We always provide unleavened bread at our annual Lord's Supper on Nisan 14, but leavened bread may also be provided then, too. Similarly, the significance of the wine is not its fermentation. The significance is that it is liquid, thus allowing it to represent Jesus' blood of the new covenant, and that we drink it, symbolizing our taking the new covenant into ourselves. Therefore we allow juice to be used for communion. We always have wine at our annual Lord's Supper, but we also offer grape juice in consideration for those who have reason to avoid wine.
Some people avoid wine because of allergies.
Others avoid it because their body reacts with alcohol in undesirable ways. Some Christians in less-developed nations simply find it difficult to find wine. That is why substitutes are permissible. The effectiveness of the ceremony does not depend on chemistry, but on our relationship with God. The Lord's Supper is for people who have faith in Jesus Christ as Lord and Savior, even if they have not been baptized yet.