House swiftlets produce bird’s nest in a controlled environment, whereby the bird’s nest are formed in a clean and unpolluted environments. The farmers harvest the house bird’s nest regularly, thereby ensuring that the bird’s nest is freshest.
In comparison, the cave swiftlets form nests in the caves, which are dirtier due to the uncontrolled environments being exposed to more foreign materials. The harvesting of cave bird’s nest is not done periodically by the climbers due to the difficulties in accessing the caves for harvesting. Regardless of whether the nests are fresh with infant swiftlets still around or old and contaminated, the climbers will generally harvest all of them.
Bird’s nest colour may differ depending on which area the swiftlets come from. Minor variance in colour may happen, sometimes whitish, other times yellowish. Bird’s nest contains minerals like iron, copper, sodium, and potassium. When the minerals are oxidized, a colour change in the bird’s nest will occur.