[Functional Food] Tea (Part 2)

February 24, 2022

Last time we discussed the nutritional values of the two most commonly consumed teas (green & black), but there are more than just two types of tea – teas served at Chinese dim sum house, herbal and fruit teas served in western afternoon tea, and different types of Japanese tea. This issue of “Functional Foods” will illustrate the differences between the above three types of tea in table (Chinese, Western and Japanese), and will continue to explore a few more tea-drinking myths.

Chinese Tea

Chinese teas are mainly made by brewing tea leaves. Tea leaves after harvest will go through a series of processes to become what we see in the pot of the dining table – wither, stir (ferment), stir-fry (high temperature destroys the active enzymes inside the leaves), roll (physical force destroys the tissue and structure of the tea), bake, and dry. Chinese tea can be divided into five main types – non-fermented, mildly-fermented, semi-fermented, fully-fermented and post-fermented. The following table shows the differentiation and examples of different Chinese tea.

Non-fermentedGreen Tea1. Bi-lou-chun
2. Long-jing
3. Huang-shan Mao-feng
Mildly-fermentedWhite Tea1. White peony
2. Shou-mei
Semi-fermentedOolong Tea1. Si-ji-chun
2. Oolong
3. Da Hong Pao
4. Narci-ssus
Fully-fermentedBlack Tea1. Assam
2. Ceylon
3. Dar-jee-ling
Post-fermentedDark Tea1. Pu’er
Fermentation: The process where tea leaves are oxidized by exposing to air, which is key to determine the color, aroma, taste and quality of the tea. Tea during fermentation would produce dark-colored components such as theaflavins (TFs) and thearubigen (TRs), therefore fermented tea is darker than non-fermented tea.

Western Tea

Herbal TeaRoselle, chrysanthemum, rose, ginger, chamomile, nettle root
Fruit TeaApple, lemon, strawberry, raspberry, elderberry
Strictly speaking, it is not tea, and no tea leaves is involved at all.

After harvesting the flowers/fruits, they are processed and dried, which are then brewed in hot water like tea.

Japanese Tea

Non-fermented Japanese Tea

Cut off sunlight about three weeks before harvest. The difference from Gyokuro is that it will be steamed in a baking oven.Like matcha, sunlight will be cut off for three weeks before harvest. Processing afterward is the same as that of sencha.The most common tea in Japan. After tea leaves harvest, it is steamed and stir-fried to inhibit fermentation.Stir-fry the sencha over very high heat until it is brown color, the heating process will produce the aroma of the tea.

Processed Tea

Stir-fry the soaked and steamed brown rice, then mix it with sencha, the genmaicha is the tea of brown rice to sencha ratio 50%:50%.

Without Tea Leaves

Barley Tea
A popular drink in Japanese households. Barley seeds are heated, fried, and brewed with hot or cold water.

Myths about tea-drinking

1. Is the currently popular decaffeinated tea more beneficial?
Most of the decaffeinated teas on the market are herbal teas. Strictly speaking, herbal teas are not “teas”, because they are only brewed from dried flowers without tea leaves, and are named simply because they are brewed like teas. Herbal teas have a wide variety and each herbal tea has its own particular nutritional value.
People who need to be cautious of caffeine intake, such as children are advised to have no more than 5 mg per kg of body weight per day and pregnant women with no more than 200-300 mg per day, may consider drinking decaffeinated tea.  According to the Center for Food Safety, the intake of coffee (200 mg caffeine/1 cup), milk tea (170 mg caffeine/1 cup) and other caffeine-containing beverages are generally safe for most of the healthy adults, which shall not be a worry to the general public.

2. Does drinking tea promote digestion and increase appetite?
Catechins, tannins and caffeine in tea can stimulate the production of gastric acid, which enhances digestion. Research in Taiwan found that a type of Oolong named “Qing-Xin” is rich in “teaghrelin”, which promotes the sense of huger and peristalsis and results in an increase in appetite.
Warm Reminder: Avoid drinking tea on an empty stomach, which may result in unwell feeling in some people.

3. Is making tea with tea in teabags the same as making tea with just tea leaves?
Not necessarily. According to Greenpeace, many people think that tea bags are made of tea and paper, but in fact most of the tea bags on the market are made of plastic – polypropylene (PP). A study by McGill University in Canada pointed out that when plastic tea bags are brewed in boiling water, one of the samples released more than 11.6 billion micro-plastics, which is thousands of times higher than other food in related studies. In addition, the metal stapler pins on the tea bags may also release heavy metals after high temperature and prolonged brewing.
It is recommended to buy brands that are made of non-plastic materials (Plastic-Free Tea Bags) and tea bags without metal stapler pin.

American Journal of Clinical Nutrition Vol.93, American Medical Association, Asia Pacific Journal of Clinical Nutrition, PMID: 9518397, 10584049, 10823400, 11527506, 12428980, 12439647, 14519830, 14519829, 15548944, 15548939, 16311246, 17013636, 18842784, 19308337, 21477653, 27854314, Stroke Vol. 52