Knowledge of tea rolling

Tea rolling refers to the process in which tea leaves are rolled into strips under the action of force, and the leaf cell tissue is destroyed, resulting in moderate overflow of tea juice. It is an important process for the formation of various types of tea and the formation of taste and aroma. The degree of rolling is usually measured by “cell tissue damage rate”, “strip rate”, and “broken tea rate”. When rolling, it is important to distinguish between hot rolling and cold rolling, and to pay attention to the influence of rolling time and pressure on rolling during operation.

Hot and cold rolling

The so-called hot rolling refers to rolling the withered leaves while they are still hot, without cooling them down; The so-called cold rolling refers to the process of rolling the green leaves after they have been taken out of the pot and allowed to cool for a period of time until the temperature of the leaves drops to room temperature. Rolling allows the contents of leaf cells (such as proteins, pectin, starch, etc.) to penetrate the surface of the leaves. These contents have viscosity at a certain moisture content, which is beneficial for rolling tea leaves into strips and further fixing their shape during the drying process. Leaves with different levels of age and tenderness have different branching characteristics. Leaves with high tenderness are prone to forming strips when rolled due to their low cellulose content and high pectin content; Old leaves contain a high amount of starch, and rolling them while they are hot is beneficial for the starch to continue gelatinization and mix well with other substances, thereby increasing the viscosity of the leaf surface. At the same time, under the action of heat, cellulose softens and easily forms strips. But the disadvantage of hot rolling is often that the leaf color is prone to yellowing and there is water stagnation. Therefore, for tender leaves, they are prone to forming strips during rolling. In order to maintain good color and aroma, cold rolling should be used; For mature old leaves, rolling them while they are hot can achieve a better appearance. Although hot rolling has an impact on color and aroma, older leaves already have a lower aroma and are darker green. Hot rolling loses some chlorophyll, which not only has little effect on their color, but sometimes makes the bottom of the leaves brighter. Therefore, older leaves should be subjected to hot rolling. The commonly seen fresh leaves with one bud, two leaves, and three leaves are of moderate tenderness and should be gently kneaded. The green leaves should be slightly spread and kneaded when they are still warm. The mastery of hot and cold rolling should depend on the specific situation.

Rolling time and pressure

The two are closely related and should be considered together, emphasizing only one aspect is not enough. Often, there is a situation where the rolling time is not long, but due to excessive pressure, the stems and leaves separate, and the rolled leaves break before they become strips. The rolling of leaves should achieve a certain cell breakage rate while maintaining the integrity of the strands, and the strip rate should meet the specified requirements. The tender buds and pointed seedlings should be preserved and not broken. In addition to the appropriate amount of leaves, it should be “time must be ensured and pressure must be appropriate”. If the pressure is not appropriate, especially if it is too heavy, the rolling effect will inevitably be difficult to guarantee. Because under excessive pressure, the buds and leaves will inevitably break and shatter after a certain period of time. Although the rolling time for advanced leaves is set at 20-30 minutes, it is generally not advisable to apply pressure or only light pressure can be applied; If this type of advanced leaf is subjected to excessive pressure, it will result in incomplete tea strips and broken seedlings after 15-20 minutes of kneading. So, when kneading tender leaves, the time must be guaranteed without applying pressure or applying light pressure, and the kneading time cannot be too short. This is an important means to ensure that “it needs to be thoroughly kneaded, continuously broken into strips, and kept sharp”. On the contrary, rolling older leaves is difficult to meet the rolling requirements without applying heavy pressure.

In order to improve efficiency and reduce labor intensity, multiple assembly type tea roller and fully automatic tea rolling production line have been developed, which can achieve automatic opening, weighing and feeding, closing, pressurization, and discharging throughout the process. The process parameters can also be adjusted to make the rolling quality more controllable. By using PLC automatic control technology and adopting a multi machine linkage form of rolling and twisting, continuous automation processing of multi machine feeding and rolling cycle operation has been achieved. But this type of rolling and twisting unit still needs to go through shutdown and blade feeding, and only achieves intermittent continuous rolling.

TIPS:Green tea rolling requires mastering the principle of gentle rolling of tender leaves and heavy rolling of old leaves
The weight, duration, and method of rolling have a significant impact on the quality of green tea. If too much force is applied, a large amount of tea juice will overflow, and some flavonoids are easily oxidized to form black brown substances, which is detrimental to the color of tea leaves; At the same time, due to the increased rate of cell damage, the soup color is thick but not bright enough. If the kneading time is too long, polyphenolic substances are prone to oxidation reactions at room temperature, causing the soup color to turn yellow; However, insufficient rolling results in a lighter taste and color, which cannot form a tight and linear shape of green tea, reducing its external quality. Therefore, different rolling and twisting methods during processing have different effects on the quality of tea.