Thursday, April 5, 2012

Scientific Research I'd Like To See Done on Tea's Caffeine, Vitamin C, etc.

When conducting research on tea in the course of working on RateTea, I'm often surprised at how little basic scientific research there is out there on the chemical components of various types of tea, such as caffeine, vitamin C, theanine, and the various antioxidants.

Former president George W. Bush, pictured above, conducted a Q&A session in 2005, pictured above; this session, which focused on the topic of terrorism, still left me and the rest of the world with many unanswered questions about tea.

For example, when writing the article on the caffeine content of tea, I found only a handful of studies, and these studies did more to break down myths (like the myth about white tea being low in caffeine or black tea being high in caffeine) than they did to establish clear patterns of which teas have more or less caffeine. When working on the article on the vitamin C content of tea, I found even fewer studies. The results for theanine were similar; I found sources establishing that Gyokuro and Anji Bai Cha were high in theanine, but I did not find much in the way of thorough research characterizing which teas are relatively higher and lower, and explaining why this would be the case.

Some questions I'd like to see answered scientifically:

  • Since it is known that green tea contains measurable vitamin C, whereas black tea contains either no vitamin C or only traces, I'd be curious to see if there is any vitamin C in the greenest of oolongs and the greenest of Darjeeling "black" teas, especially first flush. Given that some of these teas are greener in color than some green teas, I suspect many of these teas are as high in vitamin C as some green teas.

  • I'd like to see some work on the levels of various chemicals in whole leaf tea, compared to broken-leaf tea, including the contents of various tea bags containing fannings or dust, and sachets containing whole leaf tea. These sorts of studies would be necessary to definitively answer questions comparing loose-leaf tea to tea bags.

  • I'd like to see more work thoroughly exploring how the chemical components of tea differ from higher grades of tea, which tend to be more expensive, to lower grades of tea.

  • I'd like to see studies that compare the chemical composition of tea to subjective impressions of its taste and other qualities, conducted by panels of experts and everyday tea drinkers, using blind taste tests. This would shed some light into whether or not impressions of freshness and quality correspond well to chemical changes in the tea.

  • It is known that both Vitamin C and other antioxidants in tea tend to break down slowly over time, and that this process is slowed in teas that have been heated (like green tea). I'd be curious for work establishing how fast these chemicals break down, and if substantial breakdown happens before there is a noticeable change in the aroma or flavor of the tea. I'd also be curious to see if white tea would (as I would suspect) initially have a greater vitamin C content than green tea, but that the vitamin C would break down much faster than in green tea.

These are just a few of the questions that come to mind. Some of these would have health implications and would help answer questions about which teas are healthiest. Although I tend to focus primarily on taste, I would like to have a scientifically-valid answer when people ask me questions about which teas are healthiest. Currently, I find myself giving vague answers to these sorts of questions, because there's not enough research for me to give more thorough answers.

Low-hanging fruit?

Some of these questions seem like they'd be relatively inexpensive and straightforward to answer, as they'd just be a question of testing enough samples through fairly routine methods. Given all the highly expensive, specialized scientific work done nowadays, it seems like a lot of these questions would be more fruitful to pursue. I'd like to offer a hint to academic researchers looking for an easy publication that could attract a lot of attention: these topics might offer some low-hanging fruit.

Pictured here are some low-hanging fruit of the Sorbus aucuparia plant (Rowan tree or European Mountain Ash).

It seems silly to invest a lot of money in costly research on tea, such as controlled clinical trials of green tea supplements, when some of the most basic questions about tea's chemical components remain unanswered.

What do you think?

What sorts of scientific work would you like to have done on tea? Do you think the above questions would be interesting? Do you know of some studies that I've missed that would answer some of these questions or add useful conclusions to the pages I maintain?


  1. Hi!
    You might want to check out the caffeine and antioxydant content of different at (

    Also, for analysis of tea chemical and antioxydant content compared to subjective tasting, I found that paper:
    Ahmed S, Unachukwu U, Stepp JR, Peters CM, Long C, Kennelly E (2010) Pu-erh tea tasting in Yunnan, China: correlation of drinkers’ perceptions to phytochemistry. Journal of Ethnopharmacology 132: 176–185.

