The Holy Eucharist consisting of bread and wine before consecration must follow strict guidelines in order for transubstantiation to take place.  The following elements must be present, per the Congregation for Divine Worship:

1.  “The bread used in the celebration of the Most Holy Eucharistic Sacrifice must be unleavened, purely of wheat, and recently made so that there is no danger of decomposition. It follows therefore that bread made from another substance, even if it is grain, or if it is mixed with another substance different from wheat to such an extent that it would not commonly be considered wheat bread, does not constitute valid matter for confecting the Sacrifice and the Eucharistic Sacrament. It is a grave abuse to introduce other substances,such as fruit or sugar or honey, into the bread for confecting the Eucharist."

2.  “The wine that is used in the most sacred celebration of the Eucharistic Sacrifice must be natural, from the fruit of the grape, pure and incorrupt, not mixed with other substances. […] Great care should be taken so that the wine intended for the celebration of the Eucharist is well conserved and has not soured. It is altogether forbidden to use wine of doubtful authenticity or provenance, for the Church requires certainty regarding the conditions necessary for the validity of the sacraments. Nor are other drinks of any kind to be admitted for any reason, as they do not constitute valid matter”

You can read the official document below, as published by Robert Cardinal Sarah, prefect of the CDW.