The common sayings related to food are generally colloquialisms.It' s useful to know them in order to improve your comprehesion of spoken Italian,but better to use the formal expressions that I write when I explain them.

PARLARE DELLA RAVA E DELLA FAVA means to speak about useless things ( more formal PARLARE A VANVERA)

CAPIRE TOMA PER ROMA or PRENDERE FISCHI PER FIASCHI or PRENDERE LUCCIOLE PER LANTERNE are idiomatic expressions with the same meaning: to misunderstand something completely.In Italian you can say AVER CAPITO MALE O FRAINTEDERE.

are there similar sayings in your language?