It seems that despite all our efforts to avoid waste, we always have a heel or three of stale bread lying around. So we let it get really dry, grind it up in the food processor, and add it to our ongoing jar in the fridge. Wheat bread, white bread, sourdough, semolina—all work fine.
Store-bought breadcrumbs are not only overpriced but full of harsh-tasting chemicals. (A can of “Italian” crumbs at our supermarket has an ingredient list that’s three inches long.) We don’t know why the manufacturers add so many preservatives, as in our experience, refrigerated crumbs don’t go bad.
Some cooks say never to use stale bread, lest you wind up with offensively stale crumbs. We’ve never had a problem, though, maybe because our crumbs are either mixed with good olive oil and herbs as a topping or incorporated into a dish with other ingredients. If you have an extremely delicate palate, go ahead and freeze them, but the same principle holds: if you diligently use up your odds and ends of bread, you’ll never have to buy nasty store crumbs again.