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How does green tea processing stop the oxidation of tea leaves?

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Neatly planted rows of green tea bushes stretch across rolling fields with Mount Fuji, capped with snow, rising in the background in Japan. — tea Rows of tea (*Camellia sinensis*) growing in Japan, with Mount Fuji in the background.

To produce green tea, the oxidizing enzymes within the freshly plucked leaves must be inactivated to prevent the chemical reactions that typically darken tea leaves. This is achieved by applying heat to the leaves before they undergo rolling.1

Specifically, the leaves are processed using one of two primary methods:
* Steamblasting: The leaves are treated with steam in perforated drums.1
* Roasting: The leaves are heated in hot iron pans.1

By using these methods to kill the enzyme known as polyphenol oxidase, the polyphenols in the leaf are prevented from oxidizing. Because these polyphenols remain colorless, the processed leaf retains its green appearance rather than turning the dark brown or coppery color associated with fermented black tea. This process is essential for maintaining the unique characteristics of green tea, including varieties like matcha, which is also steamed to halt oxidation before being ground.12