egg in your beer
A bonus, something for nothing, as in What do you want—egg in your beer? This expression dates from about 1940 and became widespread during World War II. The origin is unknown, since adding egg to beer does not improve the taste.
Why Is The Word “Root” In “Root Beer”?Is root beer the world's most oddly named carbonated beverage ... we don't know, that award might go to 7-up, but we're going to explore the naming of this soft drink regardless. What, after all, is the root in root beer?
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.