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.

Tea, Cha, or Chai?

Here is an excerpt from my upcoming book "Tea: a Nerd's Eye View." Victor Mair, whose work is the source for this blogpost, is Professor of Chinese at the University of Pennsylvania. I had the privilege of meeting him first through my brother-in-law, who was his classmate as they were working on their PhDs in Chinese at Harvard, and subsequently at the extraordinary exhibit of the Tarim mummies at the University of Pennsylvania (Here's a Youtube video of his talk about the mummies). Since the publication of his book with Erling Ho, "The True History of Tea," he has been in demand as a speaker at tea events throughout the US, including one at my old academic home, Cornell University, entitled "Tea High and Low: Elixir, Exploitation and Ecology Conference" (October 26 - 27, 2018) where I had the pleasure of meeting him again.

According to sinologist and linguist Victor Mair, as outlined in Appendix C of his book with Erling Ho, “The True History of Tea,” the words used for tea in the world’s languages have followed the paths taken by the leaf itself.

The genetics of the Camellia sinensis plant show that it was first cultivated in areas neighboring the Yun-Gui plateau, while it was used as a wild plant both there and in the corner joining Southwest China, Tibet, India, Bhutan, and Myanmar/Burma.

The languages spoken in the Yun-Gui area belonged to the Austro-Asiatic group, the oldest language group South Asia. These languages appear to have spread south from there along the course of the Lancang/Mekong River, where we find both wild and cultivated Camellia sinensis today. 

Map of the Lancang/Mekong River basin. Grey shows the areas from which the Austr-Asiatic languages spread. The large red dot indicates the general area of the Yun-Gui plateau. The smaller red dot indicates Xishuang-banna on the banks of the Lankang/Mekong River, a center for  puer production—fermented teas were among the first teas exported. The green dot indicates the Southwest China/Tibet/India/Bhutan/Burma-Myanmar corner, where Tibeto-Burman languages are spoken. The dark red arrow points to the Nu/Salween River, and the green arrows to the Irawaddy River. 

Map by Shannon1, provided by Wikipedia under the GNU Free Docu-mentation License Version 1.2. Dots and arrow added.

In the Austro-Asiatic language group the word for a leaf was originally “*la.” (The asterisk indicates a reconstruction.) People speaking Mon-Khmer languages, a language group descended from Austro-Asiatic, settled among the botanic riches along the Irawaddy, Lancang/Mekong and Nu/Salween rivers. “La” became the specific term for Camellia sinsnsis when consumption of the leaf as a fermented salad or chew became an integral part of their culture, and variations on the theme of tea infusions were practiced, probably about 5000 years ago, or possibly earlier. 

Sinetic-language speakers (= people who spoke some form of what was eventually become one or another variant of Chinese) came into contact with the Mon-Khmer people and their tea culture some 3000 years ago, and began the deliberate cultivation of Camellia sinensis in what is now Sichuan. 

The “First Emperor” Qin Shi Huang (also called Shi Huangdi) conquered the people living and growing Camellia sinensis in Sichuan, and, by 221 BCE, brought the practice of drinking tea into Chinese culture. 

Eventually, cultivation spread, to neighboring Fujian in particular where the plant may have hybridized with local wild plants to give the many different leaf forms now seen in Fujian.

In the sinetic Southern Min language of Fujian and Taiwan, “*la” was transformed via “dra”—apparently an old sinetic form—into “te.”

Outside the Southern Min-speaking areas “*la” evolved into “cha,” 

Tea was brought to Korea and Japan via the northern route, so the word in those languages is “cha.” 

The Portuguese were the first to bring tea to Europe and called it “cha,” the pronunciation in Guangdong—they held Macao in that province until 1999. However this pronunciation did not gain traction in the rest of Europe, because the quantities of leaf imported were so small. 

It took the Dutch to bring large quantities of tea to Western Europe in the 17th century. They traded in Amoy (now called Xiamen), in Fujian, as well as in Formosa (now Taiwan) and brought the “te” pronunciation with them to Western Europe.  

