In the past, there was a saying that overnight tea should not be drunk as it might lead to cancer. The reason is that overnight tea contains secondary amines that can be converted into carcinogens nitrosamines.
In fact, this statement has no scientific basis, because secondary amines are widely present in a variety of foods, especially in pickled products. Take bread, which usually contains 2mg/kg. Secondary amines, such as bread as the staple food, the secondary amines consumed from bread every day are 1-1.5mg.
And by drinking tea, the secondary amines ingested by people from tea are only ?0 of the staple food bread, which can be seen to be insignificant. Moreover, secondary amines themselves are not carcinogens. Nitrates must be present to form nitrosamines and reach a certain order of magnitude to have carcinogenic effects. Drinking tea can obtain more tea polyphenols and vitamin C from tea leaves. They can effectively prevent the synthesis of nitrosamines in the human body and are natural inhibitors of nitrosamines. Therefore, drinking tea or overnight tea does not cause cancer.
However, from a nutritional and hygienic perspective, when the tea soup is exposed to the air, it is easy to breed putrefactive microorganisms after being left for a long time, causing the tea soup to go rancid and deteriorate.
In addition, if the tea soup is stored for a long time, nutrients such as tea polyphenols and vitamin C are easily oxidized and reduced. Therefore, although overnight tea is harmless, it is generally better to drink it as you brew it.
Overnight tea is rich in alcohol and fluorine, which can prevent capillary bleeding. If you suffer from oral bleeding, skin bleeding, sores, abscesses and other problems, it can be used to treat it. If the problem is in the mouth and nose, you can use overnight tea to wash, gargle or drink.
If you have skin disease, you can wash your eyes. If your eyes have red streaks or unexplained tears, you can wash your eyes with overnight tea, which is effective. Swish a few sips of overnight tea after brushing your teeth in the morning or before eating or drinking. It can not only make your mouth fresh and refreshing, but also strengthen your teeth. Some Chinese medicines for treating rhinitis are also made from overnight tea.
The quality of tea is mainly identified from four aspects: color, aroma, taste and shape. However, for ordinary tea drinkers, when buying tea, they can generally only look at the appearance and color of dry tea, and smell it. The dry aroma makes it more difficult to judge the quality of tea. The following is a rough introduction to the method of identifying dry tea from five aspects: tenderness, cord, color, wholeness and clarity.
1. Tenderness: Tenderness is the basic factor that determines quality. The so-called "look at the shape when dry and the bottom of the leaf when wet" refers to tenderness. Generally, tea leaves with good tenderness can easily meet the appearance requirements of the tea type (such as "light, flat, flat, straight" in Longjing). In addition, it can also be identified based on the presence or absence of front seedlings in the tea leaves. The front shoots are good and the pekoe is exposed, which means the tenderness is good and the workmanship is good. If the tenderness of the raw materials is poor, no matter how good the workmanship is, the tea sticks will not have front sprouts and pekoe. However, the tenderness cannot be judged only by the amount of hair, because the specific requirements of various teas are different. For example, the excellent Shifeng Longjing has no hair on the body surface. Furthermore, the hair is easy to fake, and many are artificially made. The tenderness of buds and leaves is judged based on the number of hairs, which is only suitable for "fluffy" teas such as Maofeng, Maojian, and Yinzhen. What needs to be mentioned here is that the most tender leaves have to be buds and leaves. It is inappropriate to pick the buds one-sidedly. Because the bud core is an imperfectly grown part, it contains incomplete ingredients, especially the chlorophyll content is very low. Therefore, tea should not be made from the heart of the bud simply for the sake of tenderness.
2. Bars: Bars are certain shape specifications of various types of tea, such as fried green strips, pearl tea round, Longjing flat, black broken tea granules, etc. Generally, for long-shaped tea, look at the tightness, straightness, strength, thinness, roundness and weight; for round tea, look at the tightness, uniformity, weight and emptyness of the particles; for flat tea, look at the smoothness and whether it meets the specifications. Generally speaking, if the rope is tight, the body is heavy, round (except for flat tea) and straight, it means the raw materials are tender, the workmanship is good, and the quality is high; if the shape is loose, flat (except for flat tea), broken, and there is smoke and burnt The smell indicates old raw materials, poor workmanship and poor quality.
Take the green tea cord standards in Hangzhou as an example: Grade 1 Grade 2 Grade 3 Grade 4 Grade 5 Grade 6 Thin and tight with front seedlings Tight and thin Still with front seedlings Still firm Still tight Slightly loose Roughly loose. It can be seen that tightness, solidity, and front seedlings are the best.
3. Color: The color of tea is closely related to the tenderness of raw materials and processing technology.
Various types of tea have certain color requirements, such as black tea and oily black, green tea and emerald green, oolong tea and dark brown, black tea and black and oily color, etc.
However, no matter what kind of tea, good tea requires consistent color, bright luster, oil and freshness. If the color is different, different shades, dark and dull, it means that the raw materials are old and tender, poor workmanship and poor quality. The color of tea leaves also has a lot to do with the origin and season of the tea tree. For example, high mountain green tea has a green and slightly yellow color, fresh and bright; low mountain tea or flat tea has a dark green and shiny color. In the process of making tea, the color often deteriorates due to improper techniques.
When purchasing tea, you should make a judgment based on the specific type of tea purchased. For example, in Longjing, the best Shifeng Longjing, the Mingqian tea is not emerald green, but has a natural brown beige color, which is bright yellow. This is a major feature of Shifeng Longjing, which is obviously different from other Longjings in color. Because the price of Shifeng Longjing is so high, tea farmers will create this color to pass it off as Shifeng Longjing. The method is to slightly over-fry the tea leaves during the frying process to cause the leaves to turn yellow. The difference between real and fake ones is that the real Shifeng is well-proportioned and smooth, light yellow and tender green, with a fragrance of tea; the fake one is pine and hollow, rough, yellowish, with the fragrance of tea and roasted soybeans. It is indeed not easy to judge without multiple comparisons. But once brewed, the difference is very obvious. The over-cooked fake Shifeng does not have the rich and tender fragrance that Longjing should have.
4. Whole and broken: Whole and broken refers to the shape and degree of brokenness of the tea leaves. Evenness is better and brokenness is the second. A relatively standard tea review is to place the tea leaves on a plate (usually wooden), so that under the action of rotating force, the tea leaves form orderly layers according to shape, size, weight, thickness, and shredding. Among them, the thick ones are in the uppermost layer, the compact and heavy ones are concentrated in the middle layer, and the broken and fine ones are deposited in the bottom layer. For all types of tea, it is better to have more tea in the middle layer. The upper layer generally contains more thick and old leaves, with a lighter taste and lighter water color; the lower layer has more broken tea, which often tastes too strong and the soup is darker after brewing.
5. Clarity: It mainly depends on whether the tea leaves are mixed with tea flakes, tea stems, tea powder, tea seeds and the amount of bamboo chips, wood chips, lime, silt and other inclusions mixed in during 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 should be no peculiar smell. Each type of tea has a specific aroma, and the dry aroma and wet aroma are also different, which need to be determined according to the specific situation. Green aroma, smoky aroma, and cooked and stuffy aroma are all undesirable. The above are just general identification methods, and the easiest way to judge the quality of tea is the taste, aroma and color of the leaf tea soup after brewing. So if possible, when buying tea, try to brew it and try it. If you particularly prefer a certain kind of tea, it is best to look up some information about the tea to accurately understand the characteristics of its color, flavor, shape, and compare the teas you buy with each other. The more times you do it, the easier it will be to grasp the key points.