As Catholics we believe that Jesus Christ is really present in the consecrated bread and wine at Mass.  “The Real Presence is the result of the effective power of the Word of God.  In the action of the Mass, the substance of bread and wine is changed into the Body and Blood of Christ, while the accidents of bread and wine (shape, taste, colour, weight) remain.  This is called transubstantiation. Essential Catholic doctrine is that a real but mysterious change, not visible to the senses, is effected by the Holy Spirit at the consecration.  The bread and wine become the Body and Blood of Christ.”  Faith Alive