose of this process is to kill the enzymes in the leaves that are responsible for oxidation and is achieved by the application of heat to the leaves. The way that this is done varies between producers and in different parts of the world and includes baking, frying or steaming, each with varying degrees of technological sophistication. Once ‘kill green’ has been completed the leaves experience several cycles of rolling and drying before the final product is completed.
At the opposite end of the spectrum is black tea which is left to completely oxidise. Once leaves are harvested they are left to wither for an extended period with the objective of reducing the moisture content in the leaves until they are soft enough for subsequent processing. The length of the withering stage will depend on temperature and humidity and may be as long as 14 to 20 hours. When it is judged that leaves have withered sufficiently they will be rolled for shape and to break the leaf cell walls in order to release the essential oils that will stimulate oxidation and give the tea its colour, strength, aroma and taste. The tea is then left to fully oxidise before the final drying, sorting and grading takes place.
In between green and black sit the oolong teas which, typically, experience anywhere between 10% and 70% oxidation. As this allows a reasonably wide range of possibilities, oolong teas can be found in the many shades between green and black with taste characteristics that are closer to one or the other. A typical oolong process involves sun drying and withering of the leaves before they are shaken to break the leaf edges to commence oxidation. The degree of oxidation is key to the appearance and taste of the final tea and when the desired level has been reached the leaves go through a ‘kill green’ process to bring the process to a halt. Oolong teas then go through many rolling and drying phases depending on the type of final leaf appearance that is required. In order to achieve the familiar ball or pellet shape leaf may require the leaves to be rolled up to ten times.