What Is in Tea, Part One

The base of the flavour, the element that gives tea its savour, is the mineral content of the leaf.

Tea leaves contain a good balance of the macrominerals — potassium, calcium, magnesium, phosphorus — along with trace minerals such as zinc, manganese and selenium. In practice the composition and quantity vary a great deal with the type of tea, where it was grown and how it was cultivated.

Magnesium does dissolve into the liquor to some extent, but it is taken up far more efficiently from teas where the leaf itself is consumed — matcha, or leaves used in cooking.

The green of the leaf is the colour of chlorophyll, the pigment present in every plant that photosynthesises. In plant physiology it plays the central role of absorbing and converting light energy.

In human studies, chlorophyll and its derivatives have been associated with deodorising effects, and some research suggests anti-inflammatory and anti-carcinogenic action. Further study is needed on efficacy and mechanism in humans.

Magnesium sits at the centre of the chlorophyll molecule. So when the leaf itself, or its powder, is consumed — as with deep-steamed sencha or matcha — magnesium is taken in along with the chlorophyll.

One reason tea gives a sense of freshness may be ascorbic acid, that is, vitamin C. Vitamin C has strong antioxidant action and works to remove reactive oxygen species in the body.

Vitamin C is vulnerable to heat, light and oxidation. It breaks down and diminishes with heating above 60°C, with enzymatic oxidation during processing, and with exposure to light.

For this reason vitamin C tends to survive in green tea, which is unfermented and heat-treated at relatively low temperature by steaming or pan-firing. In black tea, where enzymatic fermentation (oxidation) is carried through completely, and in oolong, where it is halted partway, vitamin C is greatly reduced during processing.

Japanese sencha leaf contains roughly 60 mg of vitamin C per 100 g, though this varies with the product and the region. Black tea leaf, having lost most of it during manufacture, contains only a trace — a few milligrams.

Vitamin E (tocopherol) is the representative fat-soluble antioxidant vitamin. It prevents the oxidation of lipids and protects cell membranes and the vascular endothelium.

In tea it is present mainly in the waxy layer and the oils on the leaf surface, functioning as a natural defence against oxidation by light and oxygen. Very little vitamin E dissolves into an ordinary green tea liquor, but intake rises when the whole leaf is consumed, as with matcha. It has also been reported that it may work together with polyphenols such as catechins to ease oxidative stress throughout the body.

Beta-carotene is one of the carotenoid pigments in the leaf, converted in the body to vitamin A (retinol) as required. It coexists with chlorophyll as part of the photosynthetic pigment system, functioning as a photoprotective pigment that shields the chloroplasts from strong light.

Nutritionally, beta-carotene has antioxidant action and is involved in maintaining the health of skin and mucous membranes and in supporting vision. Being poorly soluble in water it hardly passes into an ordinary liquor at all, but it can be taken up where the leaf is consumed as powder or used in cooking.

High-grade sencha and matcha made from buds and young leaves are particularly rich in beta-carotene — something like receiving the light energy of the plant directly.

Next we turn to catechins, which likewise have antioxidant action.