Proskomide

The Liturgy of Preparation, also Prothesis (Greek: Πρόθεσις "a setting forth") or Proskomedia (Προσκομιδή Proskomidē "an offering, an oblation"), is the name given in the Eastern Orthodox Church to the act of preparing the bread and wine for the Eucharist. The Liturgy of Preparation is done quietly before the public part of the Divine Liturgy begins, and symbolizes the "hidden years" of Christ's earthly life.

Only very specific elements may be offered at the Divine Liturgy:

The bread used for the Liturgy is referred to as prosphora. A prosphoron is a round loaf of leavened bread baked in two layers to represent the two natures of Christ. It has a square seal on the top side which has inscribed on it a cross and the Greek letters IC (an abbreviation in Greek for "Jesus") XC ("Christ") and NIKA ("Conquers"). The portion of the loaf that is cut out along this seal is the Lamb (Host), from which all are communicated, and therefore must be proportionately large for the number of communicants.

Prosphora must be made using only the finest wheat flour, water, salt, and yeast. It should be freshly baked and without blemish.

The Greeks use one large loaf for the Liturgy of Preparation, with a large round seal on it inscribed not only with the square seal mentioned above (from which the Lamb is taken), but also markings indicating where the portions for the Theotokos, the Ranks, the Living and Dead are removed (see Proskomedie, below).

Those churches which follow Slavic usage use five small loaves, recalling the five loaves from which Christ fed the multitude (John 6:5-14). Normally all are stamped with a small square seal, though special seals for the Theotokos are sometimes used.

In all traditions, only the Lamb is actually consecrated, other portions which are removed from the prosphora are memorials, but are never to be used for Communion.

The Wine used must be red grape wine, and it must be fermented. Orthodox tend to favor altar wine that is somewhat sweet, though this is not a requirement.

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Wikipedia