Make a sugar solution from the sugar and the water.
Rub the yellow part of the grapefruit peel or peel it very thinly. Finely dice the pulp. Put the fruit pieces and the fruit bowl with vodka, coriander, cinnamon and sugar solution in a suitable container and mix. Close the jar tightly and leave to stand for 4 to 5 weeks.
Then strain the fruits and let the liqueur clarify for a week. If necessary, filter again before consumption.