Instructions

1. Seedless grapes are the only sensible choice, and thin-skinned varieties finish faster. Sultana and Thompson types are what commercial raisins are made from, for exactly this reason.
2. Pull the grapes off their stems and discard anything split or soft. A single fermenting grape will sour the ones lying around it on the tray.
3. Thirty seconds in boiling water is the whole blanch. It is not cooking anything — it cracks the waxy bloom so the water inside has a route out.
4. Chill them in ice water at once and drain. Left hot, a grape steams itself under its own skin and collapses.
5. Ten minutes in the citric acid solution keeps the colour from going black-brown. Skip it if dark raisins do not bother you, but do not skip the blanch.
6. Space the grapes so none are touching and expect a long haul — 30 hours at 57 °C is not an exaggeration.
7. Squeeze a cooled grape. A raisin is wrinkled all over and leathery and gives a little, with no juice appearing at the skin; cut one in half if you are unsure, because the surface misleads here more than on any other fruit.
8. Condition them a week in a jar you shake every day. These are among the most commonly pulled early, and the jar is where that turns up.
9. Sealed afterwards they hold a year in the cupboard. If they harden over the months, a few minutes in warm water or a splash of spirits brings them back.