In a large sealable jar combine sugar and zest from grapefruit. Mash together to combine. Now, add grapefruit meat and vinegar. Chop 4 rosemary sprigs and add to jar. Add 2 last sprigs whole into jar. Mash all ingredients well to combine. Store in fridge for 2 days, stirring 2-3 times during the wait. When 2 days are up pour all ingredients through a fine mesh sieve into a jar your can pour into drinks from. Store in fridge.