First, according to the different picking places of bird's nest, it can be divided into Dongyan and Wuyan Dongyan. Dongyan is a bird's nest picked in wild caves and coastal cliffs, which is the most primitive form of bird's nest. Dongyan is gray or yellow, with many feathers and impurities, and its taste is refreshing. Due to the early exploitation, the living environment of Jin Siyan was destroyed, and the yield of Dongyan decreased year by year, and the yield of Dongyan was low. With the growing voice of environmental protection, people are actively changing the living environment and bird's nest picking environment in Jin Siyan. Subsequently, Dongyan was gradually replaced by domestic swallow. In Jin Siyan, the environment for choosing domestic swallows has changed from caves and cliffs to artificial houses suitable for nesting, without changing the living habits of Jin Siyan. The combination of natural virgin forest environment and artificial shed technology has effectively solved the contradiction between Jin Siyan protection and bird's nest production, and formed a unique original ecological shed swallow, which is white, loose, hairy, smooth and soft. If the sanitary conditions of the swallow house are well controlled, the bird's nest in the house will be cleaner and the color will be ideal, while the bird's nest in the cave may contain more materials such as sand and soil. Secondly, judging from the color of bird's nest, Bai Yan's, Huang Yan's and Xueyan's bird's nests were formed by the saliva secreted by the mucus glands with developed throat in Jin Siyan, which condensed into solids in the air. It is a white bird's nest built by digestive insects, algae and whitebait ingested by Jin Siyan, so it is called Bai Yan, also known as Yan Guan. The whole bird's nest is relatively white, and naturally it is white with a little yellow. Yan Huang: The whole bird's nest or most of it is yellow, which is a natural phenomenon. Some bird's nests picked from caves also show uneven brownish red, blood red, brown or brownish yellow, with deep bottom and shallow middle and edges. It needs to be clarified that this color does not come from the blood in the swallow's mouth. The reason for its formation is mainly considered to be the result of the interaction of the environment in which the bird's nest is located, such as air, humidity and rocks. Especially from the living environment of swallows and the infiltration of high-iron substances into bird's nest through the nest wall. This part of bird's nest is called blood swallow. It is generally believed that blood swallow is rich in minerals, and its nutritional value is higher than that of Bai Yan, but not all minerals are necessarily beneficial to human body. Thirdly, according to the production forms of bird's nest, it is divided into Mao Yan and Mao Yan, Cao Yan. Mao Yan's name is because the bird's nest has not been processed or treated, showing a shape mixed with some swallows' hair. Mao Yan is mainly processed into Zhan Yan, Yantiao and Yanjiao. Grass swallows are mainly nylon grass, and edible bird's nest has many impurities and rough taste. Grass swallows are mainly processed into broken swallows and cakes. Four, according to the sales form of bird's nest, can be divided into bird's nest, bird's nest, bird's nest, bird's nest. After washing, selecting, shaping and drying, the bird's nest has few impurities, which can meet the standard of normal stewing and basically maintain the original shape of bird's nest. Because there is no uniform standard in the bird's nest industry, different merchants divide swallows into different grades according to their quality, such as Longya, Longtou, First-class Swallows, Second-class Swallows, A-class Swallows and Official Swallows. Some strips, blocks, cakes and horns of Yan are formed in the process of cleaning, picking, shaping or processing, and their nutritional value is equivalent to that of Yan. Some of them are made after grass swallows are processed. Its nutritional value is equivalent to that of Zhan Yan, but its appearance is different. 5. According to the collection season, the collection season of bird's nest is generally from February to 10 every year. The bird's nest harvested in February-April is suitable for insect reproduction because of abundant rain, while Jin Siyan has plenty of food and much saliva secretion, so the bird's nest cup is complete, shiny and hairless, so we often call it the "first swallow". The bird's nest collected from May to 65438+ 10 is called "Phase II Swallow" and "Phase III Swallow", which is the molting period in Jin Siyan, so the nest is loose, its light shape is not as good as that of Phase I, and there are many fluff impurities.