Tea and caffeine

The determinants of the caffeine level in a tea

Many tea drinkers are interested in the caffeine levels in various teas. The caffeine level of a tea is determined by the following factors:

• The tea plant species, various tea plants can have various levels of caffeine
• The tea leaves: young tea (green tea, white tea and some black tea) leaves tend to have higher level of caffeine than the mature leaves (Oolong teas and some black tea)
• Level of fermentation: the fermented teas (black tea and Oolong tea) tend to have higher level of caffeine than the unfermented teas (green tea and white tea)
• The tea baking time: the longer a tea is baked, the more the caffeine is evaporated (some Wuyi Oolong and some black tea)
• Matcha has the highest level of caffeine, as the entire leaves are consumed instead of the tea brew only
• The longer a tea is brewed, the more caffeine is resolved in the water

The caffeine levels of various teas:

Following are the average caffeine levels of various teas in comparison to equivalent amount (1 cup) of coffee:

• Coffee: 80mg(range from 40-170mg)
• Black tea: 40mg(range from 25-110mg)
• Oolong tea: 30mg(range from 12-55mg)
• White tea: 6-55mg
• Green tea: 20mg(range from 8-30mg)
• Pu-erh tea: 2mg (very low)

(https://goodluck2u.pixnet.net/blog/post/36239214)

Thumb of rule

It is generally believed a normal cup of tea contains about one quarter of the caffeine contained in the equivalent volume of drip coffee.  

It is also recommended to consume teas in such a sequence based on the caffeine level of feasible:

• Morning – black tea
• After lunch – green tea or white tea
• After dinner – Pu-erh tea

How to reduce caffeine level if needed

Since caffeine infuses early, there is a procedure available for those wishing to minimise their caffeine intake:

• Rinse the tea leaves with hot water
• Dispose this liquid which contains the most of the caffeine
• Brew the remaining tea leaves ( 0.5-1 minutes before drinking).

Some relevant articles:

Caffeine: http://www.abc.net.au/health/library/stories/2006/04/27/1829125.htm