The phrase "crusty piece" refers to something that is old, dirty, or worn out. It usually describes an object that is not in a good condition. Full definition
With the bacon on top and a nice crusty piece of bread you have a great quick meal. (peasandcrayons.com)
Such a perfect soup to make ahead for busy nights to serve alongside a sandwich or crusty piece of whole grain bread. (aggieskitchen.com)
The ratatouille tastes delicious served over brown rice, couscous or quinoa, and although I have yet to try it, I'm betting it would be awesome scooped onto a nice crusty piece of French bread, too. (heatovento350.com)