Potatoes in the Inca Diet: Varieties, Chuño, and Storage

The potato (Solanum tuberosum) was the staple food of the highland Andes and the foundation of the Andean diet in the Inca Empire. The Incas cultivated thousands of distinct varieties of the potato, distinguished by the chronicler Pedro Cieza de León into some forty principal types and by the colonial administrator Felipe Guaman Poma de Ayala into a much more elaborate classification. Potatoes were grown at altitudes from 2,500 to 4,500 meters, with the highest-quality varieties cultivated above 3,800 m; the bitter varieties, which contain toxic glycoalkaloids, were reserved for the production of chuño — freeze-dried potatoes that could be stored for years without spoiling. Chuño was the principal form in which potatoes were stored in the state qollqas and in household trojes, and was the principal food distributed as famine relief and as military rations. The introduction of the potato to Europe after the Spanish conquest had a transformative effect on global food systems and remains one of the most consequential inheritances of Andean agriculture; the Inca food and agriculture of the empire cannot be understood without the central role of the potato.

Origins and the diversity of Andean potatoes

The cultivated potato was domesticated in the Andean region of present-day Peru and Bolivia at least by 8000 BCE, and possibly as early as 10,000 BCE, by the populations of the highland basins of Lake Titicaca and the Collasuyu. Archaeological excavations at the site of Tres Ventanas in the Lauricocha highlands, published by the ethnobotanist Donald Ugent in 1982, have established that the potato was cultivated in the central Andes by at least 7000 BCE; specimens from the Chiripa site in the Lake Titicaca basin, dated to approximately 1500 BCE, show clear evidence of selective breeding for larger tubers and reduced glycoalkaloid content. By the time of the Wari empire (c. 600–1000 CE), Andean farmers had developed perhaps 200 distinct varieties of the potato; by the time of the Inca conquest in the fifteenth century, the number had risen to perhaps 1,000 distinct varieties, of which the chronicler Cieza de León recorded some forty of the most important by name.

The diversity of Andean potatoes is a function of the extraordinary range of microclimates in the central Andes. Different varieties were bred for different altitudes, different soil conditions, and different resistance to frost, drought, and disease; the chroniclers record that the imperial administration used quipus to record the varieties cultivated in each province and the yields of each variety. The most comprehensive modern classification, developed by the International Potato Center (CIP) in Lima and published in the 1990s, recognizes seven species of cultivated potato in the central Andes: Solanum tuberosum (in two cultivar groups, the Andigena of the central Andes and the Chilotanum of southern Chile), S. stenotomum, S. phureja, S. ajanhuiri, S. juzepczukii, S. curtilobum, and S. × chaucha. Of these, S. juzepczukii and S. curtilobum are the bitter varieties, cultivated only for the production of chuño.

The bitter potatoes contain toxic glycoalkaloids (principally solanine and chaconine) at concentrations that render them inedible without processing. The Incas exploited the toxicity of the bitter varieties to produce chuño: the freeze-drying process that converts the fresh potato into a stable, edible product also breaks down the glycoalkaloids, rendering the chuño safe to eat. The bitter varieties, which were cultivated at altitudes above 3,800 meters where the sweet varieties grew poorly, had a substantial yield advantage over the sweet varieties, and chuño made from bitter potatoes was a substantial portion of the state reserves. The detailed treatment of Inca food and agriculture and of the vertical archipelago is given in the related articles.

Cultivation, harvesting, and the agricultural cycle

Potatoes were planted in the Inca agricultural system from August to November, depending on the altitude, and were harvested from March to May. The principal tool of cultivation was the chakitaqlla — a footplow consisting of a wooden pole about 2 meters long, tipped with a bronze or wooden point and fitted with a crossbar handle at the top and a footrest near the bottom. The chakitaqlla was used to break the soil of the potato fields, typically in conjunction with a yapa (digging stick) used to turn the soil. The chronicler Cieza de León recorded that the principal tool of the highland farmer was the chakitaqlla, and that a man using the chakitaqlla could break approximately 0.1 to 0.2 hectares of land per day.

The fields used for potato cultivation were of two principal kinds. In the lower-altitude valleys (2,500 to 3,500 m), potatoes were grown on andenes — terraced fields that retained moisture and prevented erosion. In the higher-altitude zones (3,500 to 4,500 m), potatoes were grown on puruma — open fields above the zone of permanent settlement that were cultivated for a few years and then allowed to fallow. The terracing system of the Incas was among the most extensive of the pre-industrial world, and the hydraulic engineering of the state was closely integrated with the agricultural cycle.

