A fruit fly has landed in your wine – is it OK to drink?
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In the 16th Century, while the Protestant Reformation raged in Europe, the Council of Trent was held to address this, and the Mass was being reformed into what we know today as the Tridentine Mass. Great changes were afoot, and saints were being made every day.
Pope St. Pius V issued a document called De defectibus, and this document was attached to every copy of the Roman Missal that was published for 500 years.
De defectibus is a marvelous checklist for priests, of what to do when things don't quite go your way as you're celebrating a Mass. This could consist of missing materials or mistakes in prayers or the intrusion of the natural world.
http://www.dailycatholic.org/defectib.htm
As you can see, items #35-37 are very specific about what to do when a fly, spider, or something poisonous comes in contact with the wine, bread, or consecrated elements.
It is important to note that these items appear to pertain only to elements which the priest himself would be consuming. In general, the communicants at a Tridentine Mass never, ever drank from the chalice. Any ciborium holding hosts for the faithful would naturally have a cover, and would not generally need to be uncovered for very long, so the danger of something falling into this receptacle is remote.
Priests have had a little fun with this since then: https://wdtprs.com/2008/02/scholion-consecration-of-a-paten-...
The possibilities and solutions get amusing once you know the burining/washing/sacrarium principle. At a very clerical supper one night we mused about the possibility of a mouse dashing across the altar after the consecration and making off with a Host. Our solution was to bless a cat, put a white stole on it, send it after the rat, and when it came back, burn the cat and put the ashes, yes, down the sacrarium.