In our last blog, we learned about the science involved in the actual tea leaf. Now, we explore the science behind man’s manipulation of the tea leaf through processing. There are five main processing steps performed at origin: plucking, withering, rolling, oxidizing, and firing.
Did you know that even the best practices for growing and cultivating tea can be ruined in the processing steps? These steps occur even before the tea ever leaves origin. Understanding the science behind each step requires decades of training. Those that are skilled enough to fulfill this life journey, are the true Tea Masters in our industry.
The first step, plucking, is the act of harvesting the fresh new growth or flush. The plucking standard is determined by both the condition of the plant and the type of tea being produced. This can range from just the unfurled leaf bud to one-to-four leaves. However, for most teas, two leaves and a bud is the typical standard. The concentration of healthful Polyphenols declines as the leaf ages, so the older the leaf the less potential health benefits.
A fine plucking of the bud and the first leaf ensures higher caffeine levels. That means younger leaves contain more caffeine than older leaves. Increased temperature in the collection basket accelerates the degradation and lowers the overall quality of the leaf, and any breaking of the leaf during transportation encourages oxidation. This means time is critical in the plucking stage since nothing can be done until the tea reaches the factory.
Younger tea leaves contain more caffeine than older leaves.
Did you know that withering begins the moment the tea leaf is plucked? Withering is the process of reducing the moisture content of the leaf, to make it more pliable, and to breakdown large complex molecules into simpler molecules. Once the tea arrives at the factory, workers start the second step, controlling the withering.
Physical withering reduces the moisture content by about 50% and concentrates the cellular compounds left behind. Additionally, the leaf becomes more pliable for the next production steps. Chemical withering changes the chemistry in the leaf that contributes significantly to the teas color, aroma, and flavor. Controlling this step is more art than science. If too much moisture is left in the leaf, the tea becomes moldy. If the tea withers too long, then the oxidation could be inhibited due to enzymes not being able to bond with polyphenols. Depending on the type of tea to be made, the weather, and machinery, this process can take from one hour up to two complete days.
Controlling withering is more art than science.
Did you know that the goal of rolling is to break open the cell walls within the leaf and dismantle the cellular organelles within the leaf tissue? Once the tea has reached the right moisture level, it is transported to the nerve center of the factory, the rolling room, for step three. During this process, two essential compounds are released. Polyphenol Oxidase releases from the cytoplasm and polyphenols release from the cell vacuoles. Rolling is also responsible for shaping the leaf. Whether it be flattened, curled, semi-balled, twisted, etc. the leaf shape has been perfected over centuries to preserve the essential oils within the leaf. These essential oils contain the volatile components that make up most of the aromatics of the tea and part of the tea’s taste characteristics.
Did you know that oxidation is a natural chemical process? This is what turns the green tea leaf into shades of brown and black, similarly to when an apple turns brown after it is sliced, or falling leaves in Autumn. During oxidation, the color, flavor, and aroma are produced which are important to oxidized teas like black tea and dark oolong varieties. Technically, oxidation begins the moment cell disruption occurred; however, during this processing step, oxidization is controlled to produce specific types of tea.
Polyphenol Oxidase enzyme, which was released during rolling, catalyzes the oxidation process with the chemicals in the tea and oxygen in the air. With the help of this enzyme, polyphenols quickly oxidize into a compound that further reacts with the amino acids in the leaf, creating melanin, which is brown in color. This enzymatic browning oxidation is critical to the development of aromas and flavor compounds found in partially oxidized oolongs and fully oxidized black teas.
Did you know that heat permanently inactivates the enzyme responsible for oxidation? During the final processing step of firing, two important objectives are obtained. The first is to stop the oxidation process and the second is to remove much of the remaining moisture from the leaf to make the product shelf-stable. By firing the teas, heat is applied quickly to discourage rapid oxidation, but not too fast that it will burn the leaves.
To make tea shelf-stable for transport, it is essential that moisture is reduced to a level of about 4%, as additional moisture is gained during transit. A level below 10% is required to make the tea shelf-stable enough to be enjoyed for years. On average, 100 pounds of fresh tea yields about 22 pounds of finished tea.
Although not all teas go through each of the above steps, the type of tea determines the processing methods used. To the right, you'll notice a quick reference chart of the five basic tea types and the typical processing steps that occur.
That simple tea leaf is actually not so simple, after all! A lot of skill and understanding of the science behind tea is critical to ensure consistent tea quality, crop after crop. Personal knowledge in the tea plant can help you to be a better tea developer, purchaser, and cupper.
Thirsty for more? The #teaexperts at Hula Consulting can help with your tea education courses, ingredient sourcing, and more! Email to Scott@HulaConsulting.com or call 561.600.7025 to get started today.