The risks associated with green tea are the same as those associated with any other kind of tea (common black tea, White Tea etc.) and are primarily due to the content of caffeine and tannin. The contraindications may vary with the percentage of caffeine and tannins in it. Most people might be familiar with these adversities, but it is still important to review and summarize the components responsible, as well as the associated risks.
Japanese green teas have a thin, needle-like shape and a rich, dark green color. Unlike Chinese teas, most Japanese teas are produced by steaming rather than pan firing. This produces their characteristic color, and creates a sweeter, more grassy flavor. A mechanical rolling/drying process then dries the tea leaves into their final shape. The liquor of steamed Japanese tea tends to be cloudy due to the higher quantity of dissolved solids.
^ Jump up to: a b c "Scientific Opinion on the substantiation of health claims related to Camellia sinensis (L.) Kuntze (tea), including catechins in green tea, and improvement of endothelium-dependent vasodilation (ID 1106, 1310), maintenance of normal blood pressure (ID 1310, 2657), maintenance of normal blood glucose concentrations (ID 1108), maintenance of normal blood LDL cholesterol concentrations (ID 2640), protection of the skin from UV-induced (including photo-oxidative) damage (ID 1110, 1119), protection of DNA from oxidative damage (ID 1120, 1121), protection of lipids from oxidative damage (ID 1275), contribution to normal cognitive function (ID 1117, 2812), "cardiovascular system" (ID 2814), "invigoration of the body" (ID 1274, 3280), decreasing potentially pathogenic gastro-intestinal microorganisms (ID 1118), "immune health" (ID 1273) and "mouth" (ID 2813) pursuant to Article 13(1) of Regulation (EC) No 1924/2006". European Food Safety Authority. 8 April 2011. Retrieved 9 November 2014.
contains antioxidants, including polyphenols such as epigallocatechin gallate (EGCG), which can powerfully quench damaging “free radicals,” metabolic byproducts that are chemically reactive and can damage cells. According to a study published in the European Journal of Clinical Nutrition, the polyphenols found in green tea provide six times the radical-quenching potential of those found in black tea.
University of Hong Kong researchers published a study in the August, 2009 Journal of Agricultural and Food Chemistry concerning green tea and bone health. When the bone cells of rats were exposed to green tea catechins, EGC in particular stimulated an enzyme that promotes bone growth by 79 percent. The catechins also increased bone mineralization and weakened the activity of cells that reabsorb bone rather than form it. (10)
Green tea is processed using either artisanal or modern methods. Sun-drying, basket or charcoal firing, or pan-firing are common artisanal methods. Oven-drying, tumbling, or steaming are common modern methods. Processed green teas, known as aracha, are stored under low humidity refrigeration in 30- or 60-kg paper bags at 0–5 °C (32–41 °F). This aracha has yet to be refined at this stage, with a final firing taking place before blending, selection and packaging take place. The leaves in this state will be re-fired throughout the year as they are needed, giving the green teas a longer shelf-life and better flavor. The first flush tea of May will readily store in this fashion until the next year's harvest. After this re-drying process, each crude tea will be sifted and graded according to size. Finally, each lot will be blended according to the blending order by the tasters and packed for sale.
A book written by Lu Yu in 600-900 AD (Tang Dynasty), "Tea Classic" (simplified Chinese: 茶经; traditional Chinese: 茶經; pinyin: chájīng), is considered important in green tea history. The Kissa Yojoki (喫茶養生記 Book of Tea), written by Zen priest Eisai in 1211, describes how drinking green tea may affect five vital organs, the shapes of tea plants, flowers and leaves, and how to grow and process tea leaves.
According to the National Cancer Institute, the polyphenols in tea have been shown to decrease tumor growth in both animal and laboratory studies. Researchers believe that it is the high level of polyphenols in tea that help kill cancerous cells and stop them from growing, although the exact mechanism by which tea inhibits and prevents cancerous cells is uncertain.
The polyphenols in green tea, which include multiple subcategories of polyphenols like flavonoids and catechins, can reduce the formation of free radicals in the body, protecting cells, molecules, and other structures from damage. One of the most active and powerful antioxidant polyphenols in green tea is epigallocatechin-3-gallate (EGCG). EGCG has been studied to treat a wide variety of diseases and may be one of the main reasons green tea has such powerful medicinal properties. Beyond EGCG, other polyphenol catechins in green tea include catechin, gallocatechin, epicatechin, epigallocatechin, and epicatechin gallate.
The most popular, widely consumed types of green teas hail from the places where green tea originated: China and Japan. Green teas from China and Japan have different flavor profiles based on where and how they are grown, but most distinctively how they are processed—pan fired in China and steamed in Japan. Other countries producing green tea typically take cues from China or Japan and adopt one of these country’s tea production styles.
Shade grown: All matcha is made from shade-grown tea leaves—a labor-intensive process where tea bushes are protected from the sun and light is filtered to the bushes in a very controlled manor. Shading boosts the chlorophyll production in the plant, giving the leaves a rich green color. The lack of sun reduces the plant’s photosynthesis of the leaves, which in turn alters the naturally occurring levels of caffeine, flavanols, sugars, antioxidants, and theanine. By controlling the sun exposure, tea producers can significantly alter the chemical make-up and flavor of the final tea leaves.