Tea Culture

Exploring the Science of Oxidation and How it Affects Tea

Our Wakoucha Mariko, a Japanese black tea. This tea could be considered full oxidized.

All the different tea types are made of the same plant (different cultivars but the same plant). White tea, green tea, yellow tea, oolong tea, black tea, post-fermented tea; they all come from the same plant, Camellia sinensis. As cultures are different across the world, so are the ways that people use the tea plant to create all the different types of tea. The different types of tea, if it is a Darjeeling black or a Fuding Yin Zhen, are created at least partially by manipulating the picked tea leaf. A part of this manipulation of the tea plant involves controlling the oxidation of the tea plant.

Right when the tea plant is picked, oxidation begins. Oxidation is defined as, “A reaction in which the atoms of an element lose electrons and the valence of the element is correspondingly increased.”In terms of tea production, the chlorophyll in the leaves is enzymatically broken down, and its tannins are released or transformed. The tea producer may choose when the oxidation should be stopped, which depends on the desired qualities in the final tea as well as the weather conditions (heat and humidity). Green tea, for example, goes through something called the “kill green” process almost immediately after picking the leaf. The picked tea leaves are heated to a certain degree which turns off the enzymes responsible for oxidation. This “kill green” process allows the tea producer to fix a tea to a certain level of oxidation. Here is a video of one of our staff collecting some freshly made green tea.

While green tea goes through it’s “kill green” process soon after it is picked, black tea is allowed to oxidize for an extended period of time before the enzymatic activity is ceased. The leaf is allowed to fully (or almost fully) oxidize, giving it a deeply red color, then it goes through the kill green process. For Oolong tea, the tea master has free rein to halt the oxidation of the tea they are making and isn’t really bound to any particular standards so far as the tea types are concerned. For oolong tea the oxidation can vary; some will be lighter in their oxidation and develop some milky, floral notes while others will have be allowed to oxidize for longer and resemble something closer to a black tea, develop some stone fruit and caramel notes. All this is to say that oxidation plays a huge part in determining the type of tea that is made.

We did a TikTok video covering this very topic, where you can how oxidant affects the look, smell, and taste of a tea, here is a look at it:

While a lot more can be said about oxidation and how it relates to tea, we hope that this blog post has inspired you to look at tea in slightly a different way. If you are new to tea, it might be fun for you to pick up some green tea, oolong tea, and black tea to see if you can notice any differences in color. Especially with oolong tea, oxidation level will vary and there are much more factors at play than just oxidation. That being said, the approximate oxidation level of a tea really determines which category of tea it belongs to and what you more or less can expect from drinking it.

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