Chop the firm flesh of ripe but not overripe pumpkins into cubes of a 1.5 cm (3/4 inch)
Put vinegar, sugar, lemon peel and spices into a pot and bring it to a boil.
Cook the pumpkin cubes in several portions until they are glassy through and through. This takes some time, about 20 – 30 minutes, depending on the size of the cubes. Make sure they are really cooked through, otherwise the preserve won’t last.
When the pumpkins are well cooked, put them out with a slotted spoon and put them into the jars.
Let the liquid boil for 5 minutes. Remove the lemon peel and pour the boiling-hot juice into the jars so that the pumpkin cubes are under the brim. Immediately tight-seal the lids.
Stored in a cool and dark place, sweet-sour pumpkin will last at least for one year.