I answer that, Two things may be considered touching the matter of this sacrament namely, what is necessary, and what is suitable. It is necessary that the bread be wheaten, without which the sacrament is not valid, as stated above (A[3]). It is not, however, necessary for the sacrament that the bread be unleavened or leavened, since it can be celebrated in either.
But it is suitable that every priest observe the rite of his Church in the celebration of the sacrament. Now in this matter there are various customs of the Churches: for, Gregory says: "The Roman Church offers unleavened bread, because our Lord took flesh without union of sexes: but the Greek Churches offer leavened bread, because the Word of the Father was clothed with flesh; as leaven is mixed with the flour." Hence, as a priest sins by celebrating with fermented bread in the Latin Church, so a Greek priest celebrating with unfermented bread in a church of the Greeks would also sin, as perverting the rite of his Church. Nevertheless the custom of celebrating with unleavened bread is more reasonable. First, on account of Christ's institution: for He instituted this sacrament "on the first day of the Azymes" ( Mat. 26:17 ; Mk. 14:12 ; Lk. 22:7 ), on which day there ought to be nothing fermented in the houses of the Jews, as is stated in Exod. 12:15 , 19 Secondly, because bread is properly the sacrament of Christ's body, which was conceived without corruption, rather than of His Godhead, as will be seen later (Q[76], A[1], ad 1). Thirdly, because this is more in keeping with the sincerity of the faithful, which is required in the use of this sacrament, according to 1 Cor. 5:7 : "Christ our Pasch is sacrificed: therefore let us feast . . . with the unleavened bread of sincerity and truth."
However, this custom of the Greeks is not unreasonable both on account of its signification, to which Gregory refers, and in detestation of the heresy of the Nazarenes, who mixed up legal observances with the Gospel.
Reply to Objection 1: As we read in Ex. 12 , the paschal solemnity began on the evening of the fourteenth day of the moon. So, then, after immolating the Paschal Lamb, Christ instituted this sacrament: hence this day is said by John to precede the day of the Pasch, while the other three Evangelists call it "the first day of the Azymes," when fermented bread was not found in the houses of the Jews, as stated above. Fuller mention was made of this in the treatise on our Lord's Passion (Q[46], A[9], ad 1).
Reply to Objection 2: Those who celebrate the sacrament with unleavened bread do not intend to follow the ceremonial of the Law, but to conform to Christ's institution; so they are not Judaizing; otherwise those celebrating in fermented bread would be Judaizing, because the Jews offered up fermented bread for the first-fruits.
Reply to Objection 3: Leaven denotes charity on account of one single effect, because it makes the bread more savory and larger; but it also signifies corruption from its very nature.
Reply to Objection 4: Since whatever is fermented partakes of corruption, this sacrament may not be made from corrupt bread, as stated above (A[3], ad 4); consequently, there is a wider difference between unleavened and leavened bread than between warm and cold baptismal water: because there might be such corruption of fermented bread that it could not be validly used for the sacrament.
Whether wine of the grape is the proper matter of this sacrament?
Objection 1: It seems that wine of the grape is not the proper matter of this sacrament. Because, as water is the matter of Baptism, so is wine the matter of this sacrament. But Baptism can be conferred with any kind of water. Therefore this sacrament can be celebrated in any kind of wine, such as of pomegranates, or of mulberries; since vines do not grow in some countries.
Objection 2: Further, vinegar is a kind of wine drawn from the grape, as Isidore says (Etym. xx). But this sacrament cannot be celebrated with vinegar. Therefore, it seems that wine from the grape is not the proper matter of this sacrament.
Objection 3: Further, just as the clarified wine is drawn from grapes, so also are the juice of unripe grapes and must. But it does not appear that this sacrament may be made from such, according to what we read in the Sixth Council (Trull., Can. 28): "We have learned that in some churches the priests add grapes to the sacrifice of the oblation; and so they dispense both together to the people. Consequently we give order that no priest shall do this in future." And Pope Julius I rebukes some priests "who offer wine pressed from the grape in the sacrament of the Lord's chalice." Consequently, it seems that wine from the grape is not the proper matter of this sacrament.
On the contrary, As our Lord compared Himself to the grain of wheat, so also He compared Himself to the vine, saying ( Jn. 15:1 ): "I am the true vine." But only bread from wheat is the matter of this sacrament, as stated above (A[3]). Therefore, only wine from the grape is the proper matter of this sacrament.
