Kill-Green in Tea Production

Have you ever wondered why Japanese green teas are so green? And why Chinese green teas are not as bright green, but are typically yellower? The reason lies in the processing steps for each tea and in particular the “kill-green” step of the processing some tea types.  The term kill-green is derived from the Mandarin shaqing (杀青), which means “killing the green.”

Kill-green is also referred to as “de-enzyming” or “fixing” and is a process of tea manufacture used to halt the oxidative browning of tea leaves by denaturing the enzymes responsible for oxidation–  polyphenol oxidase and peroxidase. Think of an apple, once it is sliced open, it quickly turns brown; however, the apples in apple pie are not brown because the heat used to bake the pie denatured the polyphenol oxidase and peroxidase in the apples and prevented enzymatic browning (same goes for potatoes, avocados, bananas, etc,).

In tea, the leaves must be heated to approximately 150 degrees Fahrenheit to halt oxidation. The longer it takes to heat the leaves to the temperature necessary for denaturing polyphenol oxidase and peroxidase, the more aromatics will develop. For example, green teas that are steamed reach this temperature more quickly than teas that are pan fired and as a result remain bright green and vegetal and lack a diverse aroma. Pan fired teas invoke what’s called the maillard reaction which is a form of non-enzymatic browning that produces toasty notes in a tea and finished tea leaves that are usually yellower in appearance. In general, most Chinese green teas are pan-fired (photo above), and most Japanese green teas are steamed (photo below). There are other methods for “killing the green” — sometimes a heated tumbler is used or an oven-like machine, while some teas are sun-dried and in this case, oxidation is halted not by heat, but by dehydration. The kill-green process of tea manufacture is commonly employed in the production of green, yellow, oolong, black tea when dried, and post-fermented teas.

This post is part of a larger post dealing with the initiation, control, and cessation of oxidation. It’s also part of a series of posts covering other individual processing steps: withering, oxidation and drying. And finally, my tea processing chart.

2018-05-15T08:40:37+00:00

About the Author:

Tony has been studying tea for over ten years and has traveled to many tea producing regions throughout Asia. His book, "Tea: A User's Guide" is available now.

13 Comments

  1. Tomas February 7, 2016 at 2:11 pm - Reply

    Hi! You are writing about the correlation between freshness and “greeness” of tea and the way how the process of oxidation is halted. How you explain for example the case of Bai Sha Lu where the oxidation is halted by steaming? Of course that it is a bit different to “classic” chinese green tea like Mao Jian or Long Jing – the taste is more flowery and so on but the main body of taste remains very similar.

    Thanks in advance for answer 🙂
    Tomas

  2. IM December 7, 2014 at 12:08 pm - Reply

    Greatly like your page. Congratulations! Quick question: is the steaming (vs. pan-firing) solely responsible for the grassy note in Japanese green teas, or is it also the lack of withering which retains the grassy notes? In one of your other articles I read that pan-firing releases grassy notes, thus is the lack of withering a reason for grassiness in Japanese greens? Thanks!

    • Tony Gebely December 8, 2014 at 12:05 am - Reply

      Thanks for your comment. Japanese green teas are withered for a short period. The vegetal notes in steamed Japanese green teas is largely due to the fact that steaming quickly halts oxidation but these notes can probably also be attributed somewhat to cultivar.

  3. Mei February 15, 2013 at 9:13 am - Reply

    Hi Tony,

    Can I share your article with my students? Your article is really helpful for them to comprehend the tea production.

  4. Richard Zhang June 4, 2012 at 8:22 pm - Reply

    Hi Tony:

    It is a good article. Especially impressd by your analogy of apple, very great! For your question, my understanding is that the “Qing” doesn’t refer to the color of the leaves but the aroma. That is to say the “Qing” in the name of ” Sha Qing” means”Qing Qi”(in Chinese, it means grassy aroma) instead of “Qing She”( green color).

    • Tony Gebely June 10, 2012 at 12:06 am - Reply

      Richard, thanks a lot for the information, this is great!

  5. Hannah May 31, 2012 at 6:27 am - Reply

    Hi, this is great information to learn because I deal with Chinese green teas on a daily basis but never green teas from other countries. So thank you for sharing this information with us!

  6. Nathan May 23, 2012 at 4:51 pm - Reply

    First of all, I’d like to say that It’s refreshing to come across educated tea dialogue originating in the US. I’ve been propagating tea culture in Austin, TX after returning home from many years in Asia–mostly in Taiwan–and it’s taken a lot of energy!

    After reading your article, I was scrolling down to make a very similar comment to Brandon. The Chinese word “青” refers to a blue-green “vegetal” color. It’s the same word use for leafy greens in Chinese, therefore I’ve always thought of it as referring to plant “life.” I didn’t know about sha-qing (殺青) specifically though, so this really shed a bit of light on some things I was wondering about myself–especially as to the flavor difference of the steamed Japanese teas versus roastedness of Chinese green.

    appreciate your work

    加油!!

    • Tony Gebely May 25, 2012 at 10:12 pm - Reply

      Nathan, Thanks a lot for the kind words. I’ve been researching tea for several years. I’m now working on a book as well. I looked up your blog and your work in Austin, very impressive! Keep spreading tea culture!

  7. Brandon April 23, 2012 at 3:28 pm - Reply

    Hi Tony,
    I think the misunderstanding comes from taking the common Chinese translation too literally.
    Shaqing translated as killing the green is probably good enough, but you have to consider that qing 青 is referring to something broader than the color of the leaves (which is in fact 绿 lu).
    Qing can mean raw, fresh, young, etc… So it is correctly referring to the fact that you are killing the enzymes or the rawness of the tea that leads to spoilage… the vegetative “greenness,” not the color of the leaf.

    • Tony Gebely April 23, 2012 at 3:32 pm - Reply

      Brandon, thanks for the information, twitter user: @xuetingni also just shared with me this interesting information: “The ancient Chinese dried bamboo strips over fire before writing on them, to prevent rotting and make them easier to write on this process was the original ShaQing, after drying the green skin is peeled off the bamboo strip for better writing surface sometimes people would write on green skin first, then peel the bamboo skin off to make amendments, literally killing the green.”

  8. Alex Zorach April 23, 2012 at 1:22 pm - Reply

    I think this is a great topic, and I think it sheds a lot of light on how to classify teas, as well as how the teas actually taste. When I started learning about the process of heating teas to stop the enzymes that cause oxidation, I feel like a lot of the distinctions between the different types of tea, and the relationships between their production and their flavor, aroma, and color.

    I’m not sure about your point about the grassy quality in tea though. All green teas have been heated during their production, yet I find many of them have a very potent grassy aroma, and in comparison, I find white teas (which have not been heated to the same degree) tend to have much less of this aroma.

    So I supect this grassy quality may actually arise to some degree from the production itself, which of course involves heating. The answer to this one may also be a bit subjective too, as people experience tastes and aromas differently, and they don’t necessarily mean the same thing when they talk about a “grassy” quality in tea. It’s much the same as how teas with very different aromas can both be described as having an “orchid” aroma (compare Tong Cheng small orchid, to Qi Lan oolong).

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