Chemically, caffeine is a member of the xanthine family. Caffeine is odorless, has a bitter taste and is highly soluble in hot water. Caffeine occurs naturally in coffee, tea, cocoa, kola nuts and a variety of other plants.
In moderation, caffeine has beneficial effects on the body: it increases alertness, stimulates metabolism and contributes to an increase in dopamine levels in the blood, which improves mood.
How much caffeine does a cup of tea contain?
The simple answer is: it depends. There are two main variables that influence the caffeine content of a cup of brewed tea: the type of leaf and the tea preparation method.
First, letís examine the type of leaf. On average, tea leaves contain 3% caffeine by weight, although this can range from 1.4% to 4.5%. Many factors determine the caffeine content in the dry leaf, such as soil chemistry, altitude, type of tea plant, position of the leaf on the tea bush and cultivation practices. For example, the young bud and first leaf generally have slightly more caffeine than leaves picked from the lower part of the tea bush. The leaves from the small leaf China tea plant (camellia sinensis) tend to have lower caffeine levels than the leaves from the large leaf Assam tea plant (camellia assamica). One factor that does not impact caffeine level is the level of oxidation. Green, oolong, black and white teas all contain caffeine. No one category of tea has more or less caffeine than another. Again, it all depends on the particular tea in question.
Next, letís take a look at the tea preparation method. There are many parameters that affect caffeine content such as the amount of leaf, the leaf particle size, water temperature and steeping time. For example, tea steeped in hot water for a longer time will release more of its caffeine than tea steeped with cooler water for a shorter period. A smaller leaf tea will release more of its caffeine than a larger leaf tea.
A Department of Nutritional Services report provides the following ranges of caffeine content for a cup of tea made with loose leaves:
Black Tea: 23 - 110 mg
Oolong Tea: 12 - 55 mg
Green Tea: 8 - 36 mg
White Tea: 6 Ė 25 mg
How can I lower the amount of caffeine in my cup?
For those who are sensitive to caffeine, we recommend using a little less leaf and brewing your teas with slightly cooler water for a shorter period of time. Green, white and lightly oxidized oolong teas are good choices, as they tend to benefit from lower water temperatures and shorter steeping times.
Since nearly 80% of the caffeine will be extracted within 30 seconds of steeping, you can easily remove most of the caffeine in any tea by following these guidelines:
Steep the tea in hot water for 45 seconds. Discard the liquid. Then, add water to the leaves and brew for the amount of time that is appropriate for that particular tea.