THE PROPER CELEBRATION OF MASS
1. The Matter of the Most Holy Eucharist
[48.] The bread used in the celebration of the Most Holy Eucharistic Sacrifice must be unleavened, purely of wheat, and recently made so that there is no danger of decomposition. It follows therefore that bread made from another substance, even if it is grain, or if it is mixed with another substance different from wheat to such an extent that it would not commonly be considered wheat bread, does not constitute valid matter for confecting the Sacrifice and the Eucharistic Sacrament. It is a grave abuse to introduce other substances, such as fruit or sugar or honey, into the bread for confecting the Eucharist. Hosts should obviously be made by those who are not only distinguished by their integrity, but also skilled in making them and furnished with suitable tools.
[49.] By reason of the sign, it is appropriate that at least some parts of the Eucharistic Bread coming from the fraction should be distributed to at least some of the faithful in Communion. “Small hosts are, however, in no way ruled out when the number of those receiving Holy Communion or other pastoral needs require it”, and indeed small hosts requiring no further fraction ought customarily to be used for the most part.
[50.] The wine that is used in the most sacred celebration of the Eucharistic Sacrifice must be natural, from the fruit of the grape, pure and incorrupt, not mixed with other substances. During the celebration itself, a small quantity of water is to be mixed with it. Great care should be taken so that the wine intended for the celebration of the Eucharist is well conserved and has not soured. It is altogether forbidden to use wine of doubtful authenticity or provenance, for the Church requires certainty regarding the conditions necessary for the validity of the sacraments. Nor are other drinks of any kind to be admitted for any reason, as they do not constitute valid matter.