Two tall glasses of pale straw-colored vermouth and tonic packed with ice, fine bubbles rising, a long curl of lemon peel in each, beside a small bowl of bright green olives

Vermouth and Tonic, and Why the Tonic Chooses the Vermouth

September 30, 2026

Pour a dry vermouth over a glass packed with ice, fill it with cold tonic, twist a strip of lemon over the top, and you have one of the easiest good drinks there is. It is long and pale, bitter at the edges, about as strong as a beer, and quick enough to make while guests are still taking their coats off. There is one trap, and it is sugar. Tonic water carries real sugar, and with a dry vermouth both tonics compared below bring more of it to the glass than the vermouth does. That decides which vermouth goes under it.

This drink is a close relative of the vermouth and soda recipe, but the two lengtheners behave differently. Soda water only dilutes. Tonic adds sweetness and bitterness of its own, which changes the vermouth you want under it.

Where the sugar comes from

Vermouth is wine that has been flavored with wormwood and other botanicals, fortified with added alcohol and, usually, sweetened. European law requires at least 75 percent of the volume to be wine or other grape products and sets the actual alcohol at no less than 14.5 and under 22 percent. The same law ties the sweetness words on the label to numbers: extra dry means under 30 grams of sugar per liter, dry means under 50, and sweet means 130 or more.

Tonic brands vary a lot in sugar, so the nutrition panel on your own bottle is the number to trust. As a benchmark, the USDA's standard entry for tonic water lists 8.8 grams of sugar per 100 grams. Fentimans lists 4.4 grams per 100 ml, so with it every number in the tonic column is roughly halved. Here are the two set against each other in this recipe's serve of one part vermouth to two parts tonic, 60 ml and 120 ml:

Vermouth	Sugar from 60 ml of vermouth	Sugar from 120 ml of tonic (USDA benchmark)	The glass, per liter	How to pour it
Extra dry (under 30 g/L)	under 1.8 g	about 10.6 g	under about 69 g	Full tonic, lemon peel, an olive if you like
Dry (under 50 g/L)	under 3 g	about 10.6 g	under about 76 g	Full tonic, lemon or grapefruit peel
Bianco	Bianco is not one of the legal sweetness terms, so the word alone does not set the sugar. Taste it cold		depends on the bottle	Full tonic if it tastes dry, the sweet row if it coats your tongue
Sweet (130 g/L and up)	7.8 g or more	about 10.6 g	about 102 g or more	Half tonic, half soda water, orange peel

With a lower-sugar tonic such as Fentimans (4.4 g per 100 ml, about 5.3 g per glass), the glass totals fall to under about 40 g/L for extra dry, under about 46 for dry, and about 73 or more for a sweet rosso.

With an extra dry vermouth and a tonic at the USDA benchmark, more than 85 percent of the sugar in the glass comes from the tonic. Even with a lighter tonic like Fentimans it is about three quarters or more. With a tonic at the USDA benchmark, a sweet rosso poured the same way ends up at around 100 grams of sugar per liter or more, close to Coca-Cola, which has 39 grams in a 355 ml can, or about 110 per liter. That is why a rosso at full tonic can drink more like a soft drink than an aperitif, and why it is the tonic, not the vermouth, to pull back. Split the 120 ml into 60 ml of tonic and 60 ml of soda water and, with a benchmark tonic, the sweet rosso drops to roughly 73 grams per liter or more, about where a dry vermouth at full tonic tops out.

So the rule for this drink is to choose the vermouth for its smell and its bitterness, and let the tonic set the sweetness. That makes it a good place for a very dry bottle. For the tonic, a small bottle helps. Fentimans (shop Fentimans Tonic Water) comes in 200 ml bottles and lists juniper, kaffir lime leaf and lemongrass among its botanicals. One bottle fills a glass and most of a second, so little is left open to go flat.