    1. Thanks, I've updated the article on the caffeine content of tea, and linked to this analysis by the Camellia sinensis tea house, which I found interesting and informative!

  2. Here's a question that's been bugging me: Why can you resteep Chinese black teas, sometimes as many as 4 or 5 times, but no Indian or Ceylon black gives even a remotely drinkable second steep? It makes good Chinese black teas seem like a bargain — and blacks from Assam and Darjeeling seem inferior, since even if they are whole-leaf and high-quality, it doesn't seem to make a difference for resteeping.

    I see you recently added an article to RateTea on multiple infusions, but it doesn't compare black teas. Any ideas?

    1. Hmm...this has not been the case in my observations. Perhaps there has been a trend in this direction, but I can think of tons of examples to the contrary. Perhaps this could be related to the particular companies or sources from which you are getting your teas. For example, I regularly buy from Upton Tea Imports, and I think their strengths lie in Indian black teas.

      I recently tried a very interesting Darjeeling black tea from the Dooars (low-elevation) area, still in the Darjeeling district though, Putharjhora Estate FTGFOP1 Tippy/Cl First Flush Organic, from Upton, that performed extremely well under multiple infusions. I also recently tried a Singbulli Darjeeling from Harney and Sons which performed better under multiple infusions than my average experience with black teas from China. I had a first flush Darjeeling from Makaibari estate sold by Arbor Teas, which I also found to do well under multiple infusions.

      And I've certainly tried my share of Chinese teas that don't do well under multiple infusions.

      But, if there's a trend in this direction (even if I'm thinking up counterexamples to it) there's a plausible explanation I can think up, which is that the Indian teas were developed primarily for British tea culture, which tends not to infuse tea multiple times, in comparison to Chinese tea culture, which tends to do this (even for more casual tea drinking). This could have led to the selection of qualities in the tea (both through cultivar selection and production process) that would infuse very quickly, and be lost after the first infusion. In selective breeding and production of any food product, there is usually a tradeoff between different qualities, and if you're not selecting for a particular quality, it will often be lost as you select for other ones.

      I could add some of this to the article, but it seems a bit speculative and based on my personal opinion. I try to keep the articles on RateTea a little more objective and keep my opinions and speculative explanations over here on this blog. =)

    2. Hmm, I will have to keep experimenting and see if perhaps I jumped to a conclusion too soon. But I do note that I've come across several sellers of Chinese tea who claim 3 to 5 good Western-style infusions for their black teas, like Seven Cups and Verdant Tea (check the brew instructions on these sellers' websites). I don't see anyone selling Indian tea making these claims. Also, the only black teas I've had so far that took well to 3+ infusions were Chinese, "Yunnan Gold" and "Golden Monkey" style specifically.

      I feel the closest I've gotten with Indian black teas was also a Makaibari, in my case their excellent second flush sold by Silver Tips. I found that by shortening the first steep I could get two steeps out of it; but even so, both were somewhat weak in flavor as a result.

      In contrast, the Yunnan Royal Gold I just ran out of :( from Northern Lights Tea would give three great steeps at 212°F, 2:30, 3:30, 4:30, the last as good as the first.

      Do you know an Indian or Ceylon black tea that gives a strong third infusion? Your review of the Putharjhora only mentions two infusions. If we cannot find one that yields three infusions, perhaps your theory about cultivating teas for British use (without resteeps) is correct.

    3. I was able to brew the Putharjhora for many (5+ infusions) by using more leaf, as I would a Pu-erh. I did not mention this in my review because I found I did not enjoy the tea as much this way. When using more leaf and briefer (~1 minute) infusions, the tea changed quite a lot in character from one infusion to the next. I liked brewing the tea in two long infusions because this created more complexity, there was a confluence of the different characteristics of aroma.

      It's a matter of personal taste, largely, I think.

      One Indian company, which has since closed, Fresh Darjeeling Tea, gave brewing instructions for multiple steepings. They sold a lot of white, green, and oolong Darjeelings though...I actually only tried one black tea from them, and it was fairly atypical too.

