Have you ever wondered why Japanese green teas have a brighter green color compared to the typically yellower Chinese green teas? This difference in appearance is due to the processing steps and, in particular, the “kill-green” step used for each tea. The term “kill-green” is derived from the Mandarin shaqing (杀青), which means “killing the green.”
Kill-green is a process used in tea manufacturing to prevent the oxidative browning of tea leaves by denaturing the enzymes responsible for oxidation–polyphenol oxidase and peroxidase. Similar to how baking a pie prevents apples from turning brown, heating tea leaves to around 150 degrees Fahrenheit halts oxidation. The more time it takes to heat the leaves to this temperature, the more aromatics will develop.
Green teas that are steamed reach this temperature quickly and remain bright green with a vegetal taste and aroma. Pan-firing green teas, which is a common method in China, invoke the maillard reaction, producing toasty notes and a yellower appearance. Other methods for “killing the green” include using a heated tumbler, oven-like machine, or sun-drying. This process is used in the production of green, yellow, oolong, black tea when dried, and post-fermented teas.
This post is part of a larger post discussing the initiation, control, and cessation of oxidation, as well as other individual processing steps such as withering, oxidation, and drying.