The Commonly Asked Questions About Tea

All tea, whether black, green or oolong, comes from the leaves of the Camellia sinensis plant. Camellia sinensis is evergreen in most countries and thrives in semi-tropical climates. There are reported to be over 2,000 types of tea. The differences result from the climate, the growing region, the soil conditions, where the tea is grown and the processing which the tea undergoes.

Next to water, tea is the world’s most popular beverage. For thousands of years, billions of people have enjoyed tea experiencing not only the pleasure but also potential health benefits.

What's the difference between green, black and oolong teas?

The difference between green, black and oolong teas results from the method of processing the leaves of Camellia sinensis undergo. Black tea is produced when newly harvested leaves are crushed or torn and exposed to the air. The leaves undergo a natural enzymatic process—the enzyme polyphenoloxidase contained within the leaf is exposed to oxygen when the leaves are crushed/torn. This then changes the colour of the leaves from green to a coppery brown and after drying or "firing" to black.

Green leaves are typically heated with steam or parched which stops any enzymic activity. The leaves are then dried. The resulting dry (green) leaf produces a tea liquor which is pale green. Oolong tea is produced using the same process as black tea, however the time for enzymatic development is shorter than for black tea. Oolong tea produces a liquor that is midway in flavour and colour between green and black tea.

What's the difference between herbal teas and black, green and oolong teas?

Herbal teas do not in general contain leaves from Camellia sinensis and therefore are not regarded as true teas. Herbal teas are either pure or mixtures of plant leaves, flowers or roots, spices and herbs, fruit flavours and/or fruit components. A more accurate name for herbal tea is herbal infusion. Herbal infusions do not contain the same antioxidants found in tea produced from Camellia sinensis. Since herbal infusions come from a mixture of ingredients such as spice, fruits and berries from various plants, it is likely that some contain antioxidant components.

What is the link between tea and health?

Tea contains antioxidants called flavonoids which may protect against free radicals. Free radicals damage healthy cells and tissues and are generated by normal body functioning and from external stimuli such as UV light, smoking and chemicals. Research suggests damage from free radicals may contribute to the development of chronic diseases and strokes. Antioxidants inhibit the activity of free radicals. Emerging scientific evidence associates tea drinking with health benefits, however research is continuing to look for a link between drinking tea and optimising health. Evidence to date indicates that drinking tea in particular may help maintain good cardiovascular function contributing to a reduced risk of cancer and heart disease.

What are the antioxidants in tea?

Flavonoids are the main type of antioxidants found in tea. The amount and type of flavonoids in tea depend on the variety, manufacturing processes and brewing habit. Catechins, a group of flavonoids, are found in all teas but are particularly high in green tea. During fermentation (the enzymatic process) of green leaf to black tea, the catechins are converted to more complex flavonoids—theaflavins and thearubigens. Oolong tea contains antioxidants that are found in both green and black tea. Scientific research suggests that the flavonoids in green, black and oolong tea have similar antioxidant activity. Most scientific research has been based on the study of catechins because they can be easily isolated and can be detected within a living organism.

What are tannins?

Tannin is a general term for flavonoids found in tea. Polyphenols is also a term that refers to a specific chemical structure of the antioxidant compounds in other foods. However, tea flavonols show specific antioxidant properties not found in other foods.

Is the antioxidant level in all tea the same?

All teas are a good source of antioxidants. Research suggests that tea grown in different regions contain varying levels of flavonoid antioxidants. The length of brewing time will affect the release of flavonoid antioxidants. The majority of flavonoids are released within two minutes of brewing. The method of brewing also affects the amount of antioxidant in each cup of tea. Swirling tea bags within the cup tends to release the flavonoids faster than stationary tea leaves brewed in a teapot. This is why it is advised to stir the brewing tea leaves inside the pot a few times before pouring out the tea.

Does the addition of milk affect the antioxidant level?

Emerging evidence suggests that there is no effect on the absorption of tea flavonoids, or catechins. Research conducted by Commonwealth Scientific Industrial Research Organisation (CSIRO) in 1997 also showed that the addition of milk to black tea did not affect the antioxidant activity.

Which foods have a high antioxidant potential?

Overall, fruits, fruit juices, vegetables, tea and red wine have a high antioxidant potential. Research completed by CSIRO showed that in the Australian diet, brussel sprouts, plums, prune and grape juice, tea, coffee and red wine are the main sources of antioxidants.

Another study conducted at the US Department of Agriculture Human Nutrition Research Center on Aging found that tea and many vegetables have a high antioxidant capacity. In fact, black and green teas had much higher antioxidant activities against peroxyl radicals than any vegetables tested.

Does tea consumption impact iron absorption?

The flavonoids in tea like other compounds in food such as phytates in cereal partially inhibit iron absorption when consumed with food. Only non haem iron, that is iron from plant sources not animal sources is affected. This effect can be reduced significantly by the inclusion of a Vitamin C rich food and drinking orange juice. In Western countries there is no indication that tea consumption causes iron deficiency. Risk groups for iron deficiency anaemia (young children and pregnant women) are encouraged to eat diets rich in iron and Vitamin C.

Does tea affect cholesterol levels?

Most animal and human trials have not shown a positive effect on blood cholesterol levels. Test tube (in vitro) tests have shown that the antioxidant flavonoids in tea protect cholesterol from oxidation. It is the oxidation of cholesterol that is thought to contribute to the formation of arteriosclerosis—an arterial disease particularly in the elderly characterised by inelasticity and thickening of the blood vessel walls with lessened blood flow.

What about caffeine in tea?

The caffeine level in tea depends on preparation method, brewing time and to some extent the variation in the tea plant itself. Caffeine content of tea brewed to Australian conditions is less than that of brewed coffee. Green tea has about the same amount of caffeine as brewed black tea. However like all tea, the amount of caffeine is influenced by brewing, preparation and amount of leaves used. Extensive research has found no association between moderate caffeine consumption and the risk of chronic disease.

Does drinking tea increase the risk of kidney stones?

It is often incorrectly assumed that tea contains large amounts of oxalate, which contributes to kidney stone formation. On the contrary, according to a major study at Harvard, the risk of kidney stone formation actually decreases as tea consumption increases.

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