Wash the rhubarb thoroughly before peeling it. Measure the peel and place it in a pan. Add the rest of the ingredients and bring everything to a boil.
Cook: Turn the heat down to low and let the syrup cook, uncovered for 20-25 minutes, depending on the pot you are using. If the pot is very wide, the cooking time is shorter. The liquid should be slightly thickened, but not too thick.
Rest: Take the pot off the heat, let cool down and keep in the fridge or cellar for 24 hours.
Strain the syrup and discard the peel.
Cook again: Pour the syrup back into the clean pot, bring to a boil and simmer, uncovered for 6-8 minutes.