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Microwave Fixation - The Future of Green Tea?

“Where do I kill-green? Well, I just use the microwave in my apartment.  That gets the job done just fine. Two minutes in there provides a perfect and complete fixation.” So spoke the retired biologist that once ran the tea department of Enshi’s top university. This was the second time we encountered the notion of ‘killing green’ with microwave heat, the first time being last year at a rather high-tech, government-supported facility in Anhui, Huifeng Tea, where they have started using similar machinery in yellow tea production. Later in Emei, Sichuan we encountered related equipment, freshly purchased this last year. Meanwhile, we have heard from producers in Enshi that the number of local factories that use this machinery has grown from just 2 last year to more than a dozen in 2024. Why make such a change? With upfront costs of more than 100,000 RMB, why would any factory in a bad year for tea make the transition to microwave production now?  

Kill green, the critical step in green tea production where leaves are subjected to a prolonged encounter with heat to limit further oxidization, is done in China almost exclusively with one of two pieces of equipment: a heated tumbler or large wok. With the exception of certain styles where woks are essential, like in Longjing, Golden Green, or Guapian, most of the green tea sold in China today goes through the kill green process in a tumbler. Tumblers have been the widely used in Chinese tea factories since as early as the 1950s. Woks meanwhile have been the hallmark of the cheapest, homemade green tea that is sold directly on street markets and street corners for many centuries. Now also, woks are being used in contexts where boutique “handmade” green tea is being marketed as a return to “original” or “authentic” production traditions, even in areas where green tea production is altogether new. The cost of wok fried green tea per unit can be anywhere from 3 to 5 times the cost of tumbler production, so it only makes sense for niche producers who already have connections with high-end clientele or elder farmers without better options who are making tea in the kitchen woks.  

In Enshi, theoretically China’s only bastion of green tea where Japanese imported equipment abounds, most green tea is still killed in a tumbler. Historically, the steam boxes that were used in Yulu production were more finicky and liable to produce accidental yellow tea than the tumblers introduced in the county and commune-run factories of the 20th Century. Older generations of coal or pellet-fired tumblers are however no match for the electric, fully-automated conveyor belt steaming equipment borrowed from Japanese sencha production. The latter “kills the green” more evenly, and produces a darker green color, and costs less per unit. It does not, however, do quite so good a job when it comes to aroma. Licensed Yulu producers in Enshi’s Bajiao, Taiyanghe, and Tunbao townships all agree that it is still the tumbler that does the best when it comes to producing that fragrant, nutty and milky scent desired from local green tea.      

With wok-fried tea virtually extinct in Enshi’s commercial production, the tumbler has continued to reign supreme. Although Yulu completely compliant with production regulations ought to be steamed, tumblers are still de facto used for most of what is sold as Yulu. For other styles like Maojian or Xiangcha, local producers almost exclusively use tumblers. That is, until now at least. Now, microwave equipment is increasingly being adopted for all of these styles.

There are a few reasons behind the new adoption. The most widely cited reason is, naturally, financial. Although this technology has been commercial used for more than a decade, only now is it clear that it has the potential to reduce production costs. Just like with the automated sencha-steamers, they are fully electric, meaning that producers can save on fuel costs. More critically however, this new generation of microwave machinery can help producers save on labor costs. While it takes years of experience to learn how to not blister or underheat green tea in a tumbler, microwave equipment does the job consistently and in just minutes. Gone could be the days of the tea master firing up the tumbler, checking the temperature with his hand, minding the pellet / coal furnace, and perhaps even running through a batch of throw-away tea to verify the heat is right. Hours of work from a specialized laborer can now be eliminated each and every day of the production season.

In the words of a cadre in Hubei Province’s Wudang Mountain: “before in the primitive(原始) method of manual kill-green, the whole process depended on experience. Now with this new equipment, we can better protect the environment, save on costs, and decrease the intensity of labor[1].” A tea producer Enshi’s Xianfeng County is quoted telling the local science and technology bureau saying that have switched to microwave kill-green to improve product quality, a sentiment shared by one Tunbao township producer who has spent a total of more than 500,000 RMB microwave equipment this year[2]. That is however chump change when compared to the producer in nearby Yichang that spent a total 10 million RMB on microwave and automatic packaging equipment the first year of Covid[3]. In a situation where producers are competing to lower prices in a moment of excess demand, such investments in automation will pay dividends to the factories large enough to afford it, while the smaller factories or those who have already invested big on direct management of tea fields will be less able to compete for the large wholesale orders from coastal China that make up the bulk of local tea revenue.  

The research I have found on China’s CNKI database does seem to back up the claim that microwave kill-green gets the job done more consistently and potentially even with superior aroma and taste outcomes. It is the instantaneous heating of both the inside and outside of tea leaves loaded into the microwave ovens that makes the process faster and more consistent than earlier methods. Critically, it has also been found to lower the phenol/ammonia ratio and raise the amino acid content of finished tea, which may contribute to a less bitter taste[4]. In a later study, tea polyphenols that also contribute to bitterness were found to have the lowest presence in microwaved green tea when compared to steamed, wok-fried or tumbler heated green tea[5]. These tea polyphenols are thought to be most prone to thermal degradation, and while they may make tea bitter, they are also one of the components in green with thought to have the greatest anti-oxidant and health benefit. This means that microwave kill-green equipment may be producing less bitter, consistently unburnt green tea at lower costs, but potentially with less of the health benefits some consumers may expect in green tea.

In the next few years, we will see whether or not there is a larger transition to microwaved green tea, or if this will be just a passing fad. In a country where wok-frying survives in many provinces and even the truly archaic method of wicker basket drying survives in at least Lu’an, it seems likely that the tumbler is not going to disappear anytime soon. Unless the glut of green tea on the market continues to drive down sales and wholesale prices, I suspect most producers will keep making green tea the same way they have for decades now.

 

[1] Hubei Daily. “Wuhan Tequ Juyazi Cun: Zhinenghua Xin Bangshou Zhuli Chaye Tidang Shengji” June 28th 2023.

[2] Enshi Science & Technology Bureau. “Xing Keji, Qiang Pinpai, Xianfeng Baicha ‘Xin’ ‘Zhi’ Piao Xiang.” April 17th 2024.

[3] Yichang Commercial Affairs Bureau. “Zhibo Daihuo: Yingxiao Moshi Quanxin Changshi.” April 15th, 2020.

[4]Liu Mengyuan, Cui Lidan, Xu Yangyang, Wang Jiguo, Liu Feng, Gong Zhihua, Xiao Wenjun.Effects of Microwave Fixation Process on Preserving Green Color and Reducing Bitterness in Autumn Green Tea. Journal of Food Safety & Quality 2022(07) 2152-2157

[5] Peng Ye, Gao Qinyan, Li Meifeng, Yang Yun, Huang Tao, Liu Jianjun Effects of Different Fixation Methods on Aminobuturic Acid Content and Quality Components of Huangjinya Green Tea.Journal Southern Agriculture 2023(10): 3020-3028.