Hello dear brothers Cody and Justin. Greetings in Christ to both of you dear ones.
I am no expert in New Testament Greek, but my understanding exactly matches what dear brother Justin wrote. In Ancient times the juice was squeezed from grapes in a winepress, and if this juice was consumed before it began to ferment, then it would have been what we today call "grape juice".
My understanding is that the Greek word "wine" covers the full range of "grape juice", from its initial fresh, unfermented, state all the way to fully fermented. As brother Justin pointed out, the three Synoptic Gospels all utilize the phrase "fruit of the vine" to convey the words spoken by Jesus to His disciples when they partook of the first Lord's Supper the night He was betrayed (Matthew 26:29, Mark 14:25, Luke 22:18).
Since fresh grape juice is the "fruit of the vine" as much as grape juice that has fermented, it certainly appears that fresh grape juice is totally acceptable.
Dear brother Cody - there is actually some help we can receive from the Early Christian Writers regarding this matter.
Even if their "grape juice" was somewhat fermented (and was what we would today call "wine"), there are multiple places in their writings where they clearly state that they mixed the "wine" with water during their times of partaking of the Eucharist/Communion. Below is a very clear example of that from Justin Martyr's First Apology, chapter 65 (notice that in this passage there are two references to "wine mixed with water"):
Having ended the prayers, we salute one another with a kiss. There is then brought to the president of the brethren bread and a cup of wine mixed with water; and he taking them, gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Ghost, and offers thanks at considerable length for our being counted worthy to receive these things at His hands. And when he has concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen answers in the Hebrew language to γενοιτο . And when the president has given thanks, and all the people have expressed their assent, those who are called by us deacons give to each of those present to partake of the bread and wine mixed with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion.
(Link to the primary source: Resource on logoslibrary.org — http://www.logoslibrary.org/justin/apology1/65.html )
I know there are other references to the Communion "wine" being mixed with water in the Early Christian Writings. Based upon the Bible's very clear warnings against drunkenness, and the fact that strong wine was used in many unholy pagan practices, I do not believe that the Early Christians used undiluted strong wine.
Cyprian, at the very least, also mentioned that their "wine" was mixed with water. As always, I welcome further discussion and fellowship on this matter, dear saints of God. In addition, there is a course entitled "Communion" on this web site in the class entitled "Church Life A.D. 150". This topic is mentioned in the audio recording for that class.
May our dear Lord bless richly bless you both as you seek first His kingdom and His righteousness.
Grace and peace and love be with you in abundance.