Just found the time to do a bit more research on this and I believe I'm near enough to the answer to close off the thread, unless there are some Latin scholars out there who want to post in with late corrections/comments.

I think this is the Latin text of the grace in question:

Domini qui aperis manum tuum et omnia impletur
bonitate benedicere dignare cibum istum
et nos ex eo iustate inde corporis et animi
accipiamus sanitatum
per Jesum Christum Dominum Nostrum

and the (rough) translation:

Our Lord who open your hands and satisfies all with goodness deign to bless your food and thereupon from it we will justly receive health of body and mind. Through Jesus Christ Our Lord.

Thanks to useful Latin translation and grammar sites:
http://www.nd.edu/~archives/latgramm.htm
and
http://lysy2.archives.nd.edu/cgi-bin/words.exe

And a final contribution from our spell-checker Aenigma in the form of the following correction to the Latin:

Dominic quibble aperture manure twain et omnibus implicant Bonn Benedict dignified cicada Istvan et nose ex Eocene Ivan indebted corps et animism acclaim sanity
per Jesus Christy Don not

...which appears to be a story about a guy called Dominic quibbling with two ass-holes that he met on a bus. One of the implicated guys was a German monk with a noble cricket called Istvan. The other one, nosy Ivan the Fossil, is beholden to the army and the spirit world, and swears, by Jesus and Professor Christy, that he is sane. {Not!)

Now that might have caused some mirth before dinner!