Wednesday, March 14, 2018

Wuyi oolongs: art and chemistry

Below, the introduction to the entrancing surrealist tea art of Julian Landa: photographs of the Wuyi mountains, transformed to remind us that Wuyi is where oolong originated—find the series at

Julian took the photos while on a pilgrimage to the Wuyi mountains with his wife, Cynthia Gold, renowned Tea Sommelier at L'Espalier in Boston (see my post of 2/7/18)  to experience first hand the extraordinary landscape and its famous teas.

To contemplate Julian's images, I brewed myself a Wuyi Rock oolong, Ma Tou Rou Gui from Horse Head Mountain via Verdant Tea ( Their website shows the fantastical rock formations and tea gardens captured by Landa's art—to me it was easier to imagine teapots in these mountains than horses' heads! 

The unbrewed leaves smelled slightly roasty and woody and offered a slight prickle in the nose. Nothing floral. The aroma of the brewed tea had the lovely full warm roasty wintergreen* characteristics of highly oxidized Wuyi mountain oolongs, but strangely no prickle. The flavor was also roasty and sweet, but after a slight delay you could sense the prickle in the throat that the smell of the dry leaf foretold. 

Here's the brew -- a dark oolong, quite roasty!

Verdant Tea describes this prickle as a "tingling cooling quality" that "seep[s] into the tongue after only a few sips and grow in intensity over each steeping." 

In the video on the webpage describing the tea, Li Xiangxi leads a class in Wuyi rock tea appreciation, where she calls the aftertaste "Yan Yun." She goes on to mention the aftertaste of Tie Guan Yin as "Yin Yun," and that of Tai Ping Hou Kui (a mind-blowing green tea that I will present to you in some other post) as "You Yan." **

Back to "Yan Yun:" Li Xiangxi states that, of the three aftertastes/resonances ("Yun"), Yan Yun is the most "opaque." She notes that the Emperor Qianlong described the "Yun" as "fish bones in his throat," a sensation that he apparently appreciated very much, despite the connotations. I sensed exactly what he meant when I tasted the tea. After a short beat, I felt this sharp though not unpleasant sensation in my throat that lingered for quite a while. 

Of course (being myself) I then asked what chemical compound(s) in the tea could cause this sensation? In order to answer this question, I first had to ask: is this sensation accompanied by hot (TRPV1 activation) or cold (TRPA1 activation)? Honestly I couldn't tell, though it did remind me of the catch in the throat that you get with a good olive oil, caused by activation of TRPA1 by oleocanthol. So I decided to carry out an experiment. 

I had just received a superb chocolate from Ben Rasmussen of Potomac Chocolates—the reward for having supported him in his Kickstarter campaign ( It was 70% Tumaco Columbia chocolate that tasted very warm and winey. If the chocolate cancelled out the catch in the throat, there would in all likelihood be a compound in the tea that activated TRPA1— chocolate has multiple compounds that would activate TRPV1 and turn off TRPA1. 

Here's the set-up half-way through the experiment, tea, wet leaves, and chocolate!

This experiment started me on the most exciting see-saw: first I tasted the tea, and got the catch in my throat, then tasted the chocolate—again a beat and the flavor of the chocolate filled my mouth and the catch disappeared, though I could still taste the roastiness of the tea. Then back to the tea and the catch came back, and then the chocolate and it this for several iterations.

I concluded that compounds in the tea activated TRPA1. 

So what could these compounds be? A paper published just this year provided the answer.*** It turns out that Wuyi rock teas have relatively large amounts of at least two distinctive compounds that activate TRPA1: quercetin and kaempferol.**** 

Below, graphs showing the quercetin and kaempferol content 14 Wuyi rock teas, from S Chen and colleagues. RG refers to Ruo Gui. As you can see, it does not have the highest amount of these compounds, but it has more than many.

Which raises the next question: why are these compounds present in higher levels in Wuyi rock teas, the only teas so far in my experience that give such a clear prickling sensation? Is it a question of "terroir?"

I don't know the answer to this question, but I present the following to support the "terroir" hypothesis, namely that the enzymes for the biosynthesis of these compounds require iron.***** Iron is abundant in the red sandstone of the eastern Wuyi mountains—it's what gives the rock of these mountains a slightly reddish hue, visible in Julian's photo/art above. 

Which brings me to another attribute given to Wuyi rock teas: minerality. The wine world has been discussing what people mean when a wine has minerality.****** According to Wendy Parr and her colleagues, minerality is characterized by a "fresh/zingy note." I have found that when people say "fresh" they refer to a cooling sensation, and when they say "zingy" the sensation is a kind of other words the effects you would get with activation of TRPA1. So it is likely that these compounds contribute to the minerality of Wuyi rock teas. 

Spent the day imagining a warm walk through Wuyi gazing up at the rock formations among clouds of tea, far away from the crisp cold snow here in Massachusetts. 

