The following are two sample articles. The first is an article covering caffeine in tea, the other describing a specific tea. The current versions of these articles can be found at Dong Ding (wulong tea) and Caffeine in Tea. References are shown in the full article. Sign up for a Tea Geek Membership to gain access to all of the articles!
Caffeine in Tea
Caffeine is perhaps the most well-known chemical component of tea. Whether it's reviled or revered, caffeine inspires more strong opinions and beliefs than any other tea component. But how much caffeine is there, really, in your cup? That's no easy question to answer.
Looking at the dry leaf, the variation in a black tea can be immense. By dry weight, caffeine can make up as much as 6% of the leaf, to as little as below 1%.
Many factors influence caffeine levels in any given cup of tea. First, the varietal of the tea plant makes a difference--Camellia sinensis var. assamica (the "India varietal") produces as much as 33% more caffeine than Camellia sinensis var. sinensis (the "China varietal"). This difference may explain the perception and claims that green tea (usually made from China varietals) has lower caffeine than black tea (usually made from India varietals).
Other differences include which leaves are picked--generally, younger leaves contain more caffeine than older leaves; the fourth has roughly a third less caffeine than the youngest first leaf. Oxidation levels may influence the level of caffeine, but oxidation isn't something that is easily measured scientifically, making it difficult to determine variations caused by that factor alone. Also, plants that were propagated by seed produce more caffeine that plants propagated by cutting or other cloning methods. Plants fed with nitrogen fertilizer produce more caffeine than those that aren't, or that are grown in low-nitrogen soil.
Another variation comes based on when the tea was picked. For example, in Kenya, summer-picked teas have lower levels than winter-picked. Sometimes the seasonal difference is more than 50%, depending on speed of plant growth. And after the leaves are picked, the temperature and length of time they are withered before final processing slightly affects caffeine levels, as does other aspects of processing like drying. And whole-leaf teas seem to release different amounts than broken leaf like you might find in a tea bag.
In addition, what technique was used to brew the tea and what temperature of water is used affect how much caffeine makes it from the leaf into the cup. You sometimes hear that tea can be decaffeinated by giving the leaves a quick brew which you discard, then brew again. However, research has shown that only about two-thirds of the caffeine comes out in the first five minutes of brewing. This means that a second brew will generally be lower in caffeine than the first, but it would be incorrect to call it "decaffeinated," especially if the first brew is shorter than five minutes.
The upshot of all of this is actually rather simple--it's almost impossible to know accurately how much caffeine is in your cup. And if you see statistics about caffeine levels that don't tell you the varietal, propagation method, which leaves were picked, how long they were withered, harvesting season, and leaf grade, then the results need to be taken with the proverbial grain of salt.
The good news, however, is that the highest levels measured in most teas tend to be about half that of coffee--less than 100mg per cup of tea. Luckily, the negative effects of caffeine tend to start showing up at the 300-500mg per day level, and then generally among sensitive groups such as pregnant women with risk factors for miscarriage. For most people, then, two or three cups of tea a day is seen as a safe level for all but the most sensitive, assuming no other sources of caffeine like cola or coffee. (Of course, everyone is different, so consult health care professionals for recommendations specific to your situation and health conditions.)
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Dong Ding (Chinese: 凍頂; Hanyu pinyin: dòng dǐng; lit. "frozen summit" or "frozen peak") is a wulong tea, from Lugu village on Dong Ding Mountain, Taiwan. Many teas are now called "Dong Ding" that were not made on the original mountain but are made after the style of these teas. Like several other notable Taiwan wulongs such as Tie Guan Yin and Baozhong, Dong Ding is often aged. Aged versions of the tea are often re-roasted every year or two, meaning many different levels of roast are available based on the original processing and the tea's age.
- Family: Wulong
- Cultivars Used: Qingxin, Ruanzhi, Jinxuan, and Cuiyu are popular; the first cultivar used in the Dong Ding Shan area was Shicha but it is rarely used now
- Oxidation: Varies on who you ask--15%-25%  to 30%-40% to 40%-50%  to 80%
- Roast: Varies, but traditional Dong Ding is lightly roasted
- Production Area: Originally only Lugu village on Dong Ding Shan, Lugu Township, Nantou County, Taiwan. Now many mountains in both China and Taiwan produce a similar style.
- Other names: Frozen Summit, Icy Peak, Tung Ting
Plant and Production
According to the three tea farmers of the Su family (4th and 5th generation tea makers) interviewed by Tea Geek founder, Michael Coffey, batch sizes depend on number of pickers available but generally fall in the 700-800 jin range (420 to 480 kilograms, or 926 to 1058 pounds). The raw leaf is sun withered for as little as 20 minutes if the sun is strong, or as much as 3 hours if the weather is cloudy. Overcast skies are preferred for this stage because bitterness can result if water is driven out of the leaf too quickly, or if too much water remains in the leaf when it is moved on to the next stage.
