Combine 1/2 cup water and 1/2 cup granulated sugar in a small saucepan. Add the whole allspice berries, whole cloves and 1/4 tsp ground cinnamon. Bring to a gentle simmer over medium heat, stirring to dissolve the sugar. Simmer for 5 minutes to extract spice flavors, then remove from heat and let steep for 15 minutes.

Strain the syrup through a fine mesh sieve to remove the whole spices and any sediment. Cool to room temperature. This yields about 3/4 cup allspice syrup. Store any excess in the refrigerator for up to 2 weeks.

Soda Base

Make brown sugar syrup (if not using pre-made)

If you don't have brown sugar syrup, make quickly by combining 1 cup packed dark brown sugar with 1/2 cup water in a small saucepan. Warm over low heat, stirring until sugar dissolves. Cool before using. (Recipe above assumes you have 1/2 cup ready.)

Prepare citric acid solution

To mimic cola brightness, dissolve a very small amount of citric acid: mix 1/8 teaspoon citric acid with 2 tablespoons warm water, then dilute so you use about 1/4 teaspoon of this solution (approximately 0.25 tsp) in the final drink. If you prefer lemon, substitute 1/2 tsp fresh lemon juice.

Assemble the Mr. Pibb-style soda

In a large pitcher combine 3 cups chilled carbonated water with 1/2 cup brown sugar syrup, 1 tablespoon caramel syrup, 1/2 teaspoon vanilla extract, 2 teaspoons of the cooled allspice syrup, 1/2 teaspoon light molasses, and the prepared citric acid solution (or 1/2 tsp lemon juice). Stir gently to combine — avoid vigorous stirring to keep carbonation. Taste and adjust: for more spice, add up to 1/2 tsp more allspice syrup; for more sweetness, add up to 1 tablespoon extra brown sugar syrup; for more tang, add small drops of the citric solution.

Chill and serve

Fill a tall glass with ice (optional). Pour the assembled soda over the ice. Garnish with a lemon wedge if desired. Serve immediately for best carbonation and flavor.