Homemade Tonic Syrup with Cinchona Bark

Before you start

Tonic water gets its bitterness from quinine, an alkaloid found in the bark of the cinchona tree. A homemade tonic syrup simmers cut cinchona bark with citrus peel, lemongrass and spices, then sweetens the strained liquid so you can mix it with soda water to your preferred strength. The result is amber rather than clear, with more citrus and spice than commercial tonic.

Two decisions make the difference. Buy cut bark rather than powder, because powdered bark is extremely hard to filter and leaves a muddy, overly bitter syrup. And keep the bark quantity modest: the goal is a pleasant bitterness, not a medicinal one, and homemade preparations are less predictable than commercial tonic. Patience with filtering pays off, since the fine sediment settles over time and can be decanted away.

Ingredients

• 750 ml (3 cups) water
• 10 g (about 2 tbsp) cut cinchona bark — not powdered; from a reputable spice supplier
• 2 limes, zest and juice
• 1 lemon, zest and juice
• 1 orange, zest only
• 2 lemongrass stalks — trimmed and chopped
• 1 tsp allspice berries — lightly crushed
• 10 g (2 tsp) citric acid
• ¼ tsp fine salt
• about 350 g (1¾ cups) granulated sugar — or 300 ml light agave syrup

Method

1. Combine the water, cinchona bark, citrus zests, lemongrass, allspice, citric acid and salt in a saucepan. Bring to a boil over medium-high heat.
2. Reduce to a gentle simmer, cover partially, and cook for 20 minutes. The liquid will turn reddish-brown and smell earthy and citrusy.
3. Remove from the heat and stir in the lime and lemon juice. Strain through a fine-mesh strainer into a tall jug, discarding the solids.
4. Let the liquid stand for 30 minutes so the fine bark particles sink. Pour it slowly through a coffee filter set in the strainer, leaving the sediment behind. Change filters as they clog.
5. Measure the filtered liquid; expect roughly 450 ml. Return it to a clean pan, add the sugar and warm gently, stirring, just until dissolved.
6. Cool, bottle and refrigerate. For a gin and tonic, combine 45 ml gin and 20 ml tonic syrup in a glass with ice, top with 100 ml chilled soda water and stir once.

Tips for success

• Start with 15 ml of syrup per drink and adjust. Bitterness reads differently once diluted with soda.
• Use a very cold, freshly opened soda water so the drink stays lively; the syrup itself adds no fizz.
• Let the bottled syrup rest overnight in the fridge and decant it off any new sediment before use.

Substitutions

Granulated sugar

Light agave makes a smoother, slightly less bright syrup that dissolves cold. Use about 300 ml.

Lemongrass

A teaspoon of dried lavender or a few strips of grapefruit peel change the aromatic profile.

Cinchona bark

There is no direct swap for quinine bitterness. Gentian root gives a different, earthier bitterness; use only 2 to 3 g.

Troubleshooting

The syrup is cloudy and gritty

Bark particles passed the strainer. Let it settle in the fridge and decant, or refilter through a fresh coffee filter.

The gin and tonic tastes too bitter

Use less syrup and more soda, or add a little simple syrup. Next batch, reduce the bark slightly.

It tastes flat and not citrusy

The zest included pith or the juice went in early. Add the juice after the simmer, and keep zest strips thin.

Storage

Refrigerate in a sealed bottle and use within about 3 to 4 weeks. Discard it if mold forms or it smells fermented.

Safety notes

Cinchona bark contains quinine, and the strength of homemade preparations varies. Keep the measured amount, do not concentrate the syrup further, and avoid it if you have been advised to avoid quinine. This is a cocktail ingredient, not a remedy.