Tea under UV!

On the broadcast of my Twitch.tv/vul100 stream, tea leaves under black light revealed their many hidden beauties. Here are some images taken from that stream.

To highlight what you can see with UV light, here the same Ali Shan leaves under regular and black light:

On the left you can see gradations of green to yellow, but under black light on the right, the same leaves burst with color. Red corresponds to chlorophyll, yellow and green correspond to a number of different compounds, primarily the grassy and jasmine derivatives of membrane fatty acids, but also amino acids, aldehyde compounds with a floral quality such as phenyl acetaldehyde, and the furfurals, such as 5-methyl furfural with its sweet caramel-like aroma. The dark purple corresponds to the larger polyphenols, such as theaflavin and thearubigen, and potentially other compounds that are produced by heating the leaves.

Incidentally (for those of you interested in chemistry), I went through my collection of tea aromas to determine which ones lit up under black light and which ones didn't—in general, alcohols such as the rose-smelling 2-phenyl ethanol and benzyl alcohol did not, while the corresponding aldehydes (phenyl acetaldehyde and benzyl aldehyde) did, with colors under black light being variations on yellow.

Keeping these colors in mind, let's now look at a green tea from The Great Mississippi Tea Company. In the top left image the leaves were heated sous-vide to denature the polyphenol oxidases, and the bottom right image the leaves were pan-fired.

Mississippi Queen green tea sous-vide.

Mississippi Queen green tea pan-fired.

The red color corresponds to chlorophyll and the more purple to the polyphenols. What was perhaps more apparent to the naked eye than in these photos was that the sous-vide retained more of its chlorophyll while the leaves of the pan-fired tea were overall more purple. 

Pan-firing allows oxidation to progress and larger polyphenols to form until all the polyphenol oxidases in all the leaves are denatured. By contrast, sous-vide is carried out in the absence of oxygen, so the polyphenol oxidases can't act even though they denature over time.

(Parenthetically, "polyphenol oxidase" is plural above because the leaves actually have two forms of the enzyme.)



Was entranced by this bud-only yellow tea, also produced by The Great Mississippi Tea Company, called Mississippi Sunshine:

Mississippi Sunshine

The outer wrapping of the buds is red from chlorophyll and purple from the polyphenols, while inside the trichomes are yellow, thanks to the floral compounds as well as amino acids and other flavor compounds offered by these "hairs."

Here is a Bai Mu Dan, showing how a white tea can offer its panoply of flavors. At the top is a leaf that has been mostly oxidized (purple) but with a tuft of yellow-green trichomes coming out of the furled mini-leaves in a bud; below is a young still-curled leaf with abundant chlorophyll and trichomes peeking out, and below that another young unfurling bud. Its greenish yellow color comes from the presence of yellow trichomes against a background of oxidized polyphenols. You may also notice the yellowish "dust"around the leaves—these are shedded trichomes.

Oolongs also offer fascinating images and insights into their composition under black light. Below right is a lightly oxidized pouchong and and a highly oxidized Da Hong Pao:

Pouchong

The pouchong has a lot of leaves with chlorophyll and greenish leaves from the presence of trichomes against a background of red and purple.

Da Hong Pao

Da Hong Pao has much more purple, showing its highly level of oxidation. In fact it is not much different from the black teas below.




Here is a Dian Hong black tea. This tea has "golden tips"—in other words, buds. In the photo below you can see that the leaves are mostly purple from the polyphenols, but there is still some chlorophyll present. The oval indicates a bud. It is not as bright a yellow as the buds shown above, because its catechins (which are abundant in buds) have been oxidized into polyphenols, but there are still some of the floral compounds that fluoresce yellow present, giving the bud a slightly orangey color.

Dian Hong, bud circled.

Black Magnolia

And above is Black Magnolia, again from The Great Mississippi Tea Company. It has been more extensively oxidized than the Dian Hong, so most of the leaves are a rich dark blue-purple. Still there is at least one leaf that has retained some of its chlorophyll. At the same time, there are a couple of very young leaves that are blue-green—they have an abundance of trichomes, so the overall color is a combination of yellow and blue purple, in other words blue-green. 

