When we discuss the differences among the various categories of tea namely: green, white, yellow, oolong, black and dark or ‘post-fermented’ teas, a recurring criterion is the level of oxidation. One key process that affects this is shaqing (杀青) or fixation.
Shaqing is literally translated as “kill-green”, a translation that gets the meaning across.
The Chinese Tea Dictionary (中国茶叶大词典), edited by the well-respected Chen Zong Mao(陈宗懋), describes shaqing as such:
“{The process where} …… destruction of the enzyme activity through high heat, preventing the enzyme induced oxidation of polyphenol compounds…. Reduces the grassiness…… reduces moisture content….. Makes leaves pliable and suitable for shaping……[1]
It further goes on to describe proper shaqing as:
“杀匀杀透，忌红梗红叶”
Translation: “Kill evenly and completely, avoid red stems and leaves”
This is not an abstract from the Turner Diaries or some similarly veined writing- a reminder that “kill” here refers to the destruction of the oxidation inducing enzymes.
The second portion is indicative of an essence of shaqing that we will get to in a while- speed.
But we are getting ahead of ourselves:
What is the Purpose of Shaqing?
Fixation is an excellent translation of what shaqing is about- pinning down a fixed level of oxidation.
Shaqing is about fixing a predetermined level of oxidation by a quick, even and complete destruction of the polyphenol oxidase enzyme which causes enzyme induced oxidation.
*This statement reads like a mouthful and appears like there is redundancy but as we will see in the next section, the additional words are essential.*
Let us look at how this is applied in the various categories of teas:
What role does shaqing play in each category of tea?
Category of Tea Shaqing? When
Green tea Yes Initial stages
Yellow tea Yes Initial stages
Dark tea Yes Initial stages
Oolong tea Yes After zuoqing
Black tea No NA
White tea No NA
A note here, ‘initial stages’ means shaqing is done before rolling or menhuang (in yellow tea). It may take place after 摊放 (tanfang) which is best translated as ‘setting down’, a process similar to but distinct from 萎调 withering. This will be explained in a separate post.
Performing shaqing at the initial stages fixes the level of enzyme induced oxidation of green, yellow and dark tea at a negligible level.
In yellow and dark tea though, there is oxidation induced at the menhuang and wodui stages which occurs after shaqing which is not related to the oxidation of polyphenols.
Oolong tea is more interesting in that shaqing takes place after zuoqing (做青)[2] when a certain level of oxidation has already been induced. Shaqing is performed to fix the level of oxidation, which is not as straightforward as we will see later, in order to maintain certain desired characteristics in the tea.
Black tea does not undergo shaqing and the oxidation is ultimately stopped by drying.
White tea too does not undergo shaqing but as it is ‘un-oxidized’, where ‘oxidation’ refers to the production stage[3], and ‘un-rolled’[4], the oxidation is natural and minimal.
How is shaqing performed?
By the Tang Dynasty, as evidenced by Lu Yu’s The Classics of Tea (茶经 Cha Jing), the shaqing of that era was by steaming. This later spread to Japan which continues to form the basis of how Japanese green teas, as well as mass produced Chinese green teas, undergoes shaqing. Of course instead of using firewood, modern steaming machines have been invented and produced, especially in Japan.
By the Ming Dynasty, Chinese production gravitated towards wok-roasting (also translated as pan-firing) shaqing which enhances the aroma but requires greater level of skills.
The first two are the most common methods but in recent years, experimentation has commenced with infra-red and microwave.[5]
What are the main challenges in shaqing?
Let us look at the fundamentals[6]:
i) Shaqing stops oxidation via destruction of the polyphenol oxidase enzyme with high heats, specifically 85⁰C and above
ii) Oxidation is induced by heat and doubles with every 10⁰C increase in heat. It is believed that this peaks at temperatures of 50-60⁰C
In a rather ‘duh’ moment let us state the obvious third point:
iii) In order to heat the leaves from room temperature, ~20-28⁰C for tea producing areas, to 85⁰C, you are going to increase the temperature of leaves to a point when oxidation activities are at their peak.
Therein lay the challenge of shaqing, heating quickly, completely and evenly such that the level of oxidation is maintained at levels intended.
Failure to do so could result in a non-green green tea which I wrote about previously and loss of ECGC and other polyphenol compounds.
Not to mention a lack of loss of briskness associated with good green tea.
The same applies for oolong tea where zuoqing induced level of oxidation will produce certain characteristics which a skilled producer will want to fix.
[1]中国茶叶大词典 page 367, author’s translation
[2] Zuoqing is often translated as partial oxidation, which though technically accurately, is misleading as it implies it is merely a scaled down version of the oxidation stage in black tea. Such an implication demeans the considerable skills and discretion oolong tea producers labored to master.
[3] Oxidized which was used to be referred to as fermentation, can be used both for the chemical process- i.e. the effect of oxygen on polyphenols and the production stage- i.e. oxidation stage in production of black tea which oxidation is deliberately induced.
[4] Rolling or shaping (揉捻 Rounian) is a stage which occurs in every other category of tea. More than aesthetics, the destruction of cell structure induces oxidation which is why it is performed after shaqing for all other categories of tea except black tea.
[5] 制茶学 by 安徽农学院 page 90
[6]制茶学 by 安徽农学院 page 91