A committee had been appointed to investigate after the host turned water red at Saint Francis Xavier Catholic Church in Kearns on November 8.
Committee chairman Monsignor Francis Mannion said the church sets a high bar for proving a miracle and rules one out if an event has a conclusive natural explanation.
Officials said a scientist found a 'conclusive natural explanation' for the wafer that turned water in an ablution bowl a dark red colour.
The scientist said it had gone off and was mouldy after being left out for some time.
The diocese said it was important to find false claims of miracles so as not to undermine the Church's credibility.