Put the rye in a pan of boiling water and cook for about 1 hour until the grain cracks. Strain. Preheat the oven to 85°C (185°F). Spread the rye on baking trays and dry in the oven for 2 hours. Heat the oil in a saucepan to 185°C (365°F) and fry the rye until puffed and golden. Remove from the oil and drain on kitchen paper.
In an airtight container in a dry place for up to 6 days.