Caffeine in Oolong Tea (2020 Guide)

November 01, 2020 0 Comments

Does Oolong Tea have caffeine? Yes, but...

How much caffeine is in Oolong Tea isn't as cut and dry as you might think. It's not just simply a listing of the the milligrams of caffeine in a cup of tea. How much caffeine is in Oolong Tea is affected by brewing temperature, ratio of water to leaves, brewing method, and the specific type of tea. All of these factors, and more affect caffeine content.

Here we've put together a comprehensive guide to how much caffeine is in your cup of Oolong Tea.

Oolong Tea Caffeine

Pure caffeine

Does Oolong Tea have caffeine? Yes it does, but the amount that gets into a cup of tea depends on a lot of factors. Pictured above is pure caffeine. 

Taiwan’s Tea Research and Extension Station (TRES) measured the caffeine content of a number of Taiwan teas after brewing at different temperatures. The following table summarizes the results for tea prepared with boiling water. 

Caffeine in an 8oz. (237ml) Cup of Tea (Boiling Water)

 Tea Type Caffeine (mg)
High Mountain Oolong 63
Wenshan Baozhong 68
Dong Ding Oolong 69
Green Tea 94
Black Tea 99
Oriental Beauty 102

There are are many factors that affect the final caffeine content in a cup of Oolong Tea, so let's delve into the details below.

Brewing Temperature

Pouring tea from a teapot into a tea cup

The temperature of the brewing water is one of the biggest factors in determining the caffeine content of a cup of tea. Taiwan’s Tea Research and Extension Station (TRES) measured the caffeine content of a number of Taiwan teas after brewing at different temperatures. The teas were brewed using 3g of tea in 150ml water, using temperatures of 80°C, 90°C, and 100°C (boiling) water for 5-6 minutes. Only the first steeping of each was used to measure caffeine. The teas examined were as follows and the results plotted in Graph 1.

  1. Bilochun Green Tea, spring harvest, Qing Xin Gan Zai strain.
  2. Wenshan Baozhong Tea, fall harvest, Qing Xin Oolong strain.
  3. High Mountain Tea, fall harvest, Qing Xin Oolong strain.
  4. Dong Ding Oolong Tea, fall harvest, Qing Xin Oolong strain.
  5. Oriental Beauty Tea, summer harvest, Qing Xin Da Mao strain.
  6. Black Tea, fall harvest, Tai Cha #8 strain. 

Caffeine Content vs. Steeping Temperature for Various Teas

Graph 1. Caffeine Content vs. Steeping Temperature for Various Teas
Source: Taiwan Tea Research and Extension Station

As Graph 1 clearly shows, boiling water brew drew out the most caffeine for all types of teas. Incredibly, the caffeine released with boiling water was about double that of 80°C water for all tea types. Based on this information, an 8oz (237ml) cup of tea prepared with boiling water gives us the figures in first table above.

Number of Steeps

TRES also examined the effect the number of steepings had on caffeine content. Graph 2 shows the caffeine content of different steepings of Green Tea (three grams of Green Tea brewed in 150ml of water) under different temperatures and times. The third steeping of the hot brew had only 30% of the caffeine content of the first brew, and the 4th brew (not shown) only had 9%.

Caffeine Content of Green Tea vs. Number of Steepings

Graph 2. Green Tee Caffeine Content vs. Brewing Method
Source: Taiwan Tea Research and Extension Station

Cold Brew for the Least Caffeine

Furthermore, Graph 2 shows that Green Tea brewed at 4°C for intervals of two and four hours, undergoing repeated brews for a second and third interval, showed a much lower caffeine content that the hot water brewings. This goes to show just how much caffeine is easily dissolved in hot water. So people who are sensitive to caffeine, but still enjoy drinking tea, may want to use the cold brew method, or opt to drink only the second or third steeping of tea in hot water.

Cultivar and Growing Conditions

The caffeine content in tea leaves is also influenced by the cultivar, the position of the leaf on the tree, the growing season, climate, and overall growing conditions of the tea trees. Different cultivars of tea leaves can vary significantly in their caffeine content, and young leaves have higher concentrations than mature ones.

Harvesting tea leaves

The cultivar of the tea and the growing conditions affect caffeine content

Summer and fall growing seasons produce higher levels of caffeine content in the new leaves than spring and winter due to the more extensive growth during these seasons. More shaded leaves have relatively higher caffeine levels.

Roasting

Caffeine crystals on a tea roasting oven

Caffeine crystals on a tea roasting oven. Some caffeine comes off directly from the leaves when roasting and crystalize on the surroundings.

The heat of roasting tea leaves sublimates the caffeine, meaning it turns it directly into a gaseous form, releasing it into the air. This is evidenced by the crystallized caffeine that forms on the surfaces of the ovens and walls and ceilings of tea roasting rooms. Because of this, roasted teas, in general, will have less caffeine that unroasted teas. So if you’re looking for a robust flavor profile with less caffeine, explore the vast array of roasted Oolong Teas.

Aging

Tea aging in urns

Tea aging in urns

Aging tea leaves results in mellowing their flavor profile, and brings forth a deep, rich, sweet character that is reminiscent of both preserved fruit and smoked food products. And while the science behind this effect is yet to be full researched, it stands to reason that the bitter flavor of tea that is mostly due to caffeine content is slowly being transformed into different chemical compounds that offer a milder, sweeter flavor profile. So again, if you are looking for full bodied, rich, complex flavors in tea, but don’t want the caffeine boost, Aged Tea is a good choice. And in this respect, the more mellow and smooth the flavor profile is, the more likely there is less caffeine content in the brewed tea!

Conclusion

So, as you can see, there are many factors that go into determining how much caffeine is in a particular cup of tea. Here’s a summary:

  • Brewing tea at lower water temperatures releases less caffeine than boiling water.
  • Repeated steepings having increasingly less caffeine content.
  • Different cultivars and growing conditions have various influences on the caffeine content in tea.
  • Summer and fall harvests have higher caffeine content than spring and winter harvests.
  • Unroasted teas generally have higher caffeine content than roasted teas.
  • Aging tea presumably reduces the caffeine content in tea by slowly breaking down the caffeine.

If you enjoyed reading this post, check out our piece on how Taiwanese Oolong Tea is made in which we delve into the details of what makes Oolong Tea special.

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