The hedonic impact of taste is reflected in affective facial reactions made by human infants, other primates, and even rats. Originally studied in human infants, affective reactions to taste have also been used by affective neuroscience to identify hedonic brain systems in studies of animals (via application of neural stimulation, pharmacological activation, and neural lesion manipulations). The chief limitation of measuring affective reactions is that it is difficult for experimenters to know how to interpret them, and therefore how to interpret changes produced by brain manipulations. This paper notes guidelines to interpretation. It examines the phylogenetic continuity between humans, other primates, and rats in terms of the microstructure of taste-elicited affective reactions. It reviews evidence that affective taste reactivity patterns truly reflect a 'core hedonic process' of palatability or affect, rather than being an ingestion measure, consummatory behavior measure, or a sensory reflex measure. It reviews affective neuroscience studies of taste reactivity that have identified true hedonic brain substrates, and discriminated them from false hedonic brain substrates. It considers the neural bases of incentive 'wanting' versus 'liking'. Finally, it notes the difference between human subjective affective ratings of pleasure and 'core hedonic processes' reflected by behavioral affective reactions.