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The Miller Library has other books on cinchona (the plant source of quinine), gin (from juniper), and various plant-based spirits, but Just the Tonic focuses on the evolution of this effervescent beverage, a journey from cinchona-derived medicinal preparations to treat fever, purportedly healthful restoratives for a host of ailments (the kombucha and CBD of earlier eras!), to a recreational beverage we still consume with or without spirits. Along the way, the authors touch on the history of malaria and its treatment, the effects of conquest and imperialism, how humans have harvested and stored ice since Mesopotamia’s tamarisk-lined icehouses of nearly 4,000 years ago, and so many other fascinating morsels of information. The book is profusely illustrated and captivatingly written by Kim Walker (a medical herbalist and historian of plant medicines) and Mark Nesbitt (curator of the Economic Botany Collection at Kew).

The Cinchona tree is native to the high-altitude cloud forests of the Andes, from Colombia south to Peru and Chile. It is a medium-sized evergreen tree with cinnamon-colored bark and loose flower clusters said to have a fragrance similar to lilac. It is the bark which was sought for its anti-malarial properties. However, malaria was not a documented ailment in South America until the Spanish conquest, which added population density to damp lowlands where mosquitoes thrive. 1633 marks the first known reference to use of the bark of the ‘fever tree'(arbol de calenturas) in the writing of a Peru-based Spanish priest, who noted that the bark could be dried, pulverized, and dissolved in a drink that would treat the fevers malaria causes. Eventually, the medicinal use of cinchona bark reached Europe. We tend to think of malaria as a tropical ailment, but marshy regions of western Europe harbor a less severe strain of the illness.

Cinchona bark is intensely bitter, so it was made palatable with port wine, herbs, treacle or syrup, citrus peel, and occasionally opium, in an assortment of proprietary formulations. (Advertisements for these are among the colorful illustrations in the book.) Where there is a market for a plant-based remedy, there is a motive for plant exploration, and this led to overharvesting and worker exploitation in South America. Plantations were also created in Java. But the amount of quinine present in the many species of Cinchona varies, and botanists had a challenge in telling species apart based on their dried bark. In the early 19th century, French chemists isolated two of the alkaloids found in the bark—cinchonine and quinine. This facilitated dosage measurement, an important thing, because too little is ineffective and too much is dangerous (even today there are instances of avid homebrewers developing cinchonism from an overdose of quinine).

Because of quinine’s toxicity and decreasing efficacy (the parasites were becoming resistant to it), there was a shift in the 20th century toward synthetic antimalaria drugs such as chloroquine (a name that may have a recent familiar ring to it!). Still, tonic water—like the Schweppes Bitter Lemon I remember drinking on hot days in Israel—remains associated with the eradication of malaria (though the amount of quinine in such drinks is minimal). For me, it conjured the history of Jewish immigrants draining swamps in the valleys and coastal plains of British Mandate Palestine. (By 1968, Israel was deemed malaria-free.)

The tonic water we know today was inspired by the popularity of visiting natural mineral springs, beginning in the times of the Roman Empire. Scientists in the 18th century strove to come up with a way to simulate this effervescence associated with healthful benefits by contrast with turbid swamp water), and gradually refined their devices for creating “bubbling scintillation” (see the illustration of an apparatus for “impregnating water with fixed air”) in a laboratory setting. Eventually, soda water became ubiquitous in soda fountains and grocery stores. These days, one can even make sparkling soda at the touch of a button, at home. Kew has created its own Royal Botanic Tonic and organic gin, and the book’s final chapter includes recipes for cocktails and mocktails. Bottoms up!