This post represents just a short line-up of black light images of teas, but you can already see that one can glean a lot of information about a tea and its qualities using black light. Enjoy!

===>>> Available on Amazon: Tea: a Nerd's Eye View by Virginia Utermohlen Lovelace MD

Going live on twitch.tv/vul100!!! Here are some answers to FAQ's

On February 5th 2020 I'll be going live on twitch.tv/vul100!  Here are answers to questions you may have:

What is twitch.tv?

— Twitch.tv is a service for live streaming. Live streaming is a way of broadcasting live video over the internet, and of recording the broadcast so that people can watch later. You will be able to watch my channel by going to twitch.tv/vul100.

What will you do on twitch.tv/vul100?

—I’ll be talking, demonstrating, carrying out experiments, interviewing, and best of all, chatting with you. 

It’ll mostly be about tea, but we can chat about coffee, wine, beer, and food, and all manner of things that have caught our attention. 

What will I see when I go to twitch.tv/vul100?

—Here's how the screen is laid out and what you can do:

When will you be broadcasting on twitch.tv/vul100?

—Monday and Wednesday at 9pm Eastern Standard Time US, starting Wednesday February 5th.

How long will the broadcasts last?

—About an hour…depends on what we do and what questions you have.

Do I need anything special to watch twitch.tv/vul100?

— You can watch twitch.tv/vul100 on any platform and device that has access to the internet.

If you want to chat, though, you need to sign up.

How do I sign up?

Go to https://www.twitch.tv and select the "Sign up" button on the top-right portion of the page. This will open the Log In / Sign Up screen. To sign up for a new account on Twitch, fill out the “Sign Up” form. 

When you sign up you choose a nickname that you will use for chatting—and you will also be able to create your own twitch channel using the nickname! 

Why vul100 and not pairteas?

—vul100 is the nickname I chose when I first signed up for twitch.tv so I could watch my daughter and other friends. 

Can I support twitch.tv/vul100?

—Yes!  The key is to become a follower—then you will receive a link via email for joining the broadcast each time I go live.

Further, Twitch.tv allows you to become a subscriber for a small fee of each month. As a subscriber, you will be able to ditch the pesky ads that play whenever you sign in to a live broadcast—it’s these ads that support the twitch.tv infrastructure. By subscribing you will continue supporting the infrastructure while it may also give me a small amount to support tea purchases and tea-related charities, etc. To find out more, go to:

https://help.twitch.tv/s/article/how-to-subscribe?language=en_US 

===>>> So eager to get together with you on twitch.tv/vul100! <<<===

“The Aromas of Wine and Tea: a Sensory Adventure!” at the Global Tea Initiative, January 17 2020.

Note: all photos in this post are courtesy of Yan Chen, Yan Chen, Professor, Louisiana State University Agricultural Center Hammond Research Station.

Such fun to give the talk “The Aromas of Wine and Tea: a Sensory Adventure!”  with the help of Marzi Pecen. Here we are talking with attendees before the start—Marzi is standing on the right:

In the Sensory Theater of the Robert Mondavi Institute for Wine and Food Science we could have a true sensory adventure—we could experience directly how the aromas of wine and tea shift and change as we alternatively sniffed individual chemicals and the teas and wines.

Here’s a picture of the set-up:

In front of each participant were six cups (the wine glasses in the back were in place for Andrew Waterhouse’s talk about wine aging, that followed my talk). 

The three cups in front held (left to right) a green, oolong, and black tea, all Ready-to-Drink from Ito-En—thank you so much Rona Tison of Ito-En for providing these. The three cups behind the tea cups held a Chardonnay, a Pinto Noir, and a Cabernet Sauvignon, all from Robert Mondavi — many thanks to Babette Orendain of the Institute for the wines, and to her and her UC Davis student helpers for setting out everything!

(fBTW, the green tea was very close in color to the oolong—it was pan-fired—but it was clearly green tea by its aroma).

