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Why does my green tea become brown after being in my thermos for an hour or two?

My thermos is not rusting or rusted. It only happens when i put green tea in it.

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Answer #1

This, of course is based on my own knowledge..or possibly not!

The problem is the constant high temperature at which the tea is kept in a thermos. For instance, a cup of brewed tea left standing won’t lose too much “greenness,” even overnight. A teapot full of tea, however, will take on a slightly brownish hue. That’s because the pot holds the heat in longer than a cup. A thermos, obviously, retains heat much, much better.

Tea that turns too brown has lost much of its antioxidant content. That’s why green tea is healthier than oolong or black (English) teas, which are brown because the leaves were dried in the sun after harvesting and then allowed to ferment. Sun-drying allows an enzyme in green tea (called polyphenol oxidase) to oxidize (i.e., combine with oxygen in the air). The oxidized enzyme alters the disease-fighting catechins, which give the tea its green color. Fermentation also causes the catechins to be oxidized. Oxidized catechins give black tea its distinctive aroma and flavor but don’t have the health benefits of catechins in their natural state.

Consequently, when green tea is harvested, the grower’s first concern is to get the leaves to the steaming or frying vat as quickly as possible. This stops oxidation and fermentation, locking in green tea’s distinctive earthy flavor and aroma – and preserving the catechins.

But green tea’s catechins also begin to break down after brewing. (And sustained high temperatures, as in a thermos, only accelerate this process.) This is why I always recommend that people drink their green tea within an hour of brewing.

(And think of how long bottled, ready-to-drink green tea has been sitting around! Without artificial green coloring, it wouldn’t be green at all.)

Answer #2

._. well.

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