Place sorrel, smashed ginger, star anise and allspice in large pan.
Carefully add boiling water, 1 pint at a time, then stir.
Cover and allow to steep overnight.
When liquid is cool store in the fridge.
Once sorrel has steeped overnight remove from fridge and strain into mason jars.
Ensure that you have equal amounts of sorrel in each mason jar.
Grate remaining ginger into mason jars in equal parts.
Sweeten with your preferred sweetener and store for at least 1 hour.
To serve, add 2-3 dashes of bitters to each glass, shake up sorrel then strain into glasses on top of bitters.
Serve with or without ice.