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Research note 033 — 2026-09-04

Andes Made 'Inedible Bitterness' a Staple

The Andean highlands hold two records of plants too bitter to eat as they are, turned into a staple or a preserved food. One is chuño and tunta, preserved foods finished from native bitter potatoes (papa amarga) by freezing and river soaking. The other is lupin beans (tarwi, Lupinus mutabilis), which contain bitter alkaloids and are finished by water treatment. In the wording of the material itself, the purpose of both processes is to "remove the bitterness." This note traces their standard definitions and process chains using only what is recorded by Peru's national standards, a producers' field guide from the Puno region, and a review paper on seed composition.

What this page establishes

• The process for making tunta and chuño from native bitter potatoes is recorded step by step in Peru's national standard and in a producers' field guide.
• The explanation that prolonged river soaking washes out the bitter compounds is recorded as a narrative passed down among producers and technicians, but verification by chemical analysis has not yet been confirmed.
• One source reports that water treatment and boiling remove 89-97% of the alkaloids from bitter lupin (tarwi) seeds.
• A path to reducing bitterness through breeding, such as the low-alkaloid cultivar 'Inti,' is recorded, but a combined cultivar that resists insect damage while keeping only the seed's bitterness low remains at the proposal stage.

Bitter Potatoes Have a Name in the Standard

Peru's national standard defines Andean potatoes by dividing them into three categories: native bitter varieties, native sweet varieties, and improved varieties. The bitter varieties are called papa amarga, a category in the standard that groups together several native cultivar groups.

The preserved food itself, made from this bitter potato as its raw material, is also defined by the standard together with its process. Tunta is recorded as a food made through a sequence of dehydration steps: multiple rounds of freezing, soaking in flowing water, and sun-drying.

A Chain of Freezing, Soaking, and Drying

A field guide for producers in the Ilave river basin, Puno region, records this dehydration process broken down further into 10 steps: receiving, sorting and classifying, first freezing, soaking in water, second freezing, peeling and washing, drying, rubbing and winnowing, sorting and packing, and storage.

The first freezing is carried out by exposing the potatoes to low nighttime temperatures below 5℃ for 3-4 nights. It is recorded that the period chosen for this is May-July, calledépoca de heladas (frost season), when climate conditions of strong sunlight, low humidity, and little cloud cover align.

The frozen potatoes are next submerged inside an enclosure built from netting and stakes, and soaked in flowing river water for 21-30 days (some reports give an average of about 25 days). It is also recorded that their position is moved every 5 days.

For the finishing peeling and for lifting the potatoes out of the river, it is recorded that dedicated tools with local vocabulary are used, such as the large strainerwiscaña (iron-ring diameter 50cm) and the netted clothtaquiña, used for peeling by treading pressure.

Chuño, a very similar preserved food, differs from tunta in both color and process when the two standards' definitional texts are compared. Chuño is a dark-brown dehydrated potato made by repeating freezing and sun-drying without peeling, and the standard's definitional text contains no mention of the prolonged river-soaking process that is central to tunta.

Washing Out Bitterness: A Narrative, and What Came After

The field guide for producