Article: The Catholic Church uses wine in the celebration of the Eucharist because it is part of the tradition passed down through the ages starting with Jesus Christ at the Last Supper, where Catholics believe the consecrated bread and wine literally become the body and blood of Jesus Christ, a dogma known as transubstantiation. Wine is used (not grape juice) both due to its strong Scriptural roots, and also to follow the tradition set by the early Christian Church. The Code of Canon Law of the Catholic Church (1983), Canon 924 says that the wine used must be natural, made from grapes of the vine, and not corrupt. In some circumstances, a priest may obtain special permission to use grape juice for the consecration, however this is extremely rare and typically requires sufficient impetus to warrant such a dispensation, such as personal health of the priest.

Now answer this question: Where in the Code of Canon Law does it say that wine must be natural and not corrupt?
Canon 924