A reader inquired about this expression and I’m once again relying on the Phrase Finder for the origin. It means “items of quality offered to those who aren’t cultured enough to appreciate them.” The expression may have originated in France in the early 1400s.   In appeared in Matthew 7:6 of Tyndale’s Bible, in 1526, “Nether caste ye youre pearles before swyne.” “The biblical text is generally interpreted to be a warning by Jesus to his followers that they should not offer biblical doctrine to those who were unable to value and appreciate it.”