1. Guanyan belongs to the top grade. It is called the official swallow because it used to pay tribute only to the official. It has less impurities and a slightly yellow and bright color. It looks like a loofah sponge. After adding water, it softens and expands about 7-8 times, which is called "hair head";
2. Mao Yan is second, with more impurities than Yan Guan, deeper color and brightness, poorer "hair" and slightly lower value and price;
3. Grass swallows are the lowest of the above three categories, and most of them are the second nesting of swallows after the bird's nest is picked. They contain more impurities and need to be rinsed to remove impurities, and the price is also the cheapest.
There is a red substance oozing from the attached red rock wall in the bird's nest, and the whole body is dark red, called "blood swallow" or "red swallow", which is a rare treasure in bird's nest. However, a few bird's nests are bloodshot or caused by the second nesting of swallows, so the natural blood swallows are scarce.
Extended data:
Tips for purchasing bird's nest: it is appropriate to identify bird's nest by looking, touching, smelling water and fire.
1, look: the first-class product is bright, with less down, neat periphery, melon collaterals and bird's nest feet at both ends;
2, feel: good bird's nest is dry and elastic, wet and heavy, soft but not dull;
3, smell: dried bird's nest has a musty smell, and stewed bird's nest is like peeling the protein taste of cooked eggs;
4, fire and water identification: a good bird's nest has a "hair head" after soaking in water, which can expand 7~8 times, and it is fake when it becomes hard or faded after soaking in water;
5, burning bird's nest, such as burning hair, such as smoking, may be plastic.
When buying, we should distinguish between "dyed bird's nest", "added bird's nest (with cassava powder and fish powder)" and "completely fake bird's nest (with resin, plastic and bleached seaweed)".
Baidu encyclopedia-bird's nest (traditional food)
People's Network-Tips for Quickly Distinguishing True and False Bird's Nest