Instructions

1. Stale bread works better here than fresh. A day-old loaf has already given up some of its water, so it goes brittle sooner and the crumb breaks cleanly instead of squashing under the knife.
2. Use whatever bread you have, but keep one kind to a tray. A dense sourdough and a soft sandwich loaf will not finish together, and the batch is only done when the slowest slice is.
3. Lay the slices flat with a finger of space around each one. Bread is thick enough that the air has to reach both faces, and slices that touch stay pale and soft where they meet.
4. Dry at 52 °C for 4 hours. Snap a slice from the middle of a tray once the time is up: it should break with a sharp crack and no give at the centre, and the torn edge should look the same all the way through.
5. Any slice that bends rather than snaps goes back on. The centre is where the water hides, so test a thick slice rather than a corner one.
6. Bring the slices to room temperature on a rack before you crush them. Bread coming out of the machine feels crisper than it is, and warm crumbs packed into a jar will go soft overnight.
7. Break the slices by hand for coarse crumbs, or pulse them in a food processor for fine ones. Coarse suits a crust or a stuffing; fine is what you want for coating.
8. Keep the crumbs in a sealed jar in the cupboard and they hold for six months. If the loaf had seeds or oil in it, use them within a month instead — it is the oil that goes rancid, not the crumb.