Black and green teas come from the leaves of the camellia sinensis plant. To produce black tea, the leaves are plucked from the new growth of the plant, rolled, chopped and allowed to ferment before being roasted. Green tea leaves are left whole and allowed to air-dry before heating to end the oxidation process. Both types of tea contain a variety of polyphenols which act like antioxidants in the body. Black and green teas also contain varying levels of energy boosting caffeine, with black tea containing the most.
Tea leaves contain three main types of polyphenols, which are credited with helping prevent chronic diseases: catechins, theaflavins and thearubigins. The amount of each type of polyphenol present in 1 cup of tea depends on the type of tea. Green tea tends to be high in catechins and lower in the other two. Black tea offers more of the larger, more complex theaflavins and thearubigins, but fewer catechins.
The processing that tea leaves undergo most affects their polyphenol content, according to a study by the United States Department of Agriculture (USDA). Fermented black teas contain “99 times more theaflavins and 45 times more thearubigins” than green tea, for instance. If a black or green tea undergoes decaffeination, this decreases its level of catechins.
Tea leaves also contain flavonols. Flavonols are another class of polyphenols present in tea leaves. Both black and green teas contain them in comparable amounts. The three flavonols found in tea leaves are kaempferol, quercetin, and myricitin. Flavonols, like the other polyphenol constituents of tea, are linked to improved cardiovascualr health, decreased inflammation in the body and resistance to disease. The USDA study states that a tea’s flavonol content does not change with fermentation or decaffeination of the tea leaves
Tea leaves that undergo longer periods of fermentation, or oxidation, contain higher levels of caffeine. Since green tea leaves are processed before they begin to ferment, their caffeine content is much lower than that of fully fermented black tea leaves. Black tea leaves contain approximately two to three times the level of caffeine present in green tea leaves, according to the University of Maryland Medical Center. A cup of black tea contains an average of 42 to 72 milligrams of caffeine per 8-ounce cup. A cup of green tea contains an average of 9 to 50 milligrams of caffeine per 8-ounce cup.
The amount of time a cup of tea steeps also affects the amount of caffeine extracted into the final drink. Longer steeping time means higher levels of caffeine. On average 50 percent of the caffeine content in a cup of tea is extracted in the first 20 to 30 seconds of steeping. This stands true for the first minute. Five minutes of steeping results in an additional 1 to 2 milligrams of caffeine being extracted into the cup with diminishing returns with each minute of extraction time added. After six minutes or more of steeping time, a point of stasis occurs where the amount of caffeine in the tea leaves equals that of the water in which they are immersed.
A decaffeinated cup of tea is not a caffeine free cup of tea. Tea releases its caffeine content as it is steeped in cold, warm, hot or boiling water. The final amount of caffeine present in a cup of brewed tea varies depending on the initial caffeine content of the dry leaves, the temperature of the steeping water and the length of time the tea steeps. To decaffeinate a cup of tea, some people recommend completing a brief initial steeping of the tea for 20 to 30 seconds then making a second infusion using the same leaves. This may decrease the amount of caffeine in the final cup, but it is not very scientific. The actual amount of caffeine remaining is indeterminable without testing. Tea also comes in decaffeinated varieties. These teas typically undergo a commercial chemical decaffeination process that renders a cup of tea containing 1 to 12 grams of caffeine.
Boost the Healthful Benefits of Your Cuppa
Research published by the “European Heart Journal” in 2007 used black tea to show that adding milk to tea blocks its beneficial effects on heart health. One of polyphenol types found in tea, catechins, assist with vascular relaxation, keeping veins open and resulting in improved circulation. They also bind with the milk protein, casein, making the biochemical benefits of catechins unavailable to the body. If you are drinking tea for health reasons, it is best to drink it without milk.
Doctors have also learned that lemon tea, tea containing the citrus peel, seems to have a role in preventing skin cancer. A study conducted by the Dartmouth Medical School in 2007 discovered that black tea drinkers experienced a significantly lower incidence of certain types of skin cancer — up to 65 percent lower. Those who added lemon peel to their tea experienced an additional increase in protection up to 5 percent greater due to the active phytochemicals and nutrients present in lemon peel.