“Chai” sounds like a transformation of “cha.” According to Victor Mair, it is indeed a transformation of “cha,” one first created in Persian to become “chay.” People on the land routes through Central and Western Asia to the Middle East and Eastern Europe used Persian as a common language of trade at the time when tea drinking spread to these areas.  

Thus “chai” was brought to India from Central Asia by the Moghuls in the 16th century, then picked up in Hindi-Urdu, and finally it came into English. 

What happened at the Green Tea Processing Workshop at World Tea Expo.

Jason McDonald and Timmy Gipson were responsible for this fascinating 2-day workshop on green tea processing. I take the liberty of saying ”fascinating” even though I wasn’t physically there because it fascinated me from the start of the concept to the finish when I “attended” via iPhone.

The idea behind this workshop was to show how each kill-green process works and what each process brings to the cup. Kill-green is the phrase the Chinese use to describe the processes whereby the enzymes in the leaf are denatured and no longer play a role in the tea’s flavor development.

The Great Mississippi Tea Company's new garden in the mist. It will be ready for harvest in a few years.
As part of the workshop, Jason explained in detail how they go about preparing the soil and growing their plants to yield their exquisite teas.

Timmy and Jason and friends plucked and sorted the leaves from their Great Mississippi Tea Company tea farm just before coming to Vegas. 

Sorting the leaves.

To keep the leaves from jumping the gun and producing and then losing too many delicious stress chemicals before processing in Vegas, the leaves were transported in darkness with ice packs and moisture in a big rucksack.

Most of the leaves made it safely to Vegas, though some were too close to the icepacks and suffered a bit.

Once in Vegas, the leaves were allowed to wither overnight, then Jason and Timmy brought them to the Convention Center, ready to undergo the kill-green processes. 

The leaves in Vegas, ready to be processed. The wok and boiling pot are on the table, along with a big sieve to capture them.

After the kill-green discussed below, it was time for the leaves to be rolled in muslin, then dried. Here you can see the muslin cloths after rolling. The difference on color is quite striking. Normally you would expect the muslins from steaming (on the right) to be very pale, but as you can see they are brown, suggesting over-cooking.

Muslins after rolling.

It is important to note that for each pair of the kill-green processes, one group of people carried out one timing, while another group carried out the other timing. The differences in the flavors of the pairs may therefore not only be the result of timing, but also result of subtle differences in handling of the leaves. 

When it came time to taste the brewed teas, I was invited in by iPhone to share in people’s comments and to ask and answer questions. I took notes and Jason sent me his. The following results are compiled from these two sources.

Witnessing the tasting by iPhone!

What were the results? 

Leaves and liquors from the four processes. Clockwise from top:
Pan-fired: left 5 minutes, right 10 minutes;
Steamed: left 2 minutes, right 45 seconds;
Sous-vide: left 20 minutes, right 10 minutes;
Boiling: left 1 minutes, right 2 minutes.
The photo does not accurately reproduce the colors of the leaves. See below.

1) Pan-firing in Chinese and Korean manner: 

For this process the leaves were tossed in a wok. The advantage of this method is that the tea gains a slightly nutty toasty quality. The disadvantage is that the leaves can burn if you don’t keep tossing them and turning them over completely. 

Tossing leaves in a wok.

One of the most curious results of the pan-fired processing was that the 5 minute firing had more of the toasty quality than did the 10 minute firing, which was judged to be more vegetal and greener, even buttery, though still toasty. The 5 minute was bitter while the 10 minute was sweet. 

As you may be able to see from the picture, the 5 minute was somewhat darker as well, suggesting more oxidation and also more Maillard browning products, which give the toasty quality.

One possible explanation for the unexpected findings may lie in the handling. The 5 minute leaves may simply have gotten too hot.

2) Steaming in the Japanese way:  

Steamed leaves: left 1 minute, right 45 seconds.

