Shape and volume: the best bird' s nests is in the shape of a boat or spoon. Bird' s nest can be triangular in shape if they have been built in the corner of two adjacent walls. However for nutritional value the shape does not matter. Bird' s nests that are broader in width rank higher. The real bird' s nest should be in a natural shape.

# Color and Purity: The best bird' s nest should be of natural colour, containing no mud and other impurities like moss. The colour of the white nest is an actual ivory. The yellow nest and the bloodyred nest are coloured straw and red, respectively. The variations and intensity in the colour are due to the difference in the mineral constituents of the food the swallow ate. The bird' s nests, regardless of their colour, swell when soaked in clear water. The colouration in the bird' s nest will fade and the nest threads look transparent after swelling. However, the water used for soaking should still remain transparent and colourless.

# Density and Swelling Capacity: Bird' s nests that have finer and denser nest threads appear almost gapless. They are bigger and thicker in volume and should have a higher swelling capacity. The swelling capacity refers to the water holding ability of a bird' s nest. The higher the swelling capacity, the greater the bird' s nest distends after immersion in water. Bird' s nests of different categories show different magnitudes of swelling capacity, i. e. the ratio between the weight of the bird' s nest before and after swelling can be different. The swelling capacity should be measured by weight instead of by volume.

# Flavor and Dryness: Bird' s nest should be selected by smell. A real bird' s nest retains a little bit of a fishy smell of the swallow' s saliva. When cooked, it releases a light aroma resembling the aroma of an egg white. It is essential to select a dry bird' s nest. A bird' s nest that is sticky and soft is certainly not dry enough. A wet bird' s nest weighs heavier thus the price will be overcharged from the extra weight. A wet bird' s nest would not be convenient for storage as it would attract mould easily and has a low swelling capacity.