the article "Opinion of the Department of Systematic Theology: The Fruit of the Vine in the Sacrament of the Altar" (Concordia Theological Quarterly, January - April 1981), in which they leave no doubt that there can be no substitute for wine in the Sacrament of the Altar.
The Scriptural texts leave no doubt that Christ was celebrating the Passover meal with His disciples. Among the foodstuffs on the table would have been unleavened bread and wine. As regards the latter, it was without question the fermented product of the grape vine, in view of the fact that this was the spring of the year, probably April. Moreover, wine was the customary drink of the Jews at solemn festival meals, the peri haggephen (liturgical Hebrew for "fruit of the vine"). There can be no doubt then, as Lenski points out, that this fruit of the vine" - with emphasis on the this - which the Passover cup contained "shuts out any and all other products of the vine save actual wine and thwarts all modern efforts that speak of unfermented grape juice, raisin tea, or diluted grape syrup" (Commentary on Matthew, p. 1028). The point is that "fruit of the vine" is a technical term which in the stated contexts can have no other meaning than wine. The church has never, from that day forward, felt at liberty to alter the solemn testament given by Christ in conjuction with the bread and the wine of the Sacrament (cf. Matt. 28:20; Gal. 3: 15). Whenever such altering or substitution was introduced, it was promptly repudiated, lest any doubt be cast upon the validity of the sacrament as Christ instituted it.
photo credit: Vainsang