Flavor comes from the combination of odor and taste information. Taste information comes from taste buds that detect five different taste dimensions — sweetness, saltiness, bitterness, sourness, and umami, also known as savoriness. A newborn responds to all of these taste dimensions except saltiness. Infants younger than 4 months display little preference for water or salt solutions. In contrast, babies from age 4 to 24 months prefer salty water, while children from age 2½ to 5 years old prefer pure water over saline.7 Researchers believe that the salt taste receptors simply have not matured before 4 months of age.
The Newborn Senses: Taste & Smell
Newborns outperform adults at a variety of smell tests. For example, newborns detect odor components in human sweat better than adults do.1 Other research has shown that babies recognize the smell of amniotic fluid and prefer to nurse from a breast that has been moistened with their own amniotic fluid.2 In a different study, newborns (sometimes just hours old) were allowed to smell different samples of breastmilk. Some samples came from their own mothers and other samples came from different nursing mothers. The babies tried to suck and nurse more in response to their own mothers’ odors. Just as interesting, the babies who had more than 50 minutes of skin-to-skin contact were better at recognizing their mother’s milk than babies who had less skin contact.3 Finally, the scent of breast milk seems to have a calming, painkilling effect on newborns. However, this only worked if the breast milk came from their own mother.4
How exactly does an infant process odors? When researchers presented newborns between 1 and 6 days old with unfamiliar odors, the odors activated the same regions of the brain that are active in adults.5
As for the other flavors, newborns react negatively to most bitter substances, and will also pull away and grimace when given a sour substance.8 In contrast, newborns particularly enjoy sweet things. In fact, when babies drink sugar water immediately before a painful procedure, such as a heel prick or circumcision, they cry less. Newborns also appear to enjoy the savory taste.9 Both of these flavors are readily found in breastmilk.
A newborn’s sense of taste has practical consequences. Evidence shows that the flavors in a mother’s diet get passed through the amniotic fluid in utero and the breastmilk after birth. Flavors peak in the breastmilk about 1½ to 3 hours after mothers eat the flavorful foods.10 The earlier the baby gets exposed to a certain flavor, the more accepting they are of that food later when parents introduce solid foods to their children.