title: Edible bird's nests--how do the red ones get red?
abstract: BACKGROUND
  Red edible bird's nests are regarded as of higher beneficial value for health and hence fetch a higher price than the white ones. Their red colour remains a myth.
  
  
  OBJECTIVE
  To determine if white edible bird's nests can turn red by vapours generated from sodium nitrite in acidic conditions and by vapours from 'bird soil'.
  
  
  METHODS
  White edible bird's nests were exposed to vapours from sodium nitrite dissolved in 2% HCl or from 'bird soil' in hot and humid conditions.
  
  
  CONCLUSIONS
  Vapours from sodium nitrite dissolved in 2% HCl or from 'bird soil' containing guano droppings from swiftlet houses were able to turn white edible bird's nests red. The reddening agent in 'bird soil' was water-soluble and heat-stable. The red colour of edible bird's nests is likely caused by the environmental factors in cave interiors and swiftlet houses.
authors.affiliation: School of Life Sciences, The Chinese University of Hong Kong, Tai Po Road, Shatin, N.T., Hong Kong, PR China. paulbut@hotmail.com
authors.forename: Paul Pui-Hay
authors.initials: PP
authors.lastname: But
authors.forename: Ren-Wang
authors.initials: RW
authors.lastname: Jiang
authors.forename: Pang-Chui
authors.initials: PC
authors.lastname: Shaw
mesh_terms: D000818:Animals; D001717:Birds; D003116:Color; D004777:Environment; D006799:Housing, Animal; D008516:Medicine, Chinese Traditional; D012977:Sodium Nitrite / Q000737:chemistry
chemical_list: D012977:Sodium Nitrite