Steaming also yielded a paradoxical result, possibly explained by issues with the steamer. It has been suggested that the Las Vegas altitude and lack of humidity might account for the results. However, water turns into vapor at a lower temperature at higher altitude and lower humidity, so the observed burnt quality at 45 seconds would have been less rather than more likely. 

The 45-second steaming gave a darker leaf, with uneven color, as if some of the leaves had been properly steamed and some had become too hot. This problem was confirmed at the tasting, where the 45-second tea was found to be less grassy than expected, and to have black tea notes. At the same time, the 45-second steam also didn’t allow enough time for breakdown of the leaf’s cell walls, so it was harder than the 2-minute to roll.

The 2-minute steaming gave a more classical green tea: lighter, more grassy, more vegetal, bitter and astringent.

3) Blanching in boiling water, as home-growers of tea might do: 

Blanched leaves: left 1 minute; right: 2 minutes.

At 1 minute the tea seemed more like what you would expect a green tea to be. The hairs on the tips remained, the roll was lighter so the cell walls were adequately broken down. The flavor was green and vegetal, somewhat bitter while buttery and light, with slight roastiness suggestive of pan-firing.

Two minutes was perhaps too long for blanching: there was an abundance of yellow stems from overcooking. On the other hand the brewed tea was lightly vegetal and smooth according to some. According to others the brewed tea was bitter with a biting astringency!  Another variable one has to take into account in processing is the difference in taste sensitivity among people, especially when it comes to bitterness and astringency.

4) Sous-vide: 

Sous-vide: left 10 minutes; right 20 minutes.

Sous-vide was the most successful method of the four, as both 10 minute and 20 minute processing yielded pleasant teas. I believe that this method is successful under “amateur” circumstances because it involves the fewest variables. The temperature of the bath is constant, there are fewer chances of one clump of leaves becoming more heated than another, and the vacuum means that oxygenation is stopped the moment all the air is sucked out of the bag.

The 10-minute tea was fluffy, with white tips still in evidence. The “green” aroma chemicals were less developed than were those in the 20-minute tea. The 20 minute tea was more vegetal, with a well-rounded though still bitter and grassy taste, and a dry, slightly buttery after-taste that induced salivation.  

Conclusion

Perhaps the most obvious conclusion from this workshop is that processing leaves for tea is not easy. There are so many variables that come into play, over many of which we have limited control. What would seem to be simple is in fact extraordinarily complicated—as complicated as the chemical processes in the leaf, and as sensitive to growth conditions and handling.

IMPORTANT ===>>>  

Want to learn more?  Jason and Timmy are preparing to host an exclusive limited-attendance tea plucking and processing workshop at The Great Mississippi Tea Company farm this coming September! 

Keep an eye on Facebook for specifics!

How the tea leaf protects itself from too much UV irradiation

One of the burning questions people proposed to me in my survey is: why are mountain-grown teas so often more flavorful than teas grown in the valley?

A tea garden on high altitude slopes in Munnar, Kerala, India, with dramatic clouds in the background.

Photo by Bala Karthikeya Pavan Guda on Unsplash.

Of course there are multiple factors involved in the flavor of mountain-grown teas, including increased drainage of the soils, increased fog, which increases ambient humidity, and an increased chance of experiencing the stress of a cold snap. 

One of the most fascinating set of effects of high altitude is the result of higher levels of UV irradiation from the sun. 

UV light causes the leaf chlorplasts to form carotenes and their derivatives, carotenoids. These chemicals serve multiple functions, among which are:

• Capture of UV light energy to transfer of that energy to chlorophyll for photosynthesis, or to dissipate it as heat;
• Capture of excess hydrogen and reactive oxygen;
• Serve as precursors for a number of useful compounds for the leaf cell, and for aroma compounds in tea.

