Cut the bread into 1 to 1 1/2 inch cubes. You do not need to remove the crust. Arrange the bread cubes on a tray and let stand at room temperature until very dry. This may take a day or two in hot, dry weather or up to several days if the humidity is high. In damp weather you may need to finish the drying in a 200°F oven for about 1 hour. Let cool completely before grinding.

Working in batches, place the bread cubes in a food processor and whir until reduced to very fine crumbs. Transfer the crumbs to a large bowl.

When all the bread is ground, pass the crumbs through a medium-mesh sieve, using your hand to push them through. Reprocess and resieve the crumbs that do not pass through. Discard any crumbs that do not make it through the sieve a second time.

Freeze in 1- or 2- cup freezer bags for convenience.