Crush the dried allspice berries with a mortar and pestle. But not too much. You need coarse and large pieces, not a fine grind.
Add the Jamaican Rum and crushed allspice into a sealable jar and shake it before leaving it in a cold and dark place.
Let the mix sit for 4-5 days, and shake the jar once a day.
After 4-5 days, add the cinnamon stick(s) and anise pod to the mix. Shake again and let everything sit for another week.
Shake the jar from time to time to ensure that all spices are infused properly.
After seven days, strain the spiced Rum with the help of a sieve. Strain again with cheesecloth or coffee filter until all particles are removed.
Heat the water and Demerara sugar in a pan and stir the mix until the sugar has completely dissolved.
Take the syrup from the heat and let it cool down.
Next, combine syrup and allspice mix. Give it a shake, and let it sit for another two days in the fridge before using it in cocktails.