For the quince liqueur, peel the quinces and cut them into very small pieces, including the core. Boil sugar with 200 ml water, star anise, cinnamon sticks and clove heads without lid for 4 minutes bubbling on the stove.
Pour this syrup and 1500 ml water over the quinces and steam in the oven with the lid closed at 225° Celsius for about 1 1/2 hours. Leave overnight in the turned off oven. Then strain through a muslin cloth, mix with the grain and bottle the quince liqueur.