Capture of UV light energy:

UV light from the sun comes in three different wavelength ranges:

• UV-A, or near UV (315–400 nm)
• UV-B, or middle UV (280–315 nm)
• UV-C, or far UV (180–280 nm)

UV-C is completely absorbed by the atmosphere, while some UV-B and most UV-A gets through. The amount of UV-B that gets through depends on altitude: the higher the altitude the thinner the atmosphere, so plants grown at higher elevations are exposed to more UV-B light. 

Exposure to UV light leads the plant to produce carotenoids. These compounds and their precursors, called carotenes, absorb light at the blue and UV end of the spectrum and reflect light in the orange-red range—this is why carrots are orange to our eyes. By contrast, chlorophyll a, the major form of chlorophyll in tea leaves, absorbs and uses light energy primarily in the orange-red end of the spectrum, and reflects green light, making leaves appear green. (Note that chlorophyll b, which is present in smaller amounts, serves as an accessory energy collector for chlorophyll a. It absorbs light in the blue end of the spectrum, but not efficiently at wavelengths below 400nm; in other words it doesn't absorb much UV light.)

By contrast, carotenoids can capture UV-A light energy relatively efficiently, and to some extent can capture UV-B light successfully as well. Then they transfer the light energy to chlorophyll, or they simply dissipate the energy as heat. Incidentally (or perhaps not so incidentally!), in low light conditions (shade, rain, fog), the leaf makes carotenoids to help the chlorophyll capture more energy.

Capture of excess hydrogen and reactive oxygen:

Carotenoids provide a system for dealing with two problems the leaf encounters: the excess hydrogen (H) produced by photosynthesis; and especially the reactive oxygen (O) that comes from photosynthesis and from UV light damage. 

First, the excess hydrogen ions: more hydrogen ions are produced in photosynthesis than are needed for making the leaf’s building blocks, such as sugars, fatty acids, and amino acids. Some of this hydrogen goes to forming a compound called NADPH. 

Second, both photosynthesis and UVB light produce reactive oxygen, that is, oxygen atoms and oxygen-containing structures that react with other chemical compounds, oxidize them, and destroy them. For example, a reactive oxygen atom can attach itself to a polyunsaturated fatty acid in the cell membrane, in a process called lipid peroxidation. It then can build a bridge attaching the fatty acid to adjacent molecules, so the whole membrane breaks up. Other peroxidation reactions lead to breakup of proteins, RNA, and DNA. 

The carotenoids quickly (in a matter of nanoseconds!) take up the reactive oxygen produced. They hand the reactive oxygen over to enzymes that combine it with the hydrogen from NADPH to form water (H2O). In this way the threat posed by reactive oxygen is reduced, while at the same time, NADP is released ready to take up another hydrogen. Having handed over the oxygen, the carotenoids are ready to take up more reactive oxygen, and the cycle can begin all over again.

Aroma compounds from carotenes and carotenoids

Some of the most delicious aromas in teas are made from carotenes and carotenoids, especially aromas with a floral quality, such as rose, lavender, and violet. 

Tea rose 'Mrs Dudley Cross'. Tea roses got their name because many have an aroma reminiscent of black tea, not surprising considering they share many aroma chemicals!
Photo by Solicitr from Wikipedia.

Carotenoids can also be transformed into safranal—safranal is a color and aroma chemical found in saffron—that gives oolongs a subtle but fascinating flavor. 

Beta-damascenone, a carotene derivative, together with the chemical phenyl acetaldehyde found in tea, can give teas the smell and flavor of honey. 

Last in this list, but by far not the only aroma compound in tea derived from carotenoids, is methyl salicylate. It is derived from abscisic acid, which is formed from the carotenoid zeaxanthin when the leaf is stressed, for example with a cold snap. The leaf transforms abscisic acid into methyl salicylate, with its sweet smell of wintergreen, so delicious and desirable in high altitude Darjeelings.

The buildup of carotenes and carotenoids in tea plant leaves grown at high altitudes gives us one reason for their more delicious teas. There are many more reasons, as you can imagine. I’ll be writing about them all in my upcoming book, “The Science and Pleasures of Tea.” Will keep you posted!