Chemical receptors stimulate the taste receptors on the tongue to register a reaction. With smell, the chemicals stimulate the receptors on tissues in the nasal cavity. While all these factors influence flavour, little experimental work has been done with infants beyond the influence of taste. Tastes include sweet, sour, bitter, salty and perhaps a fifth which is the taste of umami or monosodium glutamate. Sweet is detected on the tip of the tongue, bitter at the back, salty on the side of the tongue near the front and sour is detected on the side of the tongue near the back.
Tastes develop in infants over time.
The ability to detect sweet tastes occurs before birth. Within days of birth, infants can detect dilute sweet solutions and differentiate different sugars. They prefer very sweet sugars such as sucrose and fructose to mildly sweet tastes such as glucose and lactose. The ability to detect salt develops postnatally. Experience with salty tastes does not appear to be a factor in acceptance of salt at this later age, nor does it appear to be a learned response.