In fact, this statement has no scientific basis, because secondary amines are widely found in many foods, especially in pickled products. Take bread as an example, it generally contains 2mg/kg of secondary amine. For example, if bread is the staple food, the daily intake of secondary amine from bread is 1- 1.5 mg.
When people drink tea, the only secondary amine they get from tea is bread? 0, can be ignored. Moreover, secondary amines themselves are not carcinogens, and nitrates must exist to form nitrosamines, which can only cause cancer if they reach a certain order of magnitude. Drinking tea can get more tea polyphenols and vitamin C from tea, which can effectively prevent the synthesis of nitrosamines in human body and is a natural inhibitor of nitrosamines. Therefore, drinking tea or overnight tea will not cause cancer.
However, from the point of view of nutrition and hygiene, tea soup is exposed to the air for a long time, which is easy to breed corrupt microorganisms and make tea soup rancid.
In addition, the tea soup is put for a long time, and the nutrients such as tea polyphenols and vitamin C are easy to be oxidized and reduced. Therefore, although overnight tea is harmless, it is generally better to drink it with the bubble.
Overnight tea is rich in alcohol and fluoride, which can prevent capillary bleeding. If you have oral bleeding, skin bleeding, ulcers and abscesses, you can use it to treat them. If the problem is the nose and mouth, you can wash your hands, rinse your mouth or drink it with overnight tea.
People with skin diseases can wash it, and those with red eyes or tears of unknown reasons can wash it with overnight tea, which has a good effect. Rinsing a few mouthfuls of overnight tea after brushing your teeth in the morning or before eating can not only make your mouth fresh and refreshing, but also strengthen your teeth. Some traditional Chinese medicines for treating rhinitis are also made of overnight tea.
The quality of tea is mainly identified from four aspects: color, fragrance, taste and shape, but for ordinary tea drinkers, when buying tea, they can only look at the shape and color of dry tea and smell the fragrance of dry tea, which increases the difficulty of judging the quality of tea. The following is a rough introduction to the method of identifying dry tea from five aspects: tenderness, skewness, color, fragmentation and purity.
1, tenderness: tenderness is the basic factor that determines quality. The so-called "dry appearance, wet ass" means tenderness. Generally, tea with good tenderness is easy to meet the appearance requirements of this kind of tea (such as "light, flat, flat and straight" in Longjing). In addition, it can also be identified from the presence or absence of tea seedlings. Good pre-seedlings and white hair shows show that they are tender and well-made. If the tenderness of raw materials is poor, no matter how good the workmanship is, there will be no white hairs on the sharp seedlings and tea strips. But tenderness can't be judged only by the number of fine hairs, because the specific requirements of various teas are different. For example, the high-quality Lion Peak Longjing is fluff-free. Moreover, fuzz is easy to fake and operate by hand. The tenderness of bud leaves is judged by fluff, which is only applicable to "fluff" teas such as Mao Feng, Maojian and Yinzhen. What needs to be mentioned here is that the most tender fresh leaves should also show a bud and a leaf, and it is not advisable to pick buds unilaterally. Because the bud nucleus is an imperfect part, its content is not comprehensive, especially the chlorophyll content is very low. Therefore, tea should not only be made into buds in pursuit of tenderness.
2. Cord: Cord is a certain shape and specification of various tea sets, such as fried green ribbon, round pearl tea, flat longjing tea, granular red broken tea and so on. Generally, long strip tea is elastic, straight, strong, thin, round, flat, light and heavy; Round tea depends on the elasticity, uniformity, weight and ethereal degree of particles; Flat tea to see if it is smooth and meets the specifications. Generally speaking, the rope is tight, heavy, round (except flat tea) and straight, indicating that the raw materials are tender, the workmanship is good and the quality is excellent; If the appearance is loose, flat (except flat tea), broken, smoky and burnt, it means that the raw materials are old, the workmanship is poor and the quality is poor.
Take the standard of Hangzhou green tea as an example: first-class, second-class, third-class, fourth-class, fifth-class, sixth-class, fine-grained, tight-grained, fine-grained, still tight-grained and slightly loose-grained. It can be seen that tight, solid and sharp seedlings are the best.
3. Color: The color of tea is closely related to the tenderness of raw materials and processing technology.
All kinds of tea have certain color requirements, such as black tea, green tea, oolong tea and black tea. However, no matter what kind of tea, good tea requires consistent color, bright luster, oily and fresh. If the colors are different, the shades are different and dull, it means that the raw materials are old and tender, the workmanship is poor and the quality is poor. The color of tea also has a great relationship with the origin and season of tea trees. Such as alpine green tea, the color is green and yellowish, fresh and bright; Low camellia or flat tea is dark green and shiny. In the process of making tea, due to improper technology, the color often deteriorates.
When buying tea, you should judge according to the specific tea you buy. For example, Longjing, the best Shifeng Longjing, had natural brown rice color and light yellow tea before the Ming Dynasty. This is a major feature of Shifeng Longjing, which is obviously different from other Longjing in color. Because the price of Shifeng Longjing is extremely high, tea farmers will create this color to pretend to be Shifeng Longjing. The method is to fry the tea a little more to make the leaves yellow. The difference between true and false lies in that the real lion peak is symmetrical, bright and clean, light yellow and light green, with a faint fragrance in the tea fragrance; The fake lion peak angle is loose and empty, the hair is rough and yellow, and the tea smells like fried soybeans. It's really hard to judge without many comparisons. But once brewed, the difference is very obvious. The over-fried fake lion peak is not as rich and tender as Longjing.
4. Whole crushing: Whole crushing refers to the shape and crushing degree of tea, with flattening as the best and crushing as the second. The standard tea tasting is to put the tea in a plate (usually made of wood), so that the tea can be layered in turn according to its shape, size, weight, thickness and crushing degree under the action of rotating force. Among them, the thick ones are at the top, the tight ones are concentrated in the middle, and the broken ones are deposited at the bottom. All kinds of tea, medium-grade tea is the best. The upper layer is generally thick and old leaves, with light taste and light water color; There are many broken teas at the lower level, and the taste is often too strong after brewing, and the soup is darker.
5. Cleanliness: mainly depends on whether the tea leaves are mixed with camellia seeds. , tea stems, tea powder and tea seeds, and the amount of inclusions such as bamboo chips, sawdust, lime and sand mixed in the production process.
Tea with good purity does not contain any inclusions. In addition, it can also be identified by the dry aroma of tea. No matter what kind of tea, there must be no peculiar smell. Every kind of tea has a specific aroma, and the dry aroma and wet aroma are also different, depending on the specific situation. Green gas, burnt smoke and cooked stuffy smell are not desirable. The above is just a general identification method. It is the taste, aroma and color of tea soup that are the easiest to identify the quality of tea. So if you can, try making tea. If you have a special preference for a certain kind of tea, you'd better look up some information about this kind of tea, accurately understand its color, fragrance and shape characteristics, and compare the tea you buy every time. The more times, the easier it is to get to the point.