The simplicity of a rasam is a decoy for its depth. At first sip, you may only discern the faint sweetness of a ripe tomato. Then comes the punch of tamarind. You reel momentarily from this affront, but you will soon be soothed by the nutty richness of mustard seeds fried in ghee — called the thalippu, or tempering that crowns this trellis of flavor.

For eons, South Indians of all stripes have claimed an intimate understanding of rasam, a broth (not unlike a stock) that teases complexity out of even the most minimal ingredients. At its simplest, this could mean a tomato or two, or a knob of dried tamarind and a scattering of spices — all allowed to commingle until their flavors merge into a cohesive whole.

Rasams are also made with other optional additions: souring agents, for instance, that lend the dish its characteristic tartness, including lemon, pineapple, green mango, and kokum, or the dried fruit of the Garcinia indica plant, among others. Occasionally they are enriched with cooked dal.

Depending on how you make it, this versatile brew can serve a number of culinary and social functions. Lightly spiced and mixed with mushy, overcooked rice, it becomes the perfect weaning food. Bolstered with an extra dash of ginger and pepper, it is an instant fix for an itchy throat. Cooked slowly and garnished with fresh cream, it acquires the opulence of festive food.

Yet, despite its treasured place in South Indian home cooking, rasam is rarely celebrated outside of that context. Usha Prabharakan, a 64-year-old cookbook author based in Chennai, decided to change that. In 1999, when her first cookbook, Usha's Pickle Digesta cult classic that features 1,000 recipes for Indian pickles — was still with the printers, she began laying the foundation for her second book: one that would document an equally staggering variety of rasams. Two decades later, after a five-year hiatus owing to serious health challenges, her forthcoming book, Usha's Rasam Digest, is nearly complete.

As expansive in scope and intricate in detail as its predecessor, Usha's Rasam Digest features a collection of 1,000 well-known and original recipes that straddle the similar yet distinct cuisines of the four southern Indian states. (While the dish is called rasam in Tamil Nadu and Kerala, it is known as saaru in Karnataka, chaaru in Andhra Pradesh, and saar in the western state of Maharashtra. There are minor differences between these versions, but the essence is largely the same).

In addition to geographical categorization, the cookbook also groups rasams according to complexity, seasonality, ingredients, unusual flavor pairings, and more. "If a vegetable, fruit, herb, or spice is in season, [the reader] can make a beeline for the ingredients and try out the rasams mentioned therein," Prabhakaran told me in an email interview. As testament to her commitment to the subject, some of the rasams in the book are so left-field, they're practically unheard of. For instance, under the aptly titled chapter "Unusual and Unanticipated Flavours," one finds a recipe for a watermelon rind-chow chow (or chayote) rasam, and another with cauliflower leaves and stems. In "Hard to Resist Residual Wonders," one learns how to spin a rasam out of leftover coconut chutney.

The sweeping scope of the book begs the question: Why would someone spend the better part of a decade-and-a-half in the active pursuit of a dish which, while loved, is not traditionally viewed as particularly rich in complexity? In her considered answer to this question, I get a glimpse of Prabhakaran's singular curiosity towards food. "I picked rasam for my second book because I have a case for it," she told me. "To this day, it hasn't ceased to amaze me."

This isn't just outsized affection. Although the origins of the dish are difficult to pin down, some believe that the word rasam is derived from the Sanskrit word 'rasa', which means essence, extract, or taste. According to food historian Colleen Taylor Sen, Ayurvedic principles may have contributed to a nuanced understanding of the importance of rasas or tastes in everyday dining. Ancient texts such as the Charaka Samhita, a foundational text on Ayurveda written in the 2nd century CE, and Sushruta Samhita, a treatise on medicine and surgery that dates back to roughly 700 to 600 BCE, underlined the importance of shadrasas or six tastes for good health.

"There are six basic tastes (rasas): sweet, sour, salty, bitter, pungent, and astringent," Sen writes in Feasts and Fasts: A History of Food in India. "A person's diet should contain all six to maintain balance and promote health, and most of India's cuisines include at least some of them." Given that food was intimately connected to medicine, it is plausible that the sweet-sour-salty-bitter composition of rasam was developed at least partially in adherence to these teachings.

