There are two methods to identify tea: sensory identification and physical and chemical identification. Sensory identification, also called evaluation, the first shape belongs to appearance identification. Sensory identification can be divided into four items: first, different types of ropes require different rope presentation methods, such as tightness, straightness, thickness, oblateness, total breakage, light weight and so on. It should be in line with the normal situation of this variety. Second, the color, whether dull or shiny, should also meet the requirements of varieties, such as red-brown black tea, brand-new green tea, brown-green scented tea and so on. The third is cleanliness, which should be clean and stalk-free, and the pieces, pieces and powder should not exceed the standard, and should not contain non-tea inclusions. The fourth is tenderness. For the same variety of tea, it is better to have more white buds. Although the rope is a little thick, it is tender and bright.
Identification of the endoplasm of tea can be divided into aroma, taste, soup color and leaf bottom. First, aroma, fresh nose, strong and pure, light and impure, stuffy and astringent, and smelly. All kinds of scented tea should have their own unique normal aroma. For example, jasmine tea should have jasmine fragrance, and magnolia and Zhu Lan scented tea should have magnolia and Zhu Lanxiang. The second is taste. Taste buds with tongue feel mellow and fresh, the best, followed by astringent, bitter, rough and weak fermentation, and moldy, spicy and raw grass are the worst. The third is the color of the soup. When the tea is hot, observe the depth of light and shade. Generally speaking, shade is appropriate, but the color of black tea soup is darker than that of green tea, and the pressed tea soup is darker. Fourth, at the bottom of the leaf, taste the brewed wet tea and press it by hand. Soft and elastic belong to delicate, hard and inelastic belong to thick and old. The above identification methods mainly distinguish between superior, inferior and inferior. Everything is from quantitative change to qualitative change, and fake and shoddy tea is often found in this sensory identification.
There is no comprehensive quality standard for tea, and the whole process is expressed in words. At present, there are only the standards for purchasing raw tea at the place of origin, that is, Grade 6 18 and the international GB/T9 172- 1988 standard for scented tea parisons. Only the national standard GB9679- 1988 "Hygienic Standard for Tea" is mandatory. Sensory index: it has the normal appearance, inherent color and fragrance of this tea, and cannot be doped with exotic plants. Leaves shall not contain grass substances, and shall not have peculiar smell, bad smell or musty smell. Physical and chemical indexes: the content of lead (3mg for pressed tea), copper 60mg and antimony 0.2mg (0.4mg for pressed tea) per kilogram.
The pesticide residue index of organochlorine and organomercury, HCH and DDT shall not exceed 0.2mg/kg.
Moisture index: the higher the water content, the faster the deterioration of tea; The less moisture, the less likely it is for tea to deteriorate, but if the moisture is too low, the quality of tea will decline. Generally, the water content of tea leaves is about 3%.
Ash index: Inorganic compounds in tea are called ash, and the content of phosphorus and potassium in ash is the highest, followed by calcium, magnesium, iron, manganese, aluminum and sulfur, and the total amount shall not exceed 7%.
Physical and chemical identification of tea can be divided into physical identification and chemical identification.
The physical identification of tea has four contents:
1 leaf inspection: take a little boiled water and observe it with a magnifying glass. If the leaf color is dark green, the top is smooth, the back is fluffy, the leaf is oval, the tip is short and blunt, the leaf edge is serrated, and there are cilia on the serrations, it can be judged as true tea. Leaves that do not meet the above characteristics are adulterated tea.
2. Inspection of soaked tea leaves: take suspicious tea leaves, make them into powder, put them in a watch mirror, cover them with the watch mirror, control the electric furnace, bake them with low fire for 5 ~ 10 min, and inspect them under the microscope on the covered watch mirror. If you can see many tiny oil droplets, many tiny needle-like crystals are caffeine, which means pure tea. Otherwise, it means that caffeine has dissolved and can be judged as brewed tea. It can also be determined according to the specific gravity method. The specific gravity of soaked tea extract is 1.0023 ~ 1.0057, which is far from that of fresh tea extract1.0098 ~1.05438+045. The combination of the above two methods can make a more accurate judgment.
3. Inspection of tea with pigment: put tea powder on white paper and rub it repeatedly. If there are stripes of various colors on the paper, it means there are colorants. You can also add a little chloroform to your tea. After shaking, if chloroform is blue or green, it means that the tea leaves are doped with colorants such as indigo or turmeric.
Waxing test of tea: spread a little tea on rough white paper and iron it with an electric iron. If there are obvious oil stains on the white paper, it means that beeswax or paraffin has been added to the tea.
Chemical identification of tea;
If the suspicious leaf does not contain caffeine and manganese, it can be proved that it is not tea, but if caffeine and manganese are detected, it is not certain that the suspicious leaf is tea. Therefore, it is necessary to detect the presence or absence of theanine in accordance with the national standards, so as to finally determine the authenticity of tea.
Market spot checks found that bulk tea generally does not match the quality and price, and the quality and price are high; In the packaging of tea, many unscrupulous traders forged brand-name trademarks and packaging such as "Monkey King" and "Jinghua", so as to confuse the fake with the real, shoddy and short of two. Take "Jinghua" brand as an example, its trademark, longevity pattern and packaging bag pattern have all been registered and protected by national laws. Packaging fixed-point printing, meticulous and exquisite, consumers should carefully identify when buying packaged tea, pay attention to comparison, and avoid being fooled.
1999 the results of national quality supervision and spot check of jasmine tea in the fourth quarter showed that pesticide residues exceeded the standard, accounting for 4.29%. Tea in China has a vast area and a wide variety, and most tea gardens are located on high mountains, with pure soil and water and little pollution. However, there are many pests and diseases in tea gardens in hilly areas in summer and autumn, and tea farmers ignore the correct use of pesticides, resulting in excessive pesticide residues in tea. In the process of tea processing and blending, raw materials are mixed with each other, which expands the scope of pesticide residue pollution and seriously affects the reputation, domestic sales and foreign trade export of tea. The new inspection standard implemented by the European Union since July 2000 1 has greatly reduced the pesticide residue limit index of tea. As a big country in tea production and export, China is facing severe challenges, and Beijing, Tianjin and Shanghai have formulated strict tea quality standards.