    4. Hi Scott, I have very limited experience in Indian and Ceylon teas. But I think your question about re-steepability is a good one! Even when we compare different types of Chinese black teas, they yield very different numbers of infusions. I would like to spend some time thinking about it!

  3. I disagree on the amount of tea research out there.

    From what I've seen, there are two major sources constantly pushing out tea research: 1) major international tea companies (e.g. Lipton) and 2) tea research institutes in the various tea growing regions (Taiwan, China, Japan, India).

    The scientists in the former of these publish mostly on the health benefits of tea, but those in the latter publish on a wide range of topics, such as the factors affecting and effects of cultivation, cultivars, processing methods, chemical composition, quality metrics, the particular species of fungi involved in puer production and so on.

    The problem until recently with all the research in this latter group was that most of it was being done in China, Taiwan and Japan. They then published in Chinese and Japanese in their own forums, and not in international science journals in the English we can read. However, I think I've seen a shift happening here particularly since the early 2000's, with more and more research from the east also starting to appear in English language journals.

    For example, here are some article lists pertaining to the themes you've highlighted, coming from research I did into a scientific article I'm currently drafting on the "Factors Affecting the Actual and Perceived Amount of Caffeine in Tea" (interim presentation available here):

    * On the relations between the chemical composition and the (perceived) quality of tea
    * Comparisons of chemical composition between different commercially available teas of various types and qualities in different regions around the world
    * On the effects of processing methods on the chemical composition of tea
    * On the effects of cultivar on the chemical composition of teas
    * On the effects of geography on the chemical composition of teas
    * On the effects of seasons on the chemical composition of teas
    * On the how various infusion parameters affect the composition of the final drink

    1. Thanks, I really don't know what's out there in non-English-language sources, and it seems plausible that there's be a lot of research in China, Taiwan, and Japan that is not translated to English.

      Thanks for these links too.

      I haven't looked through these individual studies, but when doing my research, there were a lot of studies that I found it was hard to draw conclusions from, because they would draw conclusions using averages, but when you examined their data, the samples were too variable from one specific tea to the next to actually say anything about ranking them. Glancing over the abstract of some of these, esp. the effects of various factors on the chemical composition of teas, I'm wondering if these studies are similar. In order to really say that one category is > or < another category in any respect, one needs to have a representative sample of what's out there, and a large enough sample size that you can get statistical significance. That's been missing in every study I have looked at so far.

    2. I think most of the papers listed do test for statistical significance and report on it. The issue may be more of a "type of study" -thing, owing to the fact that the chemical composition of tea is a result of a very complex interaction of factors.

      For example, from the research I've read it seems that cultivar is the single most influential factor in determining caffeine and polyphenol contents of teas. These results seem solid, because across the studies, there are hundreds of samples and repeated tests, and because it has been possible to eliminate the many confounding factors to a great extend: the teas tested generally come from tea germplasm repositories, where the different cultivars have been nurtured and processed in the same way, in the same soil and climate conditions.

      Then, recognizing this, one of the studies on using polyphenols as geographical indicators in Japan was able to rule out the effect of cultivar by making sure each of their samples was of the Yabukita stock.

      Similarly, at least the best study on weather and soil effects in different locations made sure to use same cultivar teas from the same producer with the same care instructions, to try to filter out any potential effects different management would have on the results.

      Now, on the other hand, the studies comparing commercially available teas generally can neither restrict nor expand their sample to cover all combinations, so with them one is stuck with averages. But they're still useful, just answering different questions. For example, based on the research I've read it seems that on average, black teas available in Middle Europe: 1) have more caffeine and EGCG than green teas, 2) Their instructions on average specify usage of more leaves, longer infusion times and more water, 3) The leaves of black teas are more often CTC manufactured and 4) The green teas are more often artificially flavored (=generally of poorer original quality).

      While this doesn't tell us anything about green vs. black or CTC vs orthodox in general, combined with the more isolated factor studies it can give us additional information on the experience of the general population on a more general level with regard to for example experiencing the amount of caffeine in green vs. black tea.

    3. Thanks...I began integrating some of this new info into the article on RateTea on the caffeine content of tea, it's just a beginning...there is still a lot of material I can add to the other articles on the site, and probably more I can add to the caffeine article too.