Strength is the other reason this drink suits the early evening. The law allows vermouth anywhere from 14.5 to just under 22 percent, so the label is the place to check. At 16 to 18 percent, a 60 ml pour holds about 7.6 to 8.5 grams of alcohol, a little over half of the 14-gram US standard drink. In the 180 ml glass, before the ice starts melting, that comes to roughly 5 to 6 percent alcohol, close to the 5 percent the NIAAA uses for regular beer, with less alcohol than a can of one.

Ingredients, for four

240 ml (8 oz) dry, extra dry or bianco vermouth, refrigerated. An opened bottle belongs in the fridge anyway, and the vermouth storage guide explains why it fades once opened
480 ml (16 oz) tonic water, refrigerated and unopened: three 200 ml bottles
1 lemon, or a small grapefruit
Ice, enough to fill four tall glasses to the rim
Optional: grapefruit bitters such as Bittermens Hopped Grapefruit (shop Bittermens Hopped Grapefruit Bitters), or orange bitters such as Regans' No. 6 (shop Regans' Orange Bitters)
Optional, for extra dry vermouth: large green olives such as Bella di Cerignola (shop Bella di Cerignola olives)

Method

Chill everything first. Put the vermouth and the unopened tonic in the refrigerator for at least two hours. Temperature matters: in measurements on champagne, colder wine lost less dissolved carbon dioxide during pouring than warmer wine, and tonic, also a carbonated drink, is likely to behave similarly, though tonic was not part of the study. If there is room, put the glasses in the freezer for fifteen minutes.
Cut the peels before you open anything. Use a sharp peeler to take four wide strips of lemon or grapefruit peel, with as little white pith as you can manage. For long thin twists instead, use a channel knife (shop the Cocktail Kingdom channel knife). Once the tonic is open it should not sit around while you hunt for a knife.
Fill the glasses to the rim with ice. A 12-ounce Collins glass (shop Buswell Collins glasses) holds this pour with room for ice.
Measure the vermouth. Pour 60 ml into each glass, two pours from the small side of a 1 oz / 1.5 oz jigger (shop the Japanese-style jigger). Measure it, because the sugar balance in the table above only holds when the vermouth amount is fixed.
Add the tonic gently. Open the first bottle only now. Pour 120 ml into each glass down the inside wall, or let it run down the twisted shaft of a barspoon (shop the Leopold barspoon), rather than straight onto the ice. The same champagne study found that pouring down the side of a tilted glass kept more dissolved carbon dioxide than pouring straight down the middle. Give each glass one slow lift from the bottom with the spoon rather than stirring.
Add the peel, then taste. Hold a strip skin side down over the glass and pinch it. A fine spray of oil lands on the surface, and the citrus should reach your nose straight away. Rub the peel around the rim and drop it in. Now taste. If it is too sweet, add a splash of soda water. If it seems flat and one-note, add one dash of bitters. With an extra dry vermouth, an olive on a pick adds a salty note.

When the glass is wrong

What you taste	Likely cause	What to do
Like a soft drink with a bitter aftertaste	Sweet vermouth with a full measure of a high-sugar tonic	Pour a rosso with half tonic and half soda, or switch to a dry vermouth
Flat within minutes	Warm tonic, a bottle opened earlier, or a hard pour onto the ice	Cold, freshly opened small bottles, poured down the side
Too bitter	More tonic than a very bitter vermouth needs	Go back to 1 to 1.5 and use a wider strip of peel
Dull, sherry-like or slightly like cardboard	The opened vermouth has oxidized	Open a fresh bottle and keep it in the fridge

In Denver

Air pressure falls with height. Colorado State University Extension gives 14.7 pounds per square inch at sea level and 12.3 at 5,000 feet, and NASA's standard-atmosphere model puts Denver's 5,280 feet at about 82 percent of sea-level pressure. How much gas a carbonated drink gives off depends on how much dissolved carbon dioxide it holds compared with what the air pressure above it can keep in solution, so at lower pressure the same tonic starts out further from equilibrium. It is likely to foam more when opened and to lose its fizz somewhat faster, so steps 1 and 5 are worth extra care at 5,280 feet: small bottles, very cold, opened only when you pour. Other ways the altitude changes a kitchen are in the Denver altitude cooking guide.

