Premastication

Premastication, pre-chewing, or kiss feeding is the act of chewing food for the purpose of physically breaking it down in order to feed another that is incapable of masticating the food by themselves. This is often done by the mother or relatives of a baby to produce baby food capable of being consumed by the child during the weaning process. The chewed food in the form of a bolus is transferred from the mouth of one individual to another, either directly mouth-to-mouth, via utensils, hands, or is further cooked or processed prior to feeding.

The behaviour was common throughout human history and societies and observed in non-human animals. While premastication is less common in present-day Western societies it was commonly practiced, and is still done in more traditional cultures. Although the health benefits of premastication are still being actively studied, the practice appears to confer certain nutritional and immunological benefits to the infant, provided that the caretaker is in good health and not infected by pathogens.

Premastication and mouth-to-mouth feeding in humans is postulated to have evolved from the regurgitation of food from parent to offspring or male to female (courtship feeding) and has been observed in numerous mammals and animals of other species. For instance, food begging behaviour observed in young wolves, wild dogs and certain gulls species, which involves the young approaching the beak or mouth of the adult with their own whereupon gaping their mouths or nuzzling, the adult would regurgitate portions of food to feed the young. However, in the aforementioned animals, this nuzzling behaviour and other types of mouth-to-mouth contact are also used for bonding, socialization, and courtship.

Young orangutans also beg for food by such contact and accordingly their caretakers regurgitate to feed them. Indeed, behaviours of mouth to mouth feeding of premasticated food and ritualized mouth to mouth contact for bonding has been observed in anthropoid great apes such as gorillas, orangutans, and chimpanzees. All of this supports the idea that human behaviours of kissing and feeding of premastication foods, either directly or indirectly from the mouth, have their behavioural roots in higher animals and ancestral great apes.

...
Wikipedia