Next, the leaves are brought indoors to wither for an additional 7 to 8 hours. They are then tumbled for as little as a few minutes or as much as an hour or more. The leaves are then put on round bamboo mats to oxidize for 2.5 to 4 hours. Each mat holds roughly 7 to 9 jin each.
Finally, the leaves are quickly heated in a step called "killing green" which stops oxidation, then rolled into balls and dried. Some consider 12 hours to be the "perfect" duration between the picking and the killing-green stage. This timing would only happen when the weather does just what the farmer wants for the more atmospherically-sensitive stages of processing.
The tea can be sold at this point as a "green wulong" (especially if it has been more lightly oxidized), or it can be roasted. Older, more traditional teas were roasted more for a bold flavor. Teas made more recently in Dong Ding are lighter in roast as Taiwan tea drinkers have tended to increasingly value fragrance relative to flavor or mouth feel. The older teas were baked in a charcoal roaster for 30 to 40 hours for truly artisan or competition quality. With the shift in the market towards fragrance, it is far more economical to roast the teas in an electric oven, resulting in a different flavor profile. A light roast might be done at 80°C, a medium roast at 110°C, and a heavy roast up to 150°C. Length of time in the roaster would depend on the moisture content of the tea, the ambient air, and the desired end product, and balancing these factors is part of the roaster's skill in making the tea.
Dry Leaf: Rolled pellets ranging from jade green (more lightly oxidized and unroasted) to a deep mahogany brown (more oxidation and/or roast).
Liquor: Clear, golden straw- or honey-yellow for the traditional roasted style; more modern styles produce a lighter and somewhat greener liquor.
Infusion: Skillfully made Dong Dings reveal two leaves and a bud attached to a short stem in most pellets; lower qualities may have single whole or broken leaves. Color, like in the dry leaf, will depend on roast and oxidation levels. Leaves are fairly mature, demonstrated by their tough texture in the infusion.
Scent and Flavor Profile
Dong Ding can have a wide range of flavors depending on level of oxidation and roast, but tends to be known for having honey-like or buttery flavors. Fruity (blackberry or fruit pie) flavors come out with increased aging, roasting, or oxidation.
Pairings and Culinary Uses
Dong Ding wulong tea goes well with milky desserts or dried fruit.
History and LegendThe first tea plants were brought to the Dong Ding Shan area in the 19th Century. Some claim it was early in the century; others claim it was in 1885. Most sources agree that the plants were brought from Fujian province, China.
- ^ a b c d e f Posting of Nigel to Usenet Newsgroup rec.food.drink.tea (8 Jan 2008 01:04:11 -0800).
- ^ a b c d e Caffeine in Tea vs. Steeping Time retrieved 8 Jan 2008.
- ^ Yang DJ, Hwang LS, and Lin JT. 2007. Effects of different steeping methods and storage on caffeine, catechins and gallic acid in bag tea infusions. Journal Of Chromatography. 1156:312-20.
- ^ Posting of Nigel to Usenet Newsgroup rec.food.drink.tea (10 Dec 2007 07:53:58 -0800). This post references two studies. The first is "Tea preparation and its influence on methylxanthine concentration" by Monique Hicks, Peggy Hsieh and Leonard Bell. It was published in Food Research International vol 29, Nos 3-4, pp.325-330. The second is "Tea and the rate of its infusion" from Chemistry in New Zealand, 1981, pp.172-174.
- ^ a b c d e f g h Su Family tour of Dong Ding, Taiwan, tea fields and conversation with Michael J. Coffey, 10 December 2008
- ^ a b c d e Delmas, Francois-Xavier; Minet, Mathias; Barbaste, Christine (2008), The Tea Drinker's Handbook, New York: Abbeville Press, p. 186, ISBN 978-0-7892-0988-7
- ^ a b Gautier, Lydia (2006), Tea: Aromas and flavors around the world, San Francisco: Chronicle Books, p. 141, ISBN 978-0-8118-5682-9
- ^ a b Heiss, Mary Lou; Heiss, Robert J. (2007), The Story of Tea: a cultural history and drinking guide, Berkeley: Ten Speed Press, p. 217, ISBN 978-1-58008-745-2
- ^ Heiss, Mary Lou; Heiss, Robert J. (2007), The Story of Tea: a cultural history and drinking guide, Berkeley: Ten Speed Press, p. 264, ISBN 978-1-58008-745-2
- ^ The Dong Ding Mountain Tea Growing Region of Taiwan from TeaFromTaiwan.com, retrieved 4 April, 2009