Earlier in the day, Colloquium speaker Susan Eberle, Professor (Chemist) of Viticulture and Enology, and Associate Dean, Undergraduate Academic Programs, College of Agricultural and Environmental Sciences at University of California Davis, had described some of the aroma chemicals common to tea and wine. Here is a picture of one of her slides:

To my great delight, I had chosen compounds that corresponded to these categories for my demonstration. I was planning to touch on all of these categories, but time was running short (we had to start late) so I chose just three:

• 2-phenylethanol, a phenylpropanoid, 
• β-damascenone, a C13-norisoprenoid,
• vanillin—note that vanillin is developed during the heating steps in tea and comes from the oak barrels for wine., so is not actually either in the grape or the fresh leaf to any extent.

We started by soaking perfume blotter paddles ("touches") then sniffing 2-phenylethanol and β-damascenone separately and then together. When we sniff them together our olfactory bulb joins them together as "odor objects" different from the two separate smells. For me and for many of the participants, the resulting odor object was "honey." However, people differ genetically in their ability to smell β-damascenone, so the "honey" effect was less pronounced for some. This observation allowed for a very short comment on the genetic ability to smell different aromas in teas and wines.

The next effect we experienced was masking. People first sniffed the Cabernet Sauvignon, then sniffed the 2-phenylethanol or the β-damascenone, then sniffed the wine again—the smell of the wine disappeared! The same held for the black tea. Neither the wine nor the tea has a significant amount of these compounds so, at the concentrations on the perfume paddles, these chemicals effectively masked the other aromas in the tea and wine.

By contrast, when we carried out the same experiment with the Pinot Noir and the Oolong, the aromas of each became richer and even more pleasant. This wine and this tea both have significant amounts of these chemicals; sniffing the paddles before sniffing the wine and tea brought out their aromas—an additive effect.

Vanillin is produced when oak barrels are fired, so oaked wines will have a lot of vanillin. The Chardonnay we had was only lightly oaked, so when sniffed alone if had a more fruity, less Chardonnay-like aroma that wasn't as pleasant as that of a more oaked wine would be—Andrew Waterhouse (Director of the Mondavi Institute) and I agreed that the wine had probably been treated with oak chips rather than been aged in a barrel. When you sniffed the wine after sniffing the vanillin, the aroma of the wine improved dramatically. 

Black tea is heated and fully oxidized, so it too contains significant quantities of vanillin, from the breakdown of lignin in the leaf's veins. Just as we experienced with the Chardonnay, the aroma of the black tea became richer after we had sniffed the vanillin. Interestingly, the vanillin somehow incorporated itself into the overall tea aroma, rather than stand out as separate but compatible as it did with the Chardonnay—with the black tea we were again experiencing odor object formation, which could be described simply as "black tea."

By contrast none of these compounds are present in green tea, so sniffing them before sniffing the green tea made the green tea either smell awful (for me) or just loose character completely (for some other people).

BTW, you can carry out some of these experiments at home with household herbs and spices. Will be live streaming to show how these experiments work on my upcoming twitch.tv channel. Details and link to come!

Or you could get samples of the actual chemicals in a Scents of Tea kit at http://scentsoftea.com and carry out the experiments with all manner of scents, wines, and teas.

==>> Now available on Amazon: Tea: a Nerd's Eye View.

5th Annual Colloquium of The Global Tea Initiative at UC Davis

Such fun at the 5th Annual Colloquium of the Global Tea Initiative—“Tea & Wine - The Great Debate”—at UC Davis under the leadership of Katharine Burnett!

Some highlights:

• People who know me know that I am not really fond of puer…but I was entranced by the dialog between Roy Fong of The Imperial Tea Court in San Francisco (https://www.imperialtea.com/Default.asp), and James Norwood Pratt, tea writer and connoisseur (https://jamesnorwoodpratt.com). Norwood asked the questions and Roy answered, all about how Roy produces his puers in his warehouse in San Francisco. He imports his raw maocha from China, then with a practiced eye for temperature and humidity at different levels in his warehouse, he moves his bings around to perfect them, for years and more years. It was an extraordinarily warm and friendly conversation that highlighted the cordiality that I find so refreshing in “tea people.” Am looking forward to a possible video of another dialog between these two, that my friend Marzi Pecen hopes to get off the ground.