Hope you had a richly filled day, too!

===> On Amazon in paperback and Kindle: "Three Basic Teas & How to Enjoy Them"

* The wintergreen quality comes from the presence of methyl salicylate, which is produced as you roast tea.

** This video is well worth the watch. Li Xiangxi begins the tea tasting with hot water, declaring it sweet. Warmth activates TRPM5, the receptor/channel in taste bud cells that also transmits sweet sensations, so the brain interprets the experience as "sweet." She also talks about Western versus Chinese art, a vast topic, but one that I may poke at in a coming blogpost.

*** (Si Chen et al. Metabolite Profiling of 14 Wuyi Rock Tea Cultivars Using UPLC-QTOF MS and UPLC-QqQ MS Combined with Chemometrics. Molecules 2018, 23(2), 104; doi:10.3390/molecules23020104.)

**** (Toshiyuki Nakamura, Noriyuki Miyoshi, Takeshi Ishii, Miyu Nishikawa, Shinichi Ikushiro & Tatsuo Watanabe (2016) Activation of transient receptor potential ankyrin 1 by quercetin and its analogs, Bioscience, Biotechnology, and Biochemistry, 80:5, 949-954, DOI: 10.1080/09168451.2015.1132148)

***** Pengbao Shi et al. Foliar applications of iron promote flavonoids accumulation in grape berry of Vitis vinifera cv. Merlot grown in the iron deficiency soil. Food Chemistry
Volume 253, 1 July 2018, Pages 164-170.

****** Wendy V. Parr et al. Perceived minerality in Sauvignon wines: Influence of culture and perception mode. Food Quality and Preference 41 (2015) 121–132.

Sunday, March 4, 2018

Oolong aroma and taste: processing or variety and terroir?

Found a paper comparing five oolongs each from Yunnan and Fujian, and comparing these to samples of Chinese green, black and puer teas.* The focus of the paper was on the oolongs, to determine whether it was Camellia variety and terroir, or the processing that most affected the sensory qualities of the resulting tea.

The Yunnan oolongs were made from Camellia sinensis var. assamica and the Fujian oolongs from Camellia sinensis var. sinensis, all from the spring 2015 harvest. Here's a picture of the teas from the article:

The teas described in the article. The authors noted that the Yunnan oolong was paler than the Fujian oolong, consistent with differences in polyphenol content.

What fascinated me was that the aromas of the two different types of oolongs were very similar and their volatile chemistry (which provides for the teas’ aromas) were virtually identical. The aromas were significantly different from the aromas of the other teas. What these reslts suggest is that it is processing that influences the aromas these teas.

By contrast, the tastes of the two different kinds of oolongs were noticeabley different, with the Yunnan being less sweet and noticeably more bitter than the Fujian teas. 

I’ve graphed the concentratiions of epigallocatechin gallate (EGCG) and total polysaccharides: 

ECGC and polysaccharide content (in
mg/g) of Yunnan and Fujian oolongs. The differences in content are statistically significant.

What you notice is that the Fujian tea has more ECGC—the most bitter compound in an oolong. So why was the Fujian less bitter than the Yunnan? My guess is that the sweetness of the polysaccharides in the Fujian tea inhibits the perception of the bitterness. 

And the other important conclusion from this paper: terroir and/or variety influenced the polysaccharide content of the teas as well as the catechin content. 

Tea leaves produce catechins in response to sunlight—these chemicals act like sunscreen—so environmental conditons can be expected to make a difference in catechin content. In fact one of the consequences of global climate change has been a decrease in spring rains with the development of droughts in both Yunnan and Fujian provinces, a problem for first flush leaves.**

Friend of Pairteas Selena Ahmed and her colleagues have documented the effects of the increase in spring droughts in Yunnan on catechin content and sensory qualties of the region’s teas.*** With drought and increased sun exposure, catechin content of the teas increased over the past several years, and local tea famers have noticed both a decrease in the sensory quality of the teas and a decrease in the price they recieve for their teas.

* Wang Chen, Lv Shidong, Wu Yuanshuang, Gao Xuemei, Li Jiangbing, Zhang Wenrui, Meng Qingxiong. Oolong tea made from tea plants from different locations in Yunnan and Fujian, China showed similar aroma but different taste characteristics.  SpringerPlus (2016) 5:576 DOI10.1186/s40064-016-2229-y.

**Chen Huo-Po, Sun Jian-Qi. Drought Response to Air Temperature Change over China on the Centennial Scale. Atmospheric and Oceanic Science Letters, 8(3): 113-119. 

***Ahmed S, Stepp JR, Orians C, Griffin T, Matyas C, Robbat A, et al. (2014) Effects of Extreme Climate Events on Tea (Camellia sinensis) Functional Quality Validate Indigenous Farmer Knowledge and Sensory Preferences in Tropical China. PLoS ONE 9(10): e109126.'