Tonic Water Recipe

Prepare citrus and botanicals

Wash the lemons, limes, and orange thoroughly. Using a microplane or vegetable peeler, remove the zest from the fruits, avoiding the white pith as much as possible. Lightly crush the cardamom pods with the flat side of a knife. Measure out the cinchona bark, coriander seeds, juniper berries (if using), and bitter orange peel.

Simmer extraction

Combine the cinchona bark, citrus zests, crushed cardamom, coriander seeds, juniper berries, and bitter orange peel in a medium saucepan with 4 cups of water. Bring to a gentle simmer over medium heat. Do not boil vigorously — simmer at low heat for 20–25 minutes to extract quinine and aromatic oils. Stir occasionally and keep the pot partially covered to limit evaporation.

Steep and strain

After 20–25 minutes, remove from heat, cover fully, and let steep for an additional 30–45 minutes to maximize flavor extraction. Once cooled enough to handle, strain the liquid through a fine-mesh sieve lined with cheesecloth into a heatproof bowl or measuring cup, pressing gently on solids to extract as much liquid as possible. Discard solids (or reserve for another infusion if desired).

Acidify

While the strained extract is still warm, stir in the citric acid until dissolved. Taste carefully and adjust acidity by adding up to 1/2 tablespoon more citric acid if you prefer a brighter, tarter tonic.

Make simple syrup

Return the flavored extract to a clean saucepan. Add the granulated sugar and brown sugar. Warm gently over low heat and stir until the sugars are completely dissolved, about 5–8 minutes. Do not boil — the goal is to create a clear syrup that captures the flavor, not caramelize it.

Adjust sweetness

Taste the syrup once sugars have dissolved. The syrup should be noticeably sweet but balanced with bitter and citrus notes. If it is too bitter, add up to 2 tablespoons more granulated sugar; if too sweet, add a teaspoon of citric acid or a squeeze of fresh lemon juice and stir to combine.

Make tonic concentrate

Allow the flavored syrup to cool to room temperature. Pour the cooled syrup into a clean bottle or jar and add 8 cups of cold water to dilute the concentrate. Shake or stir to combine thoroughly. This yields a lightly flavored tonic concentrate; final sweetness and bitterness should be slightly stronger than desired for drinking because it will be diluted further with carbonated water.

Chill and carbonate

Refrigerate the tonic concentrate until cold, at least 2 hours (overnight recommended for best integration of flavors). To serve, mix 1 part tonic concentrate with 3 parts chilled carbonated water (adjust ratio to taste). Fill a glass with ice, pour 1 cup carbonated water over ice, then slowly add about 1/3 cup concentrate (or mix in a separate pitcher) to avoid losing carbonation. Stir gently once.

Serve

Garnish with a thin slice of lemon or lime wedge if desired. Use as a mixer for gin, vodka, or enjoy on its own. Store concentrate refrigerated for up to 2 weeks.