According to Prabhakaran, at a more granular level, the ingredients that went into rasams were carefully chosen for their specific nutritive or digestive properties. "Ginger and black pepper are considered good for colds [and immunity], while tamarind and cumin enhance digestion. Coriander seeds have anti-inflammatory properties; mustard and fenugreek are antioxidants," she explains. To harness the potency of the spices, they are roasted and ground into a podi — a powdered blend that also sometimes includes a small amount of dal. This contributes both bulk and flavor to the dish.

Even though the principle of balancing the shadrasas through food may have been diluted with the passage of time, most rasams are a finely calibrated tribute to one or more of these tastes. Take the vepampoo rasam, for instance. The main ingredient of this rasam from Tamil Nadu are the dried blossoms of the vepam or neem tree. When fried in ghee and added to a tamarind-based rasam, the blossoms bring an aromatic and mellow bitterness to the dish. Or consider the purnam charu, a hearty rasam from Andhra Pradesh that features a filling of mashed chana dal, coconut, and jaggery, traditionally served as festive food. In this case, sweet and sour tastes are elegantly poised in counterpoint.

A rasam is therefore a feat of whittling many competing — and complementary — flavors down to their very essence. Deepa Reddy, an anthropologist based in Auroville (near Pondicherry) with an avid interest in food, says that this is both the charm and the challenge of the dish. "You have to build a scaffolding of ingredients, so that one little taste stands at the pinnacle," she told me.

The story of rasam's evolution becomes even more remarkable when you consider the fact that over time, it has seamlessly accommodated, and been shaped by, new influences and ingredients. The most significant of these is the tomato. Although the Portuguese are often credited with bringing tomatoes to India, it's likely that they didn't catch on until much later, during British colonial rule. In A Historical Dictionary of Indian Food, eminent food historian KT Achaya writes, "... unlike several other plants from the New World, the tomato did not come directly to India, but by way of England at a late but uncertain date perhaps around 1850."

According to Achaya, Niccolao Manucci, an Italian doctor, writer, and traveler who visited India in 1654, made mention of a brew that could well have been rasam. "In about AD 1700, Manucci noted that south Indians 'sip a concoction which is some water boiled with pepper'," wrote Achaya. This milagu-thanni (which means pepper-water in Tamil) was later adapted by British colonialists into mulligatawny soup, which was a meatier rendition of rasam, bolstered with chicken stock.

Although rasam is often thought of as a dish that celebrates vegetarian frugality, this perception was most likely shaped by powerful Brahminical notion of the superiority of vegetarian food habits. In practice, this perception has exerted significant cultural force throughout southern India. However, as Sen mentions in Feasts and Fasts, Ayurvedic physicians prescribed the consumption of meat for specific conditions. For instance, to treat consumption, Acharya Charaka, the author of the Charaka Samhita, recommended "chicken soup mixed with sour and pungent ingredients and flavoured with ghee," writes Sen. Could this have been the forerunner of a modern day kozhi rasam, a chicken broth that is popular in Tamil Nadu?

Over the last few months, amid the upheaval caused by a pandemic, food and its ability to provide comfort has become markedly more precious. Against this backdrop of a yearning for certainty and familiarity, comfort food has transformed from a catchphrase to one with profound cultural value.

For Deepa Reddy, whose anthropological interest in food finds vivid expression on Instagram, rasam was a good entry point into a deeper conversation about food. A couple of months ago, Reddy started a rasam series on Instagram. Some of the dishes she cooked as part of this series include a maavilai rasam, which uses a tea brewed of young mango leaves as its base. Soured with green mango, the rasam offers a new appreciation of astringency.

Reddy's initiative has sparked several others to contribute to the so-called rasam series. Through the series, I learned of dishes such as marunthu rasam, an almost medicinal brew made of long pepper, and the kulthi ka chaar or horsegram rasam made by the Dakhini Muslim community in south India. Given its adaptable nature, it seems particularly apt that rasam could inspire such a free-flowing exchange of knowledge, which otherwise often remains contained within cultural silos.

To Prabhakaran, who has brought an encyclopedic eye to this singular dish, the prospect of more people experimenting with rasam is an exciting one. It would mean a wider audience for a belief that she holds with the utmost conviction. "Rasam is a treat to the senses," she says. "More than a dish, it is an emotion."

This story was originally published on Food52.com: 1,000 Ways to Love Rasam — Southern India's Signature Peppery Broth