It is the caffeine that gives tea its ability to refresh us, increase our ability to concentrate and keep us going through the day. Caffeine is a stimulant that helps increase the speed of our reactions, makes us more alert, stimulates the digestive system and the activity of the kidneys and so helps to clean the body of unwanted toxins. There is an important difference in the way in which we absorb the caffeine in coffee and the caffeine in tea. When we drink coffee, the caffeine content goes instantly into our circulatory system, jolting us into wakefulness, causing the pulse to beat faster and the blood to pump more vigorously around our bodies. When we drink tea, the caffeine is released much more slowly (because of the controlling effects of the other ingredients in the tea) and takes 15 to 20 minutes to be absorbed. So, instead of being released into the bloodstream, the caffeine goes more gently into our central nervous system and helps to heighten our senses and increase our wakefulness. The effects of the caffeine in tea are therefore felt more slowly, stay with us for longer and tail off more gradually than with coffee. Tea really is a much more efficient 'pick-me-up'.
Caffeine is a mild cardiac stimulant and a mild diuretic and can cause problems for people with heart or kidney conditions. For those who cannot or do not wish to take caffeine into their bodies, decaffeinated tea is readily available, although the quality and flavour vary considerably, depending on the decaffeination process. Three different methods are used to remove the caffeine - carbon dioxide, methylene chloride and ethyl acetate.
Carbon dioxide is an organic solvent that is cheap to use, easy to remove from the tea after decaffeination, and harmless in small quantities. C02 is pumped into a chamber containing tea and it bubbles through the tea solution to remove the caffeine. The C02 is then removed from the chamber, separated from the caffeine and reintroduced into the chamber to absorb more caffeine. This process is repeated several times. The benefits of this method are that no chemical residue is left in the tea and the flavour and tea compounds are relatively unharmed.
Methylene chloride is the most popular and most widely used agent to extract caffeine from tea and is easily removed from the tea after decaffeination. It is approved by the American food standards body, the FDA (the Food and Drug Administration section of the US Department of Health and Human Services). To decaffeinate tea, the methylene chloride is applied either directly or indirectly to the tea. During the 'direct' method, the methylene chloride is applied to wet tea leaves and then removed with the caffeine. The decaffeinated leaves are then washed and dried. During the 'indirect' method (whereby the methylene chloride never comes into contact with the tea itself), the tea is first soaked in water to extract the caffeine (and other tea ingredients such as polyphenols and oils that give the tea its flavour and health benefits). The caffeine and water are then mixed with methylene chloride and heated to evaporate the caffeine and methylene chloride, leaving water and tea extracts which are then reintroduced to the tea.
Ethyl acetate is classed as a natural element that is found in tea, coffee, wine and bananas and is used in flavour enhancers for ice-creams, confectionery, cakes and perfumes. Because it occurs naturally, some people consider it to be the best agent for decaffeination and the FDA considers it to be GRAS (Generally Regarded as Safe). However, during the decaffeination process, it extracts other components as well as the caffeine and is difficult to remove from the decaffeinated tea.