Q: In selecting wine for Communion, is it necessary for the wine to be kosher?”
A: Christ has given us the Sacrament of the Altar in which we are assured that we are offered his true body and blood, along with the visible elements of bread and wine. Since it is bread and wine which the Lord used, one naturally will wish to be careful in selecting these elements for this sacramental use. Just as it is unessential to the Sacrament whether the bread be leavened or unleavened, wafers or baked loaves, so also it is unessential whether red wine or white wine be used, or whether the wine be 100% pure or mixed with water. The wine, however, is not to be of another fruit; it is to be grape wine, “the fruit of the vine.” On page 168 in his Pastorale, Dr. C. F. W. Walther explains that, both with regards to the bread and wine, the form of the elements is indifferent.
It is a good practice, though not mandatory, to select wine that is made for sacramental purposes (pure), and to stay with the reddish color, so that recipients at the altar will not be distracted in their thoughts as they commune.