I answer that, This sacrament can only be performed with wine from the grape. First of all on account of Christ's institution, since He instituted this sacrament in wine from the grape, as is evident from His own words, in instituting this sacrament ( Mat. 26:29 ): "I will not drink from henceforth of this fruit of the vine." Secondly, because, as stated above (A[3]), that is adopted as the matter of the sacraments which is properly and universally considered as such. Now that is properly called wine, which is drawn from the grape, whereas other liquors are called wine from resemblance to the wine of the grape. Thirdly, because the wine from the grape is more in keeping with the effect of this sacrament, which is spiritual; because it is written ( Ps. 103:15 ): "That wine may cheer the heart of man."
Reply to Objection 1: Such liquors are called wine, not properly but only from their resemblance thereto. But genuine wine can be conveyed to such countries wherein the grape-vine does not flourish, in a quantity sufficient for this sacrament.
Reply to Objection 2: Wine becomes vinegar by corruption; hence there is no returning from vinegar to wine, as is said in Metaph. viii. And consequently, just as this sacrament may not be made from bread which is utterly corrupt, so neither can it be made from vinegar. It can, however, be made from wine which is turning sour, just as from bread turning corrupt, although he who does so sins, as stated above (A[3]).
Reply to Objection 3: The juice of unripe grapes is at the stage of incomplete generation, and therefore it has not yet the species of wine: on which account it may not be used for this sacrament. Must, however, has already the species of wine, for its sweetness [*"Aut dulcis musti Vulcano decoquit humorem"; Virgil, Georg. i, 295] indicates fermentation which is "the result of its natural heat" (Meteor. iv); consequently this sacrament can be made from must. Nevertheless entire grapes ought not to be mixed with this sacrament, because then there would be something else besides wine. It is furthermore forbidden to offer must in the chalice, as soon as it has been squeezed from the grape, since this is unbecoming owing to the impurity of the must. But in case of necessity it may be done: for it is said by the same Pope Julius, in the passage quoted in the argument: "If necessary, let the grape be pressed into the chalice."
Whether water should be mixed with the wine?
Objection 1: It seems that water ought not to be mixed with the wine, since Christ's sacrifice was foreshadowed by that of Melchisedech, who ( Gn. 14:18 ) is related to have offered up bread and wine only. Consequently it seems that water should not be added in this sacrament.
Objection 2: Further, the various sacraments have their respective matters. But water is the matter of Baptism. Therefore it should not be employed as the matter of this sacrament.
Objection 3: Further, bread and wine are the matter of this sacrament. But nothing is added to the bread. Therefore neither should anything be added to the wine.
On the contrary, Pope Alexander I writes ( Ep. 1 ad omnes orth.): "In the sacramental oblations which in mass are offered to the Lord, only bread and wine mixed with water are to be offered in sacrifice."
I answer that, Water ought to be mingled with the wine which is offered in this sacrament. First of all on account of its institution: for it is believed with probability that our Lord instituted this sacrament in wine tempered with water according to the custom of that country: hence it is written ( Prov. 9:5 ): "Drink the wine which I have mixed for you." Secondly, because it harmonizes with the representation of our Lord's Passion: hence Pope Alexander I says ( Ep. 1 ad omnes orth.): "In the Lord's chalice neither wine only nor water only ought to be offered, but both mixed because we read that both flowed from His side in the Passion." Thirdly, because this is adapted for signifying the effect of this sacrament, since as Pope Julius says (Concil. Bracarens iii, Can. 1): "We see that the people are signified by the water, but Christ's blood by the wine. Therefore when water is mixed with the wine in the chalice, the people is made one with Christ." Fourthly, because this is appropriate to the fourth effect of this sacrament, which is the entering into everlasting life: hence Ambrose says (De Sacram. v): "The water flows into the chalice, and springs forth unto everlasting life."
Reply to Objection 1: As Ambrose says (De Sacram. v), just as Christ's sacrifice is denoted by the offering of Melchisedech, so likewise it is signified by the water which flowed from the rock in the desert, according to 1 Cor. 10:4 : "But they drank of the spiritual rock which came after them."
Reply to Objection 2: In Baptism water is used for the purpose of ablution: but in this sacrament it is used by way of refreshment, according to Ps. 22:3 : "He hath brought me up on the water of refreshment."
Reply to Objection 3: Bread is made of water and flour; and therefore, since water is mixed with the wine, neither is without water.