• One persistent theme of the Colloquium was climate change and its effects on both wine and tea. The point about tea was forcefully brought out by Fitrio Ashardiono, Ph.D., Senior Researcher, Asia- Japan Research Institute, Ritsumeikan University, and UCD Visiting Scholar. His talk was entitled Tea Cultivation and Terroir Framework: Developing the Terroir Concept for the Tea Industry, but really focussed on how climate change would affect tea growing in Uji Japan—the home of exquisite matcha—and what structural issues would affect the growers’ responses.  It’s clear that the problems will be difficult to solve, but equally clear that we must solve them. (It was in the 70’s in Boston in January, only a few days earlier!)

Fitrio displayed a picture similar to this one, showing that tea growing in Uji occurs in the middle  of an urban environment, complicating the conditions for growing tea.
Photo by Arboramo, Wikipedia CC BY-SA 4.0.

• Of course, UC Davis is famed for its Viticulture & Enology Program, so we were guaranteed some super interesting information about wines. In particular, learned from Ron Runnebaum, Assistant Professor, Viticulture and Enology, UC Davis, about one of my favorite wines, Pinot Noir, and the effects of growing the wine in different places on the West Coast. Thoroughly nerded out on all the graphs and Principle Component Analyses—when I was at Cornell, had huge discussions with my graduate students about how to analyze our data—do you use Principle Component Analysis or Factor Analysis or neither? And how do you interpret the results?  Was thrilled to see some of my favorite tea scents mentioned on the graphs—scents that I used in my talk.

Day 2 was Sensory Day, introduced by Andrew L. Waterhouse, Director of the Robert Mondavi Institute of Wine and Food Science. Was especially glad to have met him—so very much appreciated his kindness as well as his knowledge.  

• Al Robbat, Director/Professor Chemistry Department Sensory and Science Center and Center for Field Analytical Studies & Technology at Tufts, and inventor of the most complex and effective systems for analyzing aroma chemicals ever, again brought home the effects of climate change on tea and tea quality. With his systems, you can clearly see what changes in monsoon patterns, for example, cause in tea chemistry. Have to look more deeply into this question for another blog post!

• So grateful to Sue Ebeler, Professor, Viticulture and Enology and Associate Dean, Undergraduate Academic Programs, College of Agricultural and Environmental Science at UC Davis, who provided a superb introduction for my experiential adventure that was to come later in the afternoon—she described many of the aromas I was planning to provide, and where they come from in wine and tea. 
• Nikolai Kuhnert, Professor Analytical Chemistry Jacobs University Bremen, Germany also had me nerding out with his talk about tannins entitled High Resolution Analysis of Black Tea and Wine. Nikolai was another of the kind thoughtful people I met at the conference—I can’t say it enough, the people at the Colloquium were people I am proud to be among.
• And Jonathan Cave, Treasury Wine Estates (https://www.tweglobal.com), who talked about tannins in wine, and reminded me of how anthocyanins alter the flavor profile of wines enough so that when added to white wine, people may become confused and think it might be red.
• Then it was my turn. I was fortunate to be able to give my talk at the Robert Mondavi Institute Sensory Theater, where people sat at desks in an amphitheater, with wines and teas arrayed in front of them. Rona Tison of Ito-En (https://itoen.com) provided three ready-to-drink teas, green, oolong, and black, and Mondavi provided a Chardonnay, a Pinot Noir, and a Cabernet. With the expert assistance of my friend Marzi Pecen (she is not only a tea specialist, but a parfumeuse) we handed out paddles/touches with scents on them, and had fun making the aromas of the teas and wines disappear and reappear. More about how this works in my next blogpost.
• Finally, after me came Andrew Waterhouse, with three Cabernet Sauvignons that were so different it boggled the mind. Three different ages, three completely different flavor profiles. Andy talked about what aging does to wine profiles, and neatly summed up what we had heard throughout the colloquium: sensory matters!

One more experience, so exquisite!  Susumu Yotsukawa, designer, www.kisendo.net, brought a collection of wine/sake and tea items to savor with our eyes. Here's one:

A sake cup designed by Susumu Yotsukawa, made of Japanese cherry birch and brass,​ available at https://www.woahjapan.com/product.asp?shocd=WJC00329

Go to the Kisendo website—www.kisendo.net—for more on which to feast your eyes!

