Instructions

1. Rinse the liver and pat it dry, then peel off the thin membrane on the outside if it comes away. It dries into a tough film that a dog will chew off and leave behind.
2. Firm the liver in the freezer for an hour before cutting. Fresh liver is soft enough to smear under a knife, and trying to cut it warm gives you ragged pieces of every size.
3. Cut it into thin strips and then into bite-sized pieces, sized to the dog rather than to the chopping board. Liver is rich, so these are meant to be small treats given a few at a time.
4. Sprinkle the powdered eggshell over the pieces once they are on the trays. It is calcium, and there is no liquid in this recipe to carry it, so it has to go on dry and stay where it lands.
5. Space the pieces so none touch and put a solid liner on the tray beneath. Liver weeps as it warms and the drips will mark every tray below it.
6. Dehydrate at 72 °C for 12 hours and run the machine somewhere ventilated. There is no polite way to put this: drying liver fills a house with a smell that stays for a day.
7. They are done when a piece cracks rather than bending and the broken face is a uniform dark brown with no red or shiny patch. Let them cool first — liver firms up considerably off the heat and a warm piece tells you nothing.
8. Store the cooled pieces in an airtight bag in a cool dark cupboard for two to four weeks, or freeze them for six months. Liver is rich in fat despite how lean it looks, and that fat is what turns, so trust your nose over the date.