Lighty toast the ends of bread as you finish up a loaf of bread. Be careful not to over-toast. You just want to dry out the moisture.
Let toast sit in toaster after it toasts for a few hours to be sure it's extra dry, then transfer the toasted bread ends back to the bread bag for storage. Store in pantry. (No need to refrigerate)
When you have about 8 pieces of bread saved up (I use a mix of whatever breads I have one hand), crumble the toasted pieces into chunks small enough to fit into your mason jar or blender or food processor. Use the pulse feature to break up the toast into crumbs.
Use your regular Mason jar lid or get yourself the Ball Jar shaker cap to break up clumps when ready to use your bread crumbs.