Canon Law § 924 states:
§1. The most holy Sacrifice of the Eucharistic must be offered in bread, and in wine in which a small quantity water is to be added.
§2. The bread must be wheaten only, and recently made, so that there is no danger of corruption.
§3. The wine must be natural, made from grapes of the vine and not corrupt.
Commentary from “The Code of Canon Law Annotated, Midwest Theological Forum, Woodbridge, 2004, pp. 714-715:
“By divine institution bread and wine are the indispensable material for the constitution of the sacrament. The “bread” must, of necessity, be of wheat. Taking into account the danger of corruption, the practice of obtaining a sufficient amount of wafers to last two to three months is expressly condemned (Reply of the S, Congr. For the discipline of the Sacraments, 07-12-1918, AAS 11, [1919] 8; CLD 1 [1917-1933] 352-353; for this reason, common doctrine has maintained the term of one month as the maximum limit between the making of the host and its consumption. In its turn, c. 934, § 2, requires as a condition for reserving the Eucharist that Mass be celebrated twice a month in the place authorized for this purpose. It seems that two weeks is the maximum appropriate delay according to the mind of the legislator. In any case, the climate and the conditions of preservation must be carefully considered, given the fact that there is greater danger of corruption, or at least of the softening of the wafers, whereever there is a greater degree of humidity (cf. Institio generalis Missalis romani 323; cf. also S, Congr. For Divine Worship, Instr, Actio pastoralis 10, 15-05-1969, AAS 61 [1969] 810; CLD 7 [1968-1972] 641; and Instr. Liturgicae instaurationes 5, 05-09-1970, AAS 62 [1970] 692-704; CLD 7 [1968-1972] 46-47.
“Following the tradition of the Latin Church, the bread must be unleavened (Institio generalis Missalis romani, edition typica tertia [2000] 320, c. 926. Regarding the external form of the host, “semper forma tradita conficiendus est” (Instr. Liturgicae instaurationes 5, which refers expressly to the Institio generalis Missalis romani 320, whether the wafers are small for the distribution of communion to the faithful or larger ones that must be broken up. Where there is a large number of faithful, small wafers “are in no way ruled out” (Institio generalis Missalis romani [2000] 321). In any case, in view of the reverence due to the sacrament, great care must be taken in making the bread, so that it may be broken up decorously and its reception not offend the sensitivity of the faithful (Instr. Liturgicae instaurationes 5).
“In the case of the wine, the same provisions must be observed regarding its purity (pure and natural from the vine) and the state of preservation. Although it does noy affect the validity of the sacrament, a precept of theChurch prescribes the addition of several drops of water to the wine. The canon thus echoes the provision of the Council of Trent (Sess, XXII, de sacrificio Missaem chs. 7 and 9, D 1747 and 1750.
Regarding the permission to use eucharistic bread containing a little dluten as well as mustum, cf, Letter Hoc Dicasterium of the Congr. Of the Doctrine of the Faith of 19-06-1995 (Notitiae 31 [1995} 608-610; Or 25 [1995-1996] 191-192, plus marginal comments on pp. 191-193.”
As you can see from the above, “the wine must be natural, made from grapes of the vine.” There can be an exception to this rule to accommodate a priest who suffers from alcoholism
The question of the validity of the use of “mustum,” or grape juice, for priests suffering from alcoholism or for some other medical reason was finally resolved by the Congregation for the Doctrine of the Faith in 1994 in a letter signed by then Cardinal Joseph Ratzinger. Among other things this letter stated:
“A. The preferred solution continues to be communion ‘per intinctionem,’ or in concelebration under the species of bread alone.
“B. Nevertheless, the permission to use ‘mustum’ can be granted by ordinaries to priests affected by alcoholism or other conditions which prevent the ingestion of even the smallest quantity of alcohol, after presentation of a medical certificate.
“C. By ‘mustum’ is understood fresh juice from grapes or juice preserved by suspending its fermentation (by means of freezing or other methods which do not alter its nature).
“D. In general, those who have received permission to use ‘mustum’ are prohibited from presiding at concelebrated Masses. There may be some exceptions however: in the case of a bishop or superior general; or, with prior approval of the ordinary, at the celebration of the anniversary of priestly ordination or other similar occasions. In these cases, the one who presides is to communicate under both the species of bread and that of ‘mustum,’ while for the other concelebrants a chalice shall be provided in which normal wine is to be consecrated.”
The document required furthermore that the ordinary must ascertain that the matter used conforms to the above requirements; that he grant permission only for as long as the situation continues which motivated the request; and that scandal be avoided.
The precise question in hand is addressed in points A and D. The priest in question should therefore not normally preside at a concelebration except for very special occasions. When such a situation arises, two chalices must be provided: one with mustum and another with ordinary wine.
Likewise, if the priest presides alone at a religious community Mass where Communion under both kinds is habitual for religious seminarians, then a second chalice with ordinary wine should also be provided. A deacon or at least an instituted acolyte should also be present to assure that the Precious Blood is fully consumed after Communion.
The bottom line is that if a priest used anything except wine, with the above exception for an alcoholic priest, the priest would not be confecting a valid Eucharist and therefore the Mass would be invalid.