I guess most here know this one. Does its meaning stem from some American colonial times? It must be more rare than I thought as I did find any information.
As far as I know it essentially means to cull, or select the good/useful parts from the whole.
In German there's the self-explanatory 'die Spreu vom Weizen trennen' (to separate the wheat from the chaff), but the idiom isn't as clear cut in English. Are we separating the useful/good English from the unwanted Dutch here?.
I'd be interested to learn other foreign equivalents too :-)