==>> Available on Amazon in paperback, my latest book, "Tea: a Nerd's Eye View."

Tea serving temperature

Yet another except from my upcoming book: Tea: a Nerd's Eye View.

Tea serving temperature

Fun question: at what temperature to serve tea? 

The first systematic study I found to answer this question was provided by Ragita Pramudya and Han-Seok Seo, which studied liking and emotional response to coffee and green tea.*

They used bagged pan-fired Korean green tea which can be expected to have a roasted flavor. They prepared the tea by brewing the bags with boiling water for 5 minutes. Under these conditions they had a greater chance of leaching out indole with its animalic quality, and catechins, with their bitterness. They then served the tea at 5ºC/41ºF, 25ºC/77ºF, and 65ºC/149ºF. I’ve graphed their results for the proportion of participants attributing each quality to the teas here:

As you can see, more people assigned potentially unpleasant qualities to the tea served at 5ºC than to the tea served at 65ºC, and more people assigned positive qualities to the tea served at 65ºG than at 5ºC. The tea served at (more or less) room temperature had intermediate qualities. 

Pungency is the term used to describe the sensations induced by activation of the cold trigeminal receptor TRPA1. Catechins also activate cool/cold receptors, so serving green tea at a cold temperature may bring out their bitterness. That's because the trigeminal system serves as a volume dial, so that when there is congruence between the actual and perceived temperature of a compound, the flavor of that compound is amplified.

Type II taste bud cells responsive to sweet use TRPM5, a warm receptor, in their response pathway. In fact you can simply apply mild heat to the tongue, and many if not most people will interpret the sensation as “sweet.” That is why the warmer tea is sweeter, even when no sweetener has been added to it. It is also milder because the bitterness and pungency are dialed down.

Remember how I mentioned that color and flavor can be related? In this same study they asked participants about the color of the green tea, which in fact was a yellow. More participants saw a brown color in the tea when it was hot than when it was cold, and virtually none saw a green color in the hotter brew. 

In the emotional realm, the warmer tea was associated with positive emotional feelings and the colder teas with more negative feelings.

One more important conclusion of the study to include here: “Since females could better detect sample temperature-induced changes in sensory attributes than males, sensory attributes might contribute to likings of coffee and green tea samples among female participants, but not [as strongly] among male participants.”

In the US, and especially in the South, there is a strong tradition of consuming sweetened iced tea. The sweetness added to the tea counteracts the bitterness and astringency of the cold tea. An open question is whether sweetness can also add to the emotional positivity of the person drinking it!

*()*()*()*()*()*()*

To preorder "Tea: a Nerd's Eye View" go to 

https://checkout.square.site/buy/TNAGNP3N4YZX6USMEZCSMDB4 

Be sure to check out the "Variation" for the pre-order price.

The book should be completed in the next couple of weeks!

* Ragita C. Pramudya & Han-Seok Seo. 2018. Influences of product temperature on Emotional Responses to, and Sensory Attributes of, Coffee and Green Tea Beverages." Frontiers in Psychology, Gale Academic Onefile, https://link.gale.com/apps/doc/A522502274/AONE?u=nysl_sc_cornl&sid=AONE&xid=9c9e7154. Accessed 7 Sept. 2019.

The shape of your tea cup and the flavors of your tea

Another excerpt from my upcoming book "Tea: a Nerd's Eye View:"

Tea is served in glasses, bowls, and cups that come in a multitude of shapes and sizes, made from an amazing array of materials. 

The effects of these different containers has not, to my knowledge, been explored in a systematic and scientific way, where (for example) shape is matched to the qualities of a tea. 

However, there is a growing body of evidence that the shape of a glass influences the aroma  of wine as you drink it. A tulip shape seems to do best for all types of wine. *

The tulip shape allows more aroma volatiles to escape from the surface of the wine; then it concentrates them at the opening at the top of the glass. Thus for wine, one of the important parameters for aroma is the ratio of the opening of the glass (top arrow) to the maximum diameter of the glass (bottom arrow). I was interested to note that the sulfur dioxide diminishes as the ratio goes down, suggesting that this gas is less likely to escape the more tulip-like glass.

