Tunta and chuño processing

In the Andean highlands of the Altiplano on the Peru–Bolivia border, above 3800 meters, a traditional technique continues to process potatoes into dehydrated potatoes (tunta/chuño/moraya) through a sequence of selection, freezing, river immersion, refreezing, peeling, and sun-drying. Peru’s national standard NTP 011.400 (2007) formally defines the "tunta" produced by this process as a rough-surfaced, white dehydrated food obtained through repeated freezing, immersion in flowing water, and sun-drying. Because the process depends on winter nights below freezing and strong sunlight, it is carried out only in limited seasons and at limited elevations.

A public guide (2008) describing producers’ practice in the Ilave River basin of Puno organizes tunta processing into 10 stages: receiving, selection, first freezing, water immersion, second freezing, peeling and washing, drying, rubbing and winnowing, selection and packing, and storage. By contrast, the background account in a 2021 paper on the same southern Peruvian highlands lists 8 stages: selection, initial freezing, fermentation immersion, peeling, wet fermentation, heat drying, quality selection, and storage. Sources differ on whether wet fermentation is an additional step and on the stated durations (3–4 nights versus 3–8 nights for initial freezing; 21–30 days versus 15–30 days of immersion plus a separate 21 days of wet fermentation). The basic structure of freezing, immersion, and drying is shared.

The first freezing is performed by exposing the potatoes to night temperatures below 5°C for 3–4 nights. Winter from May through July, called 「época de heladas(氷結期)」 (in translation: "frost season"), combines strong sunlight, low humidity, and little cloud cover, conditions described as supporting natural freezing and drying. A 2023 empirical study also records a similar first-freezing procedure of leaving the raw potatoes in an environment below 5°C for 3–4 nights.

The frozen potatoes are submerged in river enclosures made of nets and stakes, "jaula" and "poza", in a clear, gently flowing area for 21–30 days depending on variety (one report gives an average of about 25 days), and moved every 5 days. The steps are documented together with local tool names: a large strainer with a 50 cm iron frame called "wiscaña" for lifting the potatoes, "chuñahuis" for the open area used in freezing and drying, and a net-like cloth called "taquiña" for peeling by treading.