Wine and bark, together since the 1600s

The drink is modern, but its two liquids go back a long way together. Quinine comes from the bark of the cinchona tree, native to western South America. Jesuit missionaries in seventeenth-century Peru took up the bark as a remedy for fevers, and it reached Europe as "Jesuits' bark." Chemists could not yet pull the active compound out of it, so it was usually dried, ground to powder and mixed into a liquid, very often wine.

One of the clearest records of this is a small book printed in London in 1682, The English Remedy: or, Talbor's Wonderful Secret. Robert Talbor was an English fever doctor who sold his secret cure to Louis XIV on the condition that it stay private until his death. When it was published, the secret turned out to be cinchona bark steeped in claret. The instructions call for a pound of the best bark, beaten to a fine powder and moistened with a decoction of anise and the juice of parsley, then covered with "as much good Claret Wine as the Vessel will hold" and left to steep for eight days.

In 1820 the French chemists Pierre-Joseph Pelletier and Joseph Bienaimé Caventou isolated quinine from the bark, and the pure drug gradually replaced the powder. Wine kept the flavor anyway. European law still has a category for it. Alongside vermouth, the regulation on aromatised wines defines "quinquina wine," a bitter aromatised wine whose main flavoring is natural quinine. A vermouth and tonic puts that old idea back together in a tall glass, with the wormwood from one side and the quinine from the other. The longer story of bitter medicines becoming bar ingredients is in the history of bitters article.

Worth knowing when the glasses go out

The tree's name rests on a legend. The genus Cinchona is named for the Countess of Chinchón, wife of a viceroy of Peru, who according to the famous story was cured of fever by the bark in the 1630s. A 2026 historical review in the CDC journal Emerging Infectious Diseases says most researchers now consider the story apocryphal, and Cambridge University Library's history of cinchona reaches the same conclusion. The name stuck regardless.

The quinine in tonic is a trace. The FDA caps quinine in carbonated drinks at 83 parts per million and requires the label to declare it prominently. At that ceiling, a 200 ml bottle holds at most about 17 milligrams. The prescription malaria dose on the Qualaquin label is 648 milligrams of quinine sulfate, which equals about 538 milligrams of quinine, every eight hours. One dose would take more than thirty small bottles, about six and a half liters of tonic. The quinine is there for the bitterness.

It glows. Quinine is fluorescent. It absorbs ultraviolet light and gives it back as blue light around 450 nanometers, which is why a glass of tonic glows pale blue under a black light. Chemistry classes use it to teach fluorescence. At a party, it just looks good.

Other ways to pour it

For a sweet rosso, use orange peel, split the lengthener between tonic and soda water (shop Fentimans Soda Water), and add a dash of orange bitters if the glass needs an edge. With extra dry vermouth, a lemon peel and an olive make the drink taste almost like a very long, very light martini. An anchovy-stuffed olive (shop Espinaler anchovy-stuffed olives) goes a step further, and the Spanish vermut hour guide covers the tradition behind it. Grapefruit peel and a dash of grapefruit bitters suit a dry vermouth with plenty of herbal character. The cocktail bitters guide explains why a single dash makes such a difference.

Put something salty on the table before the first pour: olives, salted almonds (shop Omnom sea-salted almonds), and olive oil potato chips such as Torres (shop Torres olive oil chips). For more on the carbonation side, Dave Arnold's Liquid Intelligence covers temperature, sugar and carbonation in cocktails (shop Liquid Intelligence). The Ambrosian Pantry is at 263 Josephine Street in Cherry Creek, Denver, and products ship nationwide from theambrosianpantry.com.