Bird's nests can be divided into three categories according to different colors, namely white swallow, yellow swallow and red swallow.
First, the white swallow
The nest color of the nest that the swiftlet has just built is generally whiter, called the white swallow. The "Guan Yan" enshrined to the dignitaries in ancient times refers to the complete, clean and high-quality white swallow, which is generally the nest built for the first time by the swiftlet, which is completely condensed from the mucus secreted by the throat, the texture is pure, the quality is the best, and it is known as the best in the bird's nest.
2. Huang Yan
The nest of the swiftlet will appear different colors over time due to changes in the environment of the nesting place, such as air temperature and humidity. Bird's nest has existed for a long time, affected by natural oxidation, the color will slowly change from pearl white (white swallow) to pearl yellow (yellow swallow), just like peeled pears, after contact with oxygen, it will turn yellow after a long time.
3. Blood Swallow
The real blood swallow actually does not exist, what we usually call "blood swallow" is actually a red swallow, which is formed by the long-term penetration and oxidation of the minerals in the cave, not the result of the swiftlet vomiting blood, if it is really hemoglobin is oxidized, it will only form black-brown methemoglobin. Due to the different minerals and the length of time, the color of the red swallow is also different, from gray yellow to earth yellow and tan. Bird's nest is not picked for a long time, and under some temperature and humidity, after the action of microorganisms and oxidation, the color will gradually become darker.
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