know (one's) beans

(redirected from knows his beans)

know (one's) beans

To be knowledgeable about and/or very familiar with something. I had no idea you were such a good piano player—you really know your beans!
See also: bean, know
References in periodicals archive ?
But regardless of bias or technology, no roastmaster who really knows his beans thinks for one minute that every coffee has the same optimal roast point.