For reasons unknown to me, many parishes use sherry. This is a fairly arcane topic, not of great interest to most of us.
1 Now, because, as was said above, this sacrament is accomplished with bread and wine, those conditions necessarily must be observed to accomplish this sacrament therefrom which belong to the essentials of bread and wine.
But one calls wine only that liquid which is pressed from grapes, and one calls bread, properly speaking, only that which is made from grain wheat. But other so-called breads, for lack of wheat bread and to supplement it, have come into use; in a like way, other liquids have come into use with wine. Hence, neither from some other bread nor from some other wine could this sacrament be accomplished, especially not if the mixture of foreign matter with bread or wine be so considerable that the species is lost.
2 However, if things happen to this sort of bread and wine which do not touch the essentials of bread and wine, manifestly one may pass these things over, and truly accomplish the sacrament. Wherefore, since to be leavened or unleavened is not essential to bread—rather, whichever of the two is the case, the species of bread is preserved—the sacrament can be accomplished from either of the two breads.
This is the reason why different churches have different customs in this matter, but each of the two can be in harmony with the significance of the sacrament. For, as Gregory puts it in his Register: “The Roman Church offers unleavened bread because our Lord took on flesh without any mixture. But the rest of the Churches offer leavened bread, since the Word of God was clothed with flesh, and is true God and true man, just as the leaven is mixed with the paste.”
3 Nonetheless, there is greater harmony with the purity of the mystical body, that is, the Church, of which there is also a figure in this sacrament, in the use of unleavened bread; as the Apostle has it: “Christ our pasch is sacrificed. Therefore let us feast… with the unleavened bread of sincerity and truth” (1 Cor. 5:7-8).
Notes Hence the bland taste.
4 Thus does one exclude the error of certain Greeks, who deny that this sacrament can be celebrated with unleavened bread. And this is even clearly destroyed by the Gospel’s authority, for we read in Matthew (26:17), in Mark (14:12), and in Luke (22:7) that on the first day of the unleavened bread our Lord ate the pasch with His disciples, and at that time instituted this sacrament. Now, since it was not permitted by the Law that from the first day of the unleavened bread anything leavened be found in the homes of the Jews (which is clear from Exodus 12:15), and since our Lord as long as He was in the world kept the Law, clearly He converted unleavened bread into His body and gave it to His disciples to receive. It is stupid, then, to attack in the use of the Latin Churches what our Lord observed in the very institution of this sacrament.
5 For all that, one must acknowledge that some say He anticipated the day of the unleavened bread with His passion so near, and, then, used leavened bread. Indeed, to support this they rely on two things. First, there is what John (13:1) says, that “before the festival day of the pasch” our Lord celebrated the feast with His disciples, and at this feast consecrated His body, as the Apostle tells us (1 Cor. 11:23).
Hence, it seems that Christ celebrated the feast before the day of the unleavened bread, and so, in the consecration of His body, used leavened bread. Also, they want to confirm this by what is found in John (18:28): that on the Friday on which Christ was crucified the Jews did not enter the pretorium of Pilate, “that they might not be defiled but might eat the pasch.” But the pasch is called the unleavened bread. Therefore, they conclude that the feast had been celebrated before the unleavened bread.
6 Now, to this one answers that, as the Lord commands in Exodus 12, “the feast of the unleavened bread was celebrated for seven days, and of these the first day was especially holy and solemn among the others, and it was the fifteenth day of the month.” But, since among the Jews the solemnities used to begin on the preceding evening, they therefore on the evening of the fourteenth day began to eat the unleavened bread and they ate it for seven days following.
And, therefore, we read in the same chapter (Ex. 12:18-19): “The first month, the fourteenth day of the month in the evening you shall eat unleavened bread until the one and twenties day of the month in the evening. Seven days there shall not be found any leaven in your houses.” And on the same fourteenth day in the evening they used to sacrifice the paschal lamb.
Therefore, the first day of the unleavened bread is the way the three Evangelists—Matthew, Mark, and Luke—name the fourteenth day of the month, because in the evening they used to eat the unleavened bread, and then “they sacrificed the pasch,” that is, “the paschal lamb”; and this, according to John, was before the festival day of the pasch,” that is, the day before the fifteenth day of the month which was the most solemn day of all, and on this day the Jews wanted to eat the pasch, that is, “the unleavened paschal bread,” not, of course, the paschal lamb. And thus, since no discord exists among the Evangelists, it is plain that Christ consecrated His body from unleavened bread at the feast. Hence it becomes clear that the Church of the Latins reasonably uses unleavened bread in this sacrament.