The results of experiments testing the effects of yeasts, sunlight, and temperature on the food dyes tartrazine, ponceau 4R, indigotin and azorubin (used for colouring ginger soft drink) are reported. Light was found to exert a greater influence than heat, and yeasts growth hastened colour degradation. Yeasts assimilated to varying extent the colouring compounds and, when failing to do it, showed a certain power of adsorption by the no longer viable cells.
