Sensitized by the recent media hype about so-called heretical gospels, such as the Gospel of Thomas or the Gospel of Judas, and the editorial success of controversial projects, like The Gnostic Bible (Boston, Mass.: Shambhala, 2003), the general public associates to a large extent the scandal of ancient heretics with what those putative dissidents and schismatics allegedly taught. But doctrine was not everything that made you a heretic in the ancient world. For the late antique heresiologists there was more to heretics than some controversial or deviant teachings. Christian heresiology, the notorious “science of heresies”, was not for nothing perhaps the most creative enterprise in concocting religious identities in antiquity. It displayed a sophistication in scandalogy, rhetoric, and the intricacies of various ancient fields of knowledge that astonishes modern readers time and again. The teachings of heretics—whether real, distorted, or simply invented—played without question a key role in the early compilations of heresy catalogues, a new form of religious knowledge that mimicked established genres of classification and systematization which were common among various ancient disciplines, such as natural history, philosophy, medicine, etc. With the fourth century, however, and the major transformations of late Roman society, we witness an intriguing new trend in Christian heresiology. In a number of heresy catalogues, polemical tracts, letters, and other writings of the Christian intelligentsia, the heretic is no longer exclusively defined by his doctrine but also by his diet: what went into the mouths of heretics became suddenly important, not only what came out of it. My paper will attempt to contextualize this intriguing concern of Christian heresiologists with the dietary regimen of heretics and propose a set of explanations for this gustatory curiosity in the late antique organization of the knowledge of the other. Toward that end I will revisit classical examples, such as the infamous discussion by Epiphanius of Salamis (d. 403 CE) of the Borborites, and I will add new, hereto undiscussed, material to the hardly palatable dossier of heretical diet in Christian antiquity.