"Holy Leaven, also known as Malka (Classical Syriac: ܡܲܠܟܵܐ, pronounced [' mal ka:]),[1][note 1] is a powder added to the sacramental bread used in the Eucharist of both the Ancient Church of the East and the Assyrian Church of the East and historically in the Church of the East. Both churches hold the Holy Leaven to be one of their seven sacraments. There are two rituals associated with the Holy Leaven: its addition to sacramental bread before it is baked, and the annual renewal of the Holy Leaven itself. The origin of the Holy Leaven supposedly goes back to the Last Supper. According to various traditions, John the Apostle kept a piece of bread given to him by Jesus and later mixed it with Jesus' blood after his death. This substance was divided between the apostles to be used in preparing sacramental bread ever since and successfully brought to the Christians of the East. The earliest historical mention of the Holy Leaven is from c. 900, and tradition that connects it with the Last Supper is fairly new, dating from the 13th and 14th centuries. It is likely that the Holy Leaven is a symbol instituted to unify congregations by the Patriarchate of Seleucia-Ctesiphon during vast missionary expansion of the Church of the East." - Wiki