1 canned pineapple chunks, juice reserved
1/4 cup grapefruit juice
1/4 cup tarragon vinegar
2 Tbsp. light brown sugar
2 Tbsp. fresh dill, chopped
1 Tbsp. whole peppercorns
1/2 tsp. ground cinnamon
1/2 tsp. ginger powder
1 tsp. whole fennel seeds
Whisk all ingredients in a medium bowl until well blended.