The harvest of potatoes was a major seasonal event. The hatun runa of the highland ayllus were mobilized for the harvest, and the work was typically performed in a system of ayni — the exchange of equal quantities of labor between households. The chronicler Cobo recorded that a typical highland ayllu would harvest its potato fields over a period of two to three weeks, and that the harvested potatoes were sorted by variety and by quality before being stored. The principal puruma harvests of the Collasuyu were performed in the early winter months of May and June, before the onset of the dry season, and the harvested potatoes were transported to the chuño fields of the waru waru raised fields of the altiplano.

Chuño: freeze-dried potatoes and the technology of preservation

Chuño — the freeze-dried potato — was the principal form in which potatoes were stored in the Inca state and one of the most important technical achievements of Andean agriculture. The technology of chuño production, as reconstructed from the chronicles of Cieza de León, Cobo, and Murúa, involved a sequence of three steps: a night of exposure to frost at high altitude, a day of exposure to strong sunlight, and a process of trampling to remove the skins and excess water. The process was repeated over a period of three to five days, after which the chuño was washed and dried for storage.

The best-quality chuño was produced from bitter potatoes at altitudes above 3,800 m, where the night-time temperatures in the months of June and July were reliably below -5 °C. The most important chuño-producing region of the empire was the altiplano around Lake Titicaca, and the principal chuño fields of the state were located near the provincial capitals of Tiahuanaco and Chucuito. The chronicler Murúa recorded that a single acre of chuño fields in the altiplano could produce approximately 5 metric tons of fresh potatoes, which after freeze-drying yielded approximately 1.5 metric tons of chuño. A similar ratio is reported by the Spanish chroniclers of the early colonial period, and the calculation is consistent with the modern experimental reconstructions performed by the CIP in the 1990s.

Chuño was stored in the state qollqas and in household trojes and could be kept for several years without spoiling. The state used chuño as the principal form of payment for the army and as the principal form of famine relief, and the chronicler Cieza de León recorded that the state qollqas of Huánuco Pampa held an estimated 30,000 to 40,000 tons of chuño and maize at any one time. Chuño was also an important item of long-distance trade, and the Qhapaq Ñan was used to transport chuño from the producing regions of the altiplano to the consuming regions of the central highlands and the Antisuyu lowlands. The detailed treatment of Inca storage and the qollqas is given in the related article.

Diet, nutrition, and the role of the potato in the Andean world

The potato was the principal source of calories for the Andean population and was the foundation of the daily diet. The chronicler Cieza de León recorded that a typical highland hatun runa consumed between 1.5 and 2.5 kilograms of chuño per day, together with smaller quantities of fresh potatoes, oca (Oxalis tuberosa), olluco (Ullucus tuberosus), and quinoa. The caloric yield of chuño was approximately 350 kcal per 100 grams, and a daily ration of 1.5 to 2.5 kilograms would have provided between 5,250 and 8,750 kcal per day — well above the daily requirement for an adult engaged in agricultural labor, and consistent with the chroniclers’ accounts of the substantial physical capacity of the Andean laborer.

The potato was also a substantial source of protein and vitamin C. Fresh potatoes contain approximately 2 percent protein and 20 mg of vitamin C per 100 g; chuño retains a substantial portion of both, although the vitamin C content of chuño is reduced by the freeze-drying process. The principal nutritional deficiency of the Andean diet was the limited supply of vitamin A, which the Incas attempted to address by the consumption of quinoa leaves and of the meat of cuy (guinea pig), both of which are rich in vitamin A. The detailed nutritional analysis of the Andean diet, based on the chroniclers’ accounts and on the modern nutritional studies, is given in John Murra’s The Economic Organization of the Inka State (1956) and in the more recent work of the anthropologist Rosaleen Howard-Malverde.

The potato after the conquest and its global diffusion

The introduction of the potato to Europe after the Spanish conquest had a transformative effect on global food systems. The Spanish brought the first potatoes back to Spain around 1570, and from Spain the crop spread to Italy, the Low Countries, and the German-speaking lands over the next century. The first clear illustration of the potato in European botanical literature appears in the herbal of Carolus Clusius, Rariorum plantarum historia (1601), which depicts a potato plant grown in the imperial gardens in Vienna from tubers obtained from the Low Countries. By the late 18th century the potato had become a staple of the Irish diet, and the failure of the potato crop in 1845–1846 — the Great Famine — caused the death of perhaps a million people and the emigration of another million.

The potato was, in this sense, a global inheritance from Andean agriculture. The Inca state, by the time of the conquest, had developed a sophisticated system of potato cultivation, processing, and storage that supported a population of perhaps ten million people in the highland Andes; the techniques of chuño production, in particular, allowed the Andean population to exploit a wider range of altitudes and a wider range of potato varieties than was possible in any other part of the world. The detailed treatment of Inca food and agriculture and of the Inca road system is given in the related articles; the waru waru raised-field agriculture of the altiplano, which was closely integrated with chuño production, is treated in the related article.