Is Green Tea Caffeine-Free

Tea is becoming more and more popular around the world. Teahouses seem to open everywhere and ice tea consumption is also on the rise. Green tea, originally only known in Asia, arrived to Europe some decades ago. It is supposed to have a long list of favorable effects, which often include the lack of caffeine. Other sources 

Before going into more detail, some conceptual clarification about the liquids served in teacups may not be out of place. Tea is the drink made of the leaves of tea plant Camellia sinensis), but the word is often (mis)used to mean other drinks made by extracting various plant parts in hot water. Technically, this other drink should be called herbal tea or tisane (- 3.8). Tea itself is diverse enough, and this can only be appreciated in a specialized tea shop. Capsules and tablets containing tea extracts are also marketed today, and there are many misconceptions around these issues. 

The tea plant is an evergreen shmb native to Asia. A legend says that Buddha was the first to try it when a tea leaf fell into his cup. Another, better documented and earlier story credits Chinese emperor Shennong with the discovery, who again got a tea leaf in his cup of hot water accidentally in 2737 B. C. No matter what the origins, tea consumption has been a part of Asian culture for millennia, and it has probably contributed to preserving the health of those who consumed it. 

In Oriental medicine, tea was used against various illnesses. To begin with, drinking hot tea was a means of disinfecting water. But this is not the whole story. The main ingredients of tea are caffeine, theophylhne and theobromine ( 2.22). There is about 1-5 % of caffeine in dry tea leaves and this is mainly responsible for the stimulating effect. The other two notable alkaloids are present at much lower levels. The diuretic effect of tea also comes from caffeine and the essential oils in leaves give the pleasant flavor and aroma. 

The amount of caffeine in the drink is influenced by both the preparation method and the caffeine levels in the fresh tea leaves. Different hybrids of the tea plant and tea types may vary greatly in this respect (Table 3.5). 

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Green tea quality is dependent to a large extent on amino acid levels, especially that of theanine.97 Ascorbic acid content, although very low, also correlates positively with quality. Free reducing sugars and catechin gallates show a negative correlation.98 Caffeine levels do not have much effect on quality. 

In contrast to the decaffeination of coffee, which is primarily executed with green coffee, black tea has to be extracted from the fermented aromatic material. Vitzthum and Hubert have described a procedure for the production of caffeine-free tea in the German patent application, 2127642 [11]. The decaffeination runs in multi-stages. First, the tea will be clarified of aroma by dried supercritical carbon dioxide at 250 bar and 50°C. After decaffeination with wet CO2 the moist leaf-material will be dried in vacuum at 50°C and finally re-aromatized with the aroma extract, removed in the first step. Therefore, the aroma-loaded supercritical CO2 of 300 bar and 40°C will be expanded into the extractor filled with decaffeinated tea. The procedure also suits the production of caffeine-free instant tea, in which the freeze-dried watery extract of decaffeinated tea will be impregnated with the aromas extracted before. 

Although green tea usually contains less caffeine than black tea, it is by no means caffeine-free. A cup of black tea may contain as much as an espresso (about 100 mg). A cup of green tea typically contains about one third of this amount. High tatmin content in green tea slows down the take-up of caffeine and moderates the stimulating effect. Recent research shows that the presence of an amino acid named L-theanine is also significant (Fig. 3.25). 

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