The Process of Transforming Tea Leaves

Black and Semifermented Tea (Oolong)

1. Withering - The leaves are exposed to hot air for several hours in order to reduce their water content by 50% to 60%. This step starts to free up the enzyme responsible for oxidizing the leaf (fermentation). It also softens the leaves, preparing them to undergo subsequent operations without breaking. The leaves must not be broken or bruised, except for certain types of tea where this is done in a precise and controlled fashion.

2. Rolling - The leaves are rolled (by hand or mechanically), allowing the essential oils to spread and to impregnate the buds. The aroma of the tea depends on these essential oils.

3. Sorting - A calibrated screen is used to sort the tea. The smallest leaves go directly to the next stage, while the larger, tougher ones undergo a second rolling.

4. Fermentation - Entails the chemical reaction of the leaves and their components (polyphenols) with air, humidity, and heat. This is a crucial moment, one in which the aroma, bite, and color of the tea are determined. If this step is stopped too soon, the tea is greenish, and can have a metallic after-taste; if it is fermented too much, it becomes sweetish and loses both quality and aroma. For the oolongs, which are semifermented teas, this step is abbreviated.

5. Firing - The characteristics of the tea become fixed at this stage. Drying the leaves in the oven stops the fermentation process. If the leaves are not dried enough (if more than 12% humidity remains), the tea may be attacked by mould. If they are dried too much (if less than 2% to 3% humidity remain) the result is a tea without aroma, since the aroma-carrying elements remain largely insoluble.

6. Grading - The leaves are separated by size or grade. This operation also cools and aerates the leaves. Once this process is complete, 100 kg of fresh leaves will have yielded 20 kg of black tea.

Soluble tea is a black tea that has undergone the usual production steps but that is dried even further and reduced to powder. This type of tea has the advantage of being easier to crate and ship for export. It is also ideal for the two great tea innovations of the 20th century: iced tea, and the tea bag.

Green Tea

1. Firing - The leaves are placed for 20 to 30 seconds in large iron basins heated to about 100o Celsius. This operation destroys the enzyme that causes fermentation. The leaves, then, remain green. In Japan, this process is accomplished by exposing the leaves to steam.

2. Rolling - As for black tea, the smaller and more tightly rolled the leaf, the more robust the tea, as more components are released.

3. Drying - This allows some evaporation of the water contained in the leaves to prevent mould.

4. Sorting - This is the step where the grades are separated out. Just as for black tea, the process uses sieves or screens of different calibers.

©1996: Centre d'histoire de Montréal
Picture source: Le Tao du thé en Chine, Taïwan 1983