Wu long tea, sometimes called oolong tea, is a semi-fermented tea produced largely in China and Taiwan. The leaves of the camellia sinensis plant, or tea tree, are plucked and immediately processed. The processing includes a controlled oxidation, or fermentation, period during which oxygen interacts with the cells of the leaf and change the chemical composition. The amount of oxidation varies from region to region and can range from as little as 12 percent to as much as 70 percent. The amount of fermentation that the leaf undergoes does effect the caffeine content of the tea but there are many differing views as to the amount of caffeine in wu long tea. Estimations range from 12 to 55 mg of caffeine in 8 oz. of wu long tea.
Misconceptions
A common misconception is that the more fermentation that a tea undergoes the more caffeine it will contain. Generally, the fully fermented black tea is considered to have the most caffeine, followed by wu long, green tea, and white tea. Even in among researchers, studies have shown varying concentrations of caffeine in each of the families of tea. Contradicting anecdotal accounts have also linked different energizing effects with each tea; some find wu long to be relaxing, while others report it to be stimulating.
Affected by Preparation Method
A study published in "Food Research International" tested the caffeine content of black, green, wu long, and herbal teas. The researchers found that the concentration varied based on the size of the leaves, with the broken leaves of tea bags containing less caffeine than the whole loose tea leaves. It was also revealed that the length of steeping time affects the amount of caffeine released from the leaves. A brief, 30-second steep extracted only 9 percent of caffeine while 15 minutes removed all of the caffeine from the leaf. The water temperature may also contribute to caffeine content. Caffeine is water soluble at higher temperatures. Water and green tea are traditionally steeped for a shorter period in cooler water than black and wu long teas.
Types of Tea
The type of tea tree, age of leaf, time of harvest and method of storage can all have a bearing on caffeine content. The first leaves to be picked, such as those used for green tea, contain more caffeine then those allowed to age on the plant, which are typically used for wu long tea. Tea trees grown from seed tend to have more caffeine than those propagated through cloning.
Affected By Other Compounds
In addition to caffeine wu long also contains an amino acid called L-theanine which has a calming effect, counteracting the stimulation of the caffeine. Japanese researchers found that L-theanine stimulates the release of alpha brainwaves, associated stress reduction and relaxation.
Expert Insight
According to a study published in "The Journal of Medical Investigation" wu long tea had a greater effect on energy expenditure than green tea despite having less caffeine. These results suggest that caffeine is not the only component responsible for the stimulating effects of tea.
References
- "Food Research Internation": Tea Preparation and its Influence on Methylxanthine Concentration; August 2002
- The Tea Companion; Jane Pettigrew; 2004
- Noble Harbor: Caffeine in Tea vs. Steeping Time
- "Nippon Nogei Kagakukaishi ": Effects of L-theanine on the Release of α-brain Waves in Human Volunteers; 1998
- "The Journal of Medical Investigation": Oolong Tea Increases Energy Metabolism in Japanese Females;
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