A similar result was found for coffee: aromas were more intense when the coffee was served in a cup with a tulip shape, and sweeter when sipped from a cup with a wide opening. Whether these results were the consequence of expectations is open to question—in an online survey of coffee cup shape, respondents maintained that mugs with a narrow opening would be more aromatic, while short mugs with a wide opening would be sweeter.**

Nevertheless, ceramicist Peter Ting has offered a set of three porcelain cups, designed to bring out dfferent aspects of a tea: a “fragrance” cup, a straight sided cup, and a cup with a slightly flared lip.*** 

Towards the end of an extensive podcast on teaware, Kevin Gascoyne shared a tasting experience with host Ken Cohen, sipping a Bai Ruo Xiang Rock Tea from Wuyi from each of Peter Ting’s cups.****

The following table gives the results:

	Fragrance cup	Straight-sided cup	Flared lip cup
First sips, hot tea	Most aromatic, full, complex	Lighter, less flavorful compared to fragrance cup	Less complexity than with fragrance cup, but more “minerality.”
Cooled down	Same	More fruity and “darker” than at first	More complex than first sip, notable minerality

Ting’s fragrance cup is tulip-shaped with a slight flare at the top—the same principle applies here as it does with the tulip-shaped wine glass: aroma volatiles accumulate in the headspace of the cup and then funnels them to your nose and mouth. This cup was designed especially to take advantage of the aromatics in oolongs—this Rock Tea benefitted from this cup.

The straight-sided cup didn’t do justice to the tea. Ting and colleagues found that a straight-sided cup was best for black teas. Black teas, and especially teas made from assamica leaves, tend to be brisk, which is another way of saying that they activate both TRPA1 and TRPV1 receptors on the trigeminal nerve. The straight-sided cup delivers the tea further back in the mouth, where there are more of these receptors, especially TRPV1, so you can expect greater briskness. 

The Wu Yi Rock Tea served by Kevin Gascoyne in this trial lacks many of the TRPV1 activating chemicals, so the “brisk” effect is absent, while the shape of the cup allows the aromatic compounds to escape before you sip, rendering the tea less flavorful. 

As the tea cools down in the cup, however, the warm cool/cold reeptors of the trigeminal nerve are less inhibited by the hot temperature of the tea. The fruity compounds that activate TRPV3, the warm receptor, and TRPM8, the cool receptor, are no longer suppressed, so these flavors can be appreciated—remember, trigeminal activation serves as a volume dial, and trigeminal receptors usually inhibit each other. The one exception: under certain conditions, TRPV! and TRPA1 can mutually enhance, giving the brisk sensation.

Finally, the cup with the slightly flared lip was designed for green tea. The slight flare delivers a wider flood of tea into the mouth, activating more taste buds in the front and sides of the tongue, and fewer in the back. There are proportionally more bitter receptors in the back of the tongue than in the front: this delivery gives the sweeter elements of a green tea a better chance to dampen the  bitterness.  

It’s interesting to note that the flared lip cup yielded a greater sensation of minerality from the Rock Tea. This sensation probably comes from activation of the trigeminal receptor TRPA1. When less fragrance from the tea reaches the nose as you sip, the trigeminal effects in the mouth and throat can become more prominent. As the tea cools down, the ability of TRPA1 to respond increases (it's the cold receptor), so sensations of minerality increase.

All in all, the shape of your cup matters!

* Francesca Venturi, Gianpaolo Andrich, Chiara Sanmartin, Isabella Taglieri, Giancarlo Scalabrelli, Giuseppe Ferroni & Angela Zinnai (2016) Glass and wine: a good example of the deep relationship between drinkware and beverage, Journal of Wine Research, 27:2, 153-171, DOI: 10.1080/09571264.2016.1160879 

** George Van Doorn, Andy Woods, Carmel A. Levitan, Xiaoang Wan, Carlos Velasco, Cesar Bernal-Torres, Charles Spence,Does the shape of a cup influence coffee taste expectations? A cross-cultural, online study. Food Quality and Preference, Volume 56, Part A, 2017, Pages 201-211. https://doi.org/10.1016/j.foodqual.2016.10.013.

