1. How Stopping the Enzyme Separates Green, Black, and Oolong Tea
According to documents from Saitama Prefecture, tea made by stopping the action of oxidation enzymes in the leaf is called "non-fermented tea," and green tea is the main example. If the enzymes are allowed to work to some extent, it becomes "semi-fermented tea," or oolong. If they work to the maximum extent, it becomes "fermented tea," or black tea. [1]
Black tea is produced in large quantities in India and Sri Lanka, while oolong tea is produced in large quantities in China as an intermediate tea between black and green tea. [2] It is important to note that "fermentation" here does not refer to the action of microorganisms, as it does in sake or miso. Instead, it refers to the action of the oxidation enzymes contained within the leaf. [1] Therefore, the difference between these three teas is simply a matter of when and how much the enzymes are allowed to work.
So, how does green tea stop the action of these enzymes?
2. Why Freshly Picked Tea Leaves Are Steamed First
The first harvest, known as Ichibancha, is typically picked from mid-April to early May. The peak season is often said to be around the 88th day after the beginning of spring, known as Hachiju-hachiya. [3] However, the picking time varies by region and is not the same day across the whole country.
The typical method of picking is called "one shoot, two leaves." Only the bud at the tip of the branch and the two small leaves next to it are picked. [3] According to the Ministry of Agriculture, Forestry and Fisheries, the production of crude tea begins by steaming the raw leaves to stop the activity of the oxidation enzymes. This steaming step is considered a critical process that determines the quality and taste of the tea. [3]
The steaming time is about 30 to 60 seconds for standard Sencha, and around 120 seconds for Fukamushi (deep-steamed) tea. After steaming, air is blown onto the leaves to remove surface moisture and cool them down. [3] If the enzymes are stopped, the color should remain green. However, the steamed leaves are full of moisture and cannot be drunk as they are. The next step is drying these wet leaves.
3. How Rolling and Drying Remove Water from Steamed Tea Leaves
After steaming, the leaves are dried while being rolled in the following order: "Aramomi" (rough rolling with hot air), "Jūnen" (rolling under pressure without heating), "Nakamomi" (medium rolling with hot air), "Seijū" (fine rolling in one direction to shape the leaf), and finally drying. [3]
The water content does not decrease in a straight line. According to a process chart from Mie Prefecture, the moisture in the leaf drops as follows: about 78% right after steaming, 50% after rough rolling, 50% after Jūnen, 26% after medium rolling, 13% after fine rolling, and 4% after drying. [4] Interestingly, the water content hardly decreases during the Jūnen step. This step is for making the moisture uniform, not for drying. The water drops significantly during rough rolling and medium rolling, which use hot air. The long, thin shape of the tea leaf is formed around the fine rolling stage. [4]
How much does the weight decrease? The moisture after drying is about 4% in the Mie Prefecture example and about 5% in the Ministry of Agriculture, Forestry and Fisheries data, so we can estimate it at about 4–5%. [4][3] Using these numbers for a derived calculation: 100g of raw leaves with 78% water contains 22g of solid matter. When the water drops to 4%, the solid matter makes up 96% of the total weight. So, the total weight is 22 divided by 0.96, which is about 23g. This is roughly one-quarter of the original weight. Note that this is a calculation based on the assumption that only water is lost, not a direct figure from the sources.
Once dried, is the green tea finished?
4. What "Crude Tea" Is and Why It Is Not Yet Finished
According to the Ministry of Agriculture, Forestry and Fisheries, drying the tea leaves to a moisture content of about 5% allows them to withstand long-term storage and creates the specific aroma and flavor of tea. [3] This state is called Aracha, or crude tea. Aracha then goes through finishing processes such as sieving, cutting, roasting, and blending to become the final product. [3]
Drying has two meanings. Reducing moisture is not just for preservation; it is also a step that creates flavor and aroma. The flow of steaming, rolling, and drying can be read as a process that stops the enzymes, locks in taste and scent, and shapes the leaf into a form that lasts.
So far, we have looked at what happens after picking. But are there ways to change the taste before picking?
5. How Covering Tea Plants for About 20 Days Makes Gyokuro
In Saitama Prefecture, documents explain that Gyokuro is grown with a cover for about 20 days before harvest, while Kabusecha is covered for about 7 days. After this, they are steamed, rolled, and dried in the same way as Sencha. [2] The number of days for covering varies by region and method, so it is best to think of it as "about."
Why does blocking light change the taste? According to Mie Prefecture, covering the plants suppresses the conversion of theanine into catechins, resulting in less bitterness and more sweetness. A unique aroma called "Kabuseka" also develops. [5] A document from Kyoto Prefecture explains that tea made by blocking light has a vivid green color and a mellow umami and sweetness not found in open-air Sencha. [6] However, if the plants are covered for too long, photosynthesis is restricted, and the tea plants' vigor may decline. [5]
Matcha is not rolled. Leaves from a covered tea garden are steamed and dried without rolling to make "Tencha." Grinding Tencha into powder with a stone mill creates Matcha. [2] Even with the same steamed leaves, whether you roll them or not creates a different tea.
After reading this, you might want to see actual tea leaves.
6. How to See the Rolled Shape of Sencha Leaves at Home
If you have Sencha tea leaves at home, put a few on a white plate and look at their twisted, thin shape. This shape was created during the fine rolling process. [3]
Next, ask an adult to pour hot water into the teapot. Wait a little while, then spread the leaves from inside the teapot onto a white plate. Because the water is hot, please leave the handling to an adult. You might find small buds and leaf shapes among the spread-out leaves. If you find them, it may have been picked using the "one shoot, two leaves" method. However, not all tea leaves will show this clearly.
If you want to read the original sources, the entire process is summarized in the Ministry of Agriculture, Forestry and Fisheries feature article "Japanese Tea." The changes in moisture are on the Mie Prefecture Agricultural Research Institute page, and the covering of Gyokuro is on the Mie Prefecture Extension Center page. [3][4][5]