Black tea is a red to brown colored hot beverage and is made from the same tea plant as green or white tea. Unlike green tea, the tea leaves are oxidized as part of the black tea manufacturing process.
Production
While respecting certain rest periods, the tea leaves can be harvested or picked throughout the year. For this purpose, the first two leaves and the associated bud of the plant are taken by hand. This is followed by the oxidation process (formerly known as the “fermentation process”), in which the leaves are laid out to wilt for about 16 hours. In this way, water is extracted from the tea leaves, causing them to lose their brittleness. They are then rolled, destroying the cell walls of the leaves. Enzymes can escape, causing a brown-red coloration. With the following drying – enzymes are inactivated and the tea turns black – the process of oxidation is finished. Due to the oxidation reaction, the majority of essential vitamins, minerals, trace elements and secondary plant compounds as well as enzymes are destroyed. Furthermore, the oxidation or withering process leaves behind many polyphenolic substances, which in high concentrations can have a damaging effect on the body.
Ingredients of black tea
Due to the loss of vital substances (micronutrients) during the production process, no significant coverage of the respective daily requirement can be achieved by drinking black tea: black tea contains mainly the minerals potassium as well as fluoride and small amounts of the B vitamins. The tannins – 0.3 grams in a cup of tea – and essential oils cause the smell and the typical tea aroma.
Caffeine
In a glass of black tea (150 ml) is with circa 30-60 mg only half as much caffeine (trimethylxanthine) as in a cup of coffee (50-150 mg caffeine). Therefore, black tea also has a stimulating and slightly diuretic effect on metabolism, circulation and brain and heart activity, but to a lesser extent than coffee. Due to the tannins, the tea caffeine is absorbed more slowly into the bloodstream and the stimulating effect lasts accordingly longer in contrast to coffee. The reason for this is that the caffeine binds to the tannins and is thus gradually released. The half-life of caffeine is given as four to six hours on average. The following is an overview of the caffeine content of various stimulants:
| Luxury food | Caffeine content [mg] |
| Coffee (150 ml) | 50-150 |
| Espresso (50 ml) | 50-150 |
| Black tea (150 ml) | 30-60 |
| Green tea (150 ml) | 40-70 |
| Cola drink (330 ml) | up to 60 |
| Energy drink (250 ml) | 80 |
| Milk chocolate (100 g) | 20 |
| Semi-sweet chocolate (100 g) | 75 |
A daily consumption of 400 mg of caffeine is considered safe for adults by the EFSA (European Food Safety Authority). The upper limit for pregnant women and nursing mothers is 200 mg of caffeine per day. For children and adolescents, an intake of 3 mg caffeine per kg body weight/day is considered safe. In this age group, caffeine is mainly ingested through the consumption of energy drinks.
Tannins
The tannins contained in black tea belong to the group of astringents and therefore exhibit a similar effect in increased concentrations, as a result of high tea consumption. All substances belonging to the astringents react with the protein of the uppermost layers of tissue, compacting them into firm, cohesive membranes. They promote hemostasis and the healing of wounds and inflammations. Accordingly, tannins have a mild antibacterial and analgesic effect. Finally, the tannins of black tea are beneficial to health, have a soothing effect on the gastrointestinal tract and counteract diarrhea. On the other hand, the tannins also have a detrimental effect with their astringent effect. This can lead to a worsened absorption of additionally taken medications or also of vital substances (micronutrients). For example, tannins in high concentrations inhibit the absorption of iron, as this is partially prevented by the solid membranes that are difficult to permeate.Furthermore, tannins impair the availability of dietary iron. One cup of tea can already reduce availability by about half. Consuming black tea in excessive amounts thus increases the risk of iron deficiency symptoms – pale, rough, brittle skin, disturbances in heat regulation and sensitivity to the weather.
Preparation
The stimulating effect is shown by the black tea only if it is left to brew for 2-3 minutes at the most. Then the predominant part of the caffeine passes into the tea infusion. Primarily, within the first two minutes, the caffeine-like substances theobromine and theophylline are released, which cause the stimulating effect. These substances are also used in medicine as medicines. In particular, this is theophylline as a remedy for asthma. The tannins, on the other hand, are not yet released and the effect of the caffeine predominates. If the tea is left to brew for about 4 to 5 minutes, it loses its stimulating effect and then has a more calming effect on the body. After such a long brewing time, the tannins can be increasingly released from the tea leaves, which then give the black tea a bitter taste. If the tea is left to steep for longer than 5 minutes, too many tannins will pass into the tea infusion – the tea will taste extremely tart and bitter.
Effects on the body
A meta-analysis showed that long-term consumption, i.e. ≥ 12 weeks, of green and black tea leads to a significant reduction in both systolic and diastolic blood pressure. Furthermore, regular consumption of black tea leads to a reduction in serum LDL cholesterol concentration. This effect was most evident in individuals with increased cardiovascular (affecting the heart and vascular system) risk. If black tea is consumed in excessive amounts, it may cause minor headaches, poor performance, and sleep disturbances. In individuals sensitive to the stomach, black tea may irritate the gastric mucosa and cause pain. Unlike coffee, black tea does not stimulate acid secretion in the stomach and, due to the absence of diterpenes, which are components of the oils in coffee, does not affect cholesterol levels, which explains its better tolerance. Excessive consumption of black tea leads to a deficiency of:
- Vitamin C
- Vitamin B6
- Calcium
- Iron
If, in addition to the caffeine in the form of coffee or black tea, alcohol or tobacco is consumed, respectively, the health impairments as well as the symptoms of disease intensify and there is an additive effect. The body is confronted with several toxic substances at the same time and does not have sufficient defense mechanisms – due to the constant degradation – to eliminate the toxic substances.
