Tonic water

Under ultraviolet light, the quinine in tonic water fluoresces.

Tonic water (or Indian tonic water) is a carbonated soft drink, in which quinine is dissolved. Originally used as a prophylactic against malaria, tonic water usually now has a significantly lower quinine content and is consumed for its distinctive bitter flavour. It is often used in mixed drinks, particularly in gin and tonic.

History

The drink gained its name from the effects of its bitter flavouring. The quinine was added to the drink as a prophylactic against malaria, since it was originally intended for consumption in tropical areas of South Asia and Africa, where the disease is endemic. Quinine powder was so bitter that British officials stationed in early 19th Century India and other tropical posts began mixing the powder with soda and sugar, and a basic tonic water was created. The first commercial tonic water was produced in 1858. The mixed drink gin and tonic also originated in British colonial India, when the British population would mix their medicinal quinine tonic with gin.

Since 2010, at least four tonic syrups have been released in the US. Consumers add carbonated water to the syrup to make tonic water; this allows drinkers to vary the intensity of the flavour.

Quinine content

Medicinal tonic water originally contained only carbonated water and a large amount of quinine. However, most tonic water today contains a less significant amount of quinine, and is thus used mostly for its flavor. As a consequence, it is less bitter, and is also usually sweetened, often with high fructose corn syrup or sugar. Some manufacturers also produce diet (or slimline) tonic water, which may contain artificial sweeteners such as aspartame. Traditional-style tonic water with little more than quinine and carbonated water is less common, but may be preferred by those who desire the bitter flavor.

In the United States, the US Food and Drug Administration (FDA) limits the quinine content in tonic water to 83 ppm (83 mg per liter if calculated by mass), while the daily therapeutic dose of quinine is in the range of 500–1000 mg, and 10 mg/kg every eight hours for effective malaria prevention (2100 mg daily for a 70 kg adult). Still, it is often recommended as a relief for leg cramps, but medical research suggests some care is needed in monitoring doses. Because of quinine's risks, the FDA cautions consumers against using "off-label" quinine drugs to treat leg cramps.

Uses

Tonic water is often used as a drink mixer for cocktails, especially those made with gin or vodka (for example, a gin and tonic). Tonic water with lemon or lime flavour added is known as bitter lemon or bitter lime, respectively. Such soft drinks are more popular in the United Kingdom and Europe than in the United States.

Fluorescence

Tonic water will fluoresce under ultraviolet (UV) light, owing to the presence of quinine. In fact, the sensitivity of quinine to UV is such that it will appear visibly fluorescent in direct sunlight.