Grist for or to the mill

The complete saying is that something or other is grist for or to the mill. For example, if a person as a guest brings something for a host's barbecue, the host might say, 'Thank you. That is all grist for the mill', meaning that it is of added value or benefit. This idiomatic metaphor dates from the 1500s. 'Grist' is an Old English word that means to grind, and dates from before 1150. It also means the batch or amount of grain that is to be ground at the mill. Grain farmers rarely owned their own mill, so they would take their harvest or their grist to the local mill, where the miller would grind it for them. The miller would either charge a fee or take a portion of what was ground for his or her services.