Instructions

1. Drain the olives and leave them in a sieve for half an hour, then pat them dry. They are packed in brine or oil, and both of those slow everything that follows.
2. Slice them into rings or at least halve them, but do not leave any whole. An intact olive has waxy skin all the way round and almost nothing can get out through it.
3. Blot the cut faces once more before they go on the tray. The flesh gives up a surprising amount of liquid the moment it is opened.
4. Lay the pieces cut side up on mesh with clear space around each one. Olives are oily and will slide into one another on a smooth tray.
5. Dehydrate at 57 °C for 8 hours. Expect the colour to deepen a long way — black olives go almost to charcoal and green ones turn khaki.
6. They are done when a piece is shrunken and leathery with no wet sheen on the cut face. For something crisp enough to crumble over a pizza, run them until a piece cracks under a fingernail.
7. Cool them spread out on a plate and blot them one last time. Olives sweat oil as the heat leaves them, and oil on the surface is what turns a jar rancid early.
8. Keep them in an airtight jar in the fridge for three months, or in the freezer beyond that. They are the one dried product here that does not belong in a warm cupboard, because the oil is inside the fruit and cannot be taken out.