Tea and caffeine
What is caffeine and how does it effect the body?

Chemically, caffeine (1,3,7 – trimethyl xanthine) is an alkaloid and a member of the xanthine family. It is odourless, non-toxic, has a bitter taste and is highly soluble in hot water.

Caffeine occurs naturally in coffee, tea, cocoa, mate (Ilex paraguarensis), kola nuts and a variety of other plants.

Some plant species that contain caffeine such as tea and coffee may also contain trace amounts of another alkaloid called theophylline that is a relative (analog) of caffeine.  Unlike caffeine, theophylline has only two methyl groups.  Theophylline has a stronger effect than caffeine on the heart and breathing.  Some species related to tea, also contain another alkaloid called theobromine.  This alkaloid is largely found in Cocoa where its concentration is about 7 times that of caffeine.  Theobromine has weaker stimulating effect than caffeine.

 

 
Caffeine is bioactive and in moderation, it has beneficial effects on the body; it increases alertness, serves as a bronchial dilator, stimulates metabolism and contributes to an increase in dopamine levels in the blood, which improves mood.    However, at high levels it can cause restlessness, insomnia and anxiety.  It can also exert some mild withdrawal effects such a transient but persistent headache and inability to concentrate and can be addictive. Caffeine is the most widely consumed stimulant drug in the world.

Research has shown that caffeine is rapidly absorbed following oral consumption.  Peak blood (plasma) levels are achieved usually within 30 minutes.  It is metabolized in the liver.  It has a very short half life of only about 3 – 5 hours in adults and is easily excreted in the urine.  Because of its short half life in the body one needs to keep coming back for more.  It causes stimulation by antagonizing the effect of adenosine (which causes a calming effect).  Because of its pharmacological properties, caffeine is used in the pharmaceutical industry and is often a component of several over the counter analgesics. Caffeine is added to several types of commercial drinks including Cola and pepper soft drinks, energy drinks, frozen desserts, chocolates and candies.

 


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.


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, the altitude in which the tea is planted, type of tea plant (clone), position of the leaf on the tea bush and cultivation practices (i.e. agronomic practices in a tea field). 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 leafed Chinary clones (Camellia sinensis var. sinensis) also tend to have lower caffeine levels than the leaves from the large leafed Assam tea plant (Camellia sinensis var. assamica). Apparently, caffeine level is not affected in any way by the level of oxidation during tea manufacture. 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 clone or variety in question.  A standard cup of tea will contain an average of about 50mg of caffeine with a cup of coffee having 65-175mg and a bar of chocolate about 1-35mg.


There are many parameters that affect caffeine content such as the amount inherent in the leaf (genotype), 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.


For consumers who are sensitive to caffeine, it is recommended that they use a little less leaf and also brew their 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 most of the caffeine (nearly 80%), is extracted within the first 30 seconds of steeping, one 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.

Studies done at the Tea Research Foundation of Kenya (TRFK) have shown that the contents of caffeine in commercialised tea clones in Kenya range from 1.6% to 4.9%. The most popular clone in the smallholder sector, clone TRFK 6/8, has caffeine content of 1.65%. This clone owes its popularity to production of high quality black tea, which research has shown, is associated with high levels of total polyphenols. Overall, most tea clones cultivated in Kenya and their resultant tea products can be considered medium to low in caffeine content (≤ 3.0%). Efforts to develop naturally caffeine-free tea or teas with trace amounts of caffeine are ongoing. The TRFK has been using conventional breeding approaches to develop low to caffeine free tea clones, though there are other biotechnological techniques which can also be used to shut down or down regulate the major gene that catalysis the biosynthesis of caffeine in tea.  Such tools have as yet not been used at the TRFK.  In the TRFK plant improvement programme, there currently exists some inter-specific hybrid clones that are at various stages of development. The generated wide crosses are expected to segregate for leaf caffeine content.  A parent used in these wide crosses has a caffeine content of 0.3%. Clones from these hybrids will soon be subjected to caffeine characterization and their suitability for black and green tea processing determined collaboratively between professional tea tasters and TRFK. Through these efforts, it is envisaged that a caffeine-free tea clone will be selected and made available to the market in about five years.  Hybrids potentially with theobromine have also been developed at TRFK.