Unlike previous approaches, which were limited to predicting one to two taste classes, FART is capable of classifying molecules across four of the basic human taste categories: sweet, bitter, umami and sour. The category of "salty" was excluded as it is predominately elicited by salts containing sodium and chloride ions. Unlike other taste modalities, the perception of saltiness is largely determined by physical properties such as ion size and solubility rather than molecular structure . Instead, we opted to include a category of "undefined" tastants, which includes tasteless as well as molecules with ambiguous taste profiles.