In any neighbourhood market in this region there is a heap of small, grey, wrinkled things, hard as stones, piled up next to the fresh potatoes. They are sold loose, they cost little, and almost no traveller asks what they are.
They are freeze-dried potatoes. And not metaphorically: genuinely freeze-dried, frozen and dehydrated, by the same physical principle modern food industry uses, except that here the process is done by the climate and has been working for thousands of years.
01 What it actually is
Chuño is a preserved potato product, traditional among the Quechua and Aymara communities of Peru and Bolivia, and known in Chile and northwest Argentina too. Its name comes from Quechua ch'uñu, meaning frozen potato; in the dialects of the Junín region it means wrinkled.
It is not made with just any potato. Bitter, frost-resistant varieties are used, unpleasant to eat fresh, and precisely for that reason they find their use here. The raw material is not the good potato: it is the one left over.
And it has a date. It is made at the beginning of winter, in June and July, when temperatures reach around five degrees below zero at altitudes above 3,800 metres. The potatoes are selected after the April–May harvest, and small ones are chosen because they are easier to process.
02 The five days
The process starts by spreading the potatoes close together on flat ground and leaving them in the open. At night they freeze with the cold of the high plateau; by day they dehydrate in the sun. That alternation is repeated for about three nights.
The effect is exactly that of freeze-drying: the ice forming inside breaks the cell walls, and with the walls broken the water comes out far more easily. The freezing does not preserve the potato: it prepares it.
They are then taken to flat areas called chuñochinapampas, a term of Aymara origin translating as the place where chuño is made. And there comes the part that sounds implausible until it is explained: they are trodden on.
Whole families build small piles with their feet and dance on them. That removes what little water is left and strips the skin; what does not come away is removed by hand afterwards. They are then left to rest for over a week, depending on how the weather behaves.
03 White and black
From there the path forks. Black chuño comes straight out of the freezing, treading and refreezing process: it is not washed or wetted again, simply sun-dried. It is the one most likely to stay in the farmer's own house.
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White chuño is obtained by washing the frozen potatoes, and there are regional variants. In Peru they are taken to a river and left in pools for about a week; in Bolivia they are spread on blankets or straw and constantly sprayed with water. The final step is drying them in the sun.
The result is also known as papas secas, and in Bolivia it goes by the name tunta. It is the more commercialised of the two, and the one you see piled up in the big markets.
04 Decades in a sack
Once dried, and with minimal care in storage, the product lasts an extremely long time: storage over decades has been documented. With no refrigeration, no vacuum packing and no preservatives.
It is worth pausing on what that solves. In a region where farming depends on an annual cycle and where a bad harvest means a whole year of trouble, having a larder that keeps for decades is not a convenience: it is insurance.
05 The empire hypothesis
Chuño predates the thirteenth-century Inca empire. The product has been found at several archaeological sites, among them Tiwanaku, on the Collao plateau, an area today split between Peru and Bolivia. The chronicler José de Acosta described it as early as 1590.
Because it is easy to carry, keeps a long time and is nutritious, Inca soldiers ate it on the march. It is, in practice, a field ration: light, imperishable and needing only hot water to become food again.
From that comes a thesis worth telling carefully, because it is an interpretation and not a proven fact: the geographer Carl Troll argued that the sub-freezing night temperatures of the southern Peruvian highlands, by making chuño production possible, favoured the rise of the Inca empire.
Whether or not it is the full explanation, the idea is powerful and useful for looking at the landscape differently. An empire that stretched across thousands of kilometres of mountains needed to move food, and here was a way of preserving it that depended on nothing but altitude.
06 Where to see it and how to eat it
You do not need to look for it anywhere special: it is in the produce markets, piled up loose. And it is eaten in many forms, from desserts to cooked dishes, as well as chuño flour, an essential ingredient in many Peruvian recipes.
The most common way you will meet it is in soup. Jakonta is made with whole chuño, and chairo, one of the most traditional Bolivian soups, uses ground chuño along with meat and vegetables. It is also traditional in southern Peru, in Arequipa and Puno.
And a warning to avoid disappointment: it is not a potato. In Bolivia it is expressly stressed that the two are not the same, and in certain recipes they cannot be swapped. Chairo, for instance, is not considered chairo without ground chuño: the other ingredients can be substituted, that one cannot.
One idea stays with you from here. We are used to thinking that preserving food requires a machine: a fridge, a freezer, an industrial freeze-dryer. In these Andes the machine is the place itself, and it works two months a year.
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