It is customary to add a little water to the wine in preparing the altar for the eucharistic prayer. This custom is known as the "mixed chalice." Wine of any color may be used at the eucharist. There is to be only one chalice on the altar during the prayer of consecration. Additional chalices may be filled from a flagon containing consecrated wine after the eucharistic prayer is completed. If there is insufficient wine to distribute to the people, additional wine may be consecrated by the celebrant. Any consecrated wine that is not administered at communion may be consumed by the ministers, reserved, or disposed of in a reverent manner. Some Protestant churches substitute grape juice for wine and substitute individual small cups for the common chalice or cup at their celebrations of communion. See Concomitance; see Elements, Eucharistic; see Matter (Sacramental); see Mixed Chalice; see Real Presence.