*** You can find more about these cups , including pictures, at https://peterting.com/branding. 

*** https://talkingteapodcasts.com/2019/02/01/choosing-teaware-for-flavor-aroma-and-experience/ accessed September 2, 2019.

Classical Chinese poetry and the aftertastes of oolongs

Another excerpt from my upcoming book, "Tea: A Nerd's Eye View:"

You may see Tie Guan Yin tea advertised as having a “Yin Yun” or “Yin Rhyme” aftertaste, and Wuyi rock teas as having a quality called “Yan Yun.” “Yun” in this context means “rhyme.” 

What would a rhyme have to do with a tea’s aftertaste?

With respect to rock teas, “Yan” can mean “rock,” but it also refers to the “male” principle—saying that rock tea has “Yan” is really a pun.

To understand the many layers of this play on words, it is important to know that Chinese singing and by extension Chinese poetry have a Yan (masculine) and Yin (feminine) rhyme system.

This system differs from the rhyme systems in English, though we have some of the same underlying concepts of masculine and feminine. In English we speak of masculine rhymes as consisting of one syllable, and feminine rhymes as consisting of two or more syllables. The English masculine rhyme can be abrupt and in your face, while the feminine rhyme is more supple and musical. The Chinese masculine and feminine rhymes have similar qualities.

As Ray Wen Wei states:

“Shih is a modem style of poetry (''jin ti shi") matured during the early Tang [618-690 CE]. It constrains a poem to eight lines of five or seven syllables each. With a single rhyme [system] running through it, the poem is divided into four pairs, namely "start­ing," "extending," "turning," and "completing," respective­ly. These appear in the western classical sonata form of music in the same order, as the "theme," "development," "transi­tion," and "recapitulation." The rhyme used throughout the poem is chosen from one of two divisions of the vowel sounds. In general, these are divided as either long, bright sounds (called "yang" rhyme) or short, dim sounds (called "yin" rhyme). The choice of this rhyme determines the mood of the poem, similar to the choice of a major or a minor key in music.” *

The Yan Yun "masculine" aftertaste of, say, a Ruo Gui rock tea, classically lingers for a long time. It gives you the clear bright impression you would expect from activation of TRPA1, the trigeminal cold receptors in the throat.

By contrast, Tie Guan Yin gives a sweet, gentle, more muted after-taste—breathy rather than clear—the quality that Pulleybank and his colleague ascribe  to the Yin speech tones in Chinese.**

Here is a Chinese poem about tea, with translation and important-to-read notes at http://chadao.blogspot.com/2009/04/song-dynasty-tea-poem-zhu-xis-tea-stove.html

茶灶 朱熹 CháZào -- Zhū Xī (1130-1200 CE)

仙翁遺石灶 xiānwēng yíshízào宛在水中央 wǎnzài shuǐzhōngyāng飲罷方舟去 yǐnbà fāngzhōuqù茶煙裊細香 cháyān niǎoxìxiāng 

'Tea Stove' by Zhu Xi 

Stone stove left behind by immortals,Lies crooked in the center of the stream.
Tea finished, two boats drift on abreast,Tea smoke; wafting delicate fragrance.

The "grave accent" in pinyin indicates the short breathy falling tones of a "Yin" rhyme...

...and here is a photo of the Nine-Bend River in Wuyi, the location of the poem, by Zhangzhugang, Wikipedia,  CC BY-SA 3.0 license.

(Incidentally, notice the orange-red color of the Wuyi rocks. It comes from the presence of iron. Excess iron causes tea plants to produce kaempferol, a flavonoid that binds up the iron so it doesn't damage the plant. In your mouth  kaempferol activates TRPA1—the cause of the Yan Yun effect of Wuyi rock tea.)

* Ray Wen Wei . Chinese classical poetry is based on universal principles of singing.  EIR Volume 19, Number 13, March 27, 1992.

**E. G. Pulleybank and 蒲立本. “The nature of the middle Chinese tones and their development to early Mandarin/中古汉语声调的本质和到早期官话的演变. Journal of Chinese Linguistics, vol. 6, no. 2, 1978, pp. 173–203. JSTOR, www.jstor.org/stable/23752830.