Caffeine from natural sources has been consumed and enjoyed by humans throughout the world for centuries. The widespread natural occurrence of caffeine in a variety of plants undoubtedly played a major role in the long-standing popularity of caffeine incorporated products, especially the beverages.
The human body requires a certain amount of caffeine and research indicates that up to 10 – 12 cups of tea daily will not have any detrimental effect on the body. The species or the variety of the tea plant determines content of caffeine in tea, as it is a genetic feature. Camellia Sinensis, the variety that is grown in Sri Lanka has caffeine levels of approximately 2.5 – 4%. However the distribution of caffeine in the plant depends on the part of the plant it is derived from.
Bud 4.70 %
First leaf 4.20 %
Second Leaf 3.50 %
Third Leaf 2.90 %
Upper stem 2.50 %
Lower stem 1.40 %
Both tea and coffee contain the methylated xanthines, caffeine, theophylline and theobromine. Brewed coffee is said to have the highest caffeine content among those dietary items containing caffeine- approx. 100 mg per cup. A 300-ml bottle of cola has 30- 60-mg caffeine and approx. 37-mg caffeine is there in 56g dark chocolate bar. There are a wide variety of drug products that contain caffeine- typically 200 mg per tablet or capsule (pharmacologically active dose of caffeine). A cup of tea has approx. 28 –44 mg caffeine- (FDA 1980).
The quantity of caffeine in tea, on dry solids basis, is more than the quantity of caffeine in an equal weight of dried coffee beans. However, as a result of getting more cups of tea from a unit quantity of black tea than from an equal quantity of ground coffee beans, the quantity of caffeine per cup of tea is less than the caffeine in an equal cup of coffee.
Excessive caffeine is said to have adverse effects on the human system and brewed tea has only half the caffeine levels in brewed coffee. However, it is important to note that research proves that the presence of caffeine in tea does not produce unhealthy results due to its combination with tea polyphenols.
The Food Guide to healthy eating recommends caffeine consumption in moderation. According to the current findings for most people an intake of caffeine up to 400-450 mg per day does not increase the risk of heart disease, hypertension or have an adverse effect on pregnancy or the foetus. This level of caffeine is equivalent to approximately 10 to 12 cups (170 ml) of tea per day.
As explained by Prof. T. W. Wickremanayake (Ph D Glasgow, Visiting Research Fellow Glasgow, Wisconsin and California) the pharmacologically active dose of caffeine is 200 mg and the acute fatal dose is about 10,000 mg. Those who drink more than 5 cups of coffee or 9 cups of tea are regularly consuming 5% of the fatal dose. The T 1/2 of caffeine is about 3 hr. It is excreted quickly in urine as 1-methyl uric acid.
Prof. Wickramanayake also states the following. "There is a positive association between Myocardial infarction and heavy coffee consumption, whereas the correlation between infarction and heavy tea drinking is negative. In rats and rabbits maintained on atherogenic diets, caffeine increases serum lipid concentrations and therefore the incidence of atherosclerosis. Coffee has the same action but not decaffeinated coffee. Tea has the opposite effect to caffeine alone or caffeine in coffee. Similar results have been reported in a study of human subjects with and without heart ailments. Russian scientists have demonstrated that a course of tea consumption improved the condition of atherosclerotic patients. The alleged adverse effects of caffeine are apparently eliminated in tea either by a modification of its activity by other constituents, or by the opposing action of some anti-atherosclerotic constituent."
Taste, colour and mouth feel depend on the interaction between the two main components of tea, polyphenols and caffeine. Each component is astringent on its own, but as a complex the astringent character is reduced.
Water is known to contain dissolved gases absorbed from the air. Carbon dioxide (CO2) gas that is present in water affects the acidity. Acidity of water plays a critical role in the ionization of tea polyphenols and it contributes to the stability of the above complex.
CO2 in water is gradually released during the boiling process. Re-boiling will in fact further reduce CO2 levels, resulting in a decrease in the acidity. As mentioned above this will affect the caffeine and polyphenol complexion, and bring about changes in the colour as well as the character of the brew.
Twice boiled water will therefore affect the taste of a good tea and hence our request that only freshly boiled water is used for brewing Dilmah tea.
For teas to be labelled decaffeinated, the caffeine content should not exceed 0.4% by dry weight, which is equivalent to approximately 4 mg of caffeine per 170 ml serving.
The process of decaffeination extracts the caffeine in tea. The current commercially available methods for decaffeinating black tea are solvent based extraction using ethyl acetate or methylene chloride, and extraction using supercritical (solid) carbon dioxide. All three methods extract caffeine with minimum effect to the quality of tea.
Tea composition varies with climate, season, horticultural practices and variety. Polyphenols are the most important component in tea, as they constitute approximately 36 percent of the dry weight of tea. Other components of fresh green leaf include caffeine, protein and amino acids, carbohydrates, lipids, vitamins and minerals.
Green and black tea have similar chemical make-up. The primary difference between the two types lies in the chemical changes that take place during their production. In black tea the plant Polyphenols are oxidized and this is prevented in the manufacture of green tea.
One of the most important groups of Polyphenols in tea is the catechins in green tea, theaflavins and thearubigens in black tea. A variety of physiological effects have been attributed to tea catechins which are currently best known for their antioxidant activities.
Black tea is all-natural (non flavoured) and contains no additives. It is virtually calorie-free (1 calorie per 100 ml) and sodium free and is therefore a suitable beverage for individuals on calorie-reduced or low sodium diet. Tea includes fluoride, traces of vitamins A, K, C, B carotene and B vitamins.
Average daily consumption of tea in the United Kingdom, 3.43 cups (650 ml), provides very few calories and only a small amount of fat, whilst contributing valuable minerals and vitamins to the diet. It provides:
- Over half of the total intake of dietary flavonoids.
- Nearly 16% of the daily requirement of calcium
- Almost 10% of the daily requirement of zinc
- Over 10% of the folic acid need
- Around 9%, 25% and 6% of vitamins B1, B2 and B6 respectively.
The water used to brew the tea significantly affects the colour and the taste of a cup of tea. Tea brewed in soft water or permanently hard water (which contains CaSO4) appears brighter than if it is brewed in temporary hard water (that contains Calcium bicarbonate CaCO3). High pH water that contains bicarbonate makes the infusion look darker brown due to the greater ionisation of the tea polyphenols. While lower pH as in lemon tea the infusion turns yellow. As for taste some teas are more suited to softer water such as the orthodox manufactured Assam leaf, while high grown Ceylon and CTC manufactured teas are better with temporary hard water.
Boiling water for too long does dramatically affect the quality of tea. The desirable brisk taste of tea is created by the interaction of two of its main components, caffeine and polyphenols. Each component is harsh on its own but as a complex the compounds moderate each other. Acid levels of water affect the behaviour of these components.
Water contains minerals and gases absorbed from the earth bed and air. Carbon dioxide absorbed by air makes the water slightly acidic that influence the colour and taste. High temperature changes the acidity of water and the acidity is reduced by gradually driving out carbon-dioxide. Therefore re-boiled water might well brew tea of a different colour and strength and is unsuitable to brew a good cup of tea
Herbal Infusions, fruit based tisanes and floral infusions are not tea. There are only three types of tea, black tea, green tea and Oolong tea. In many countries, notably the USA, these infusions are usurping the health and other benefits of tea falsely. We give below a brief introduction to the most popular herbal infusions. Dilmah offers a selection of three herbal infusions, clearly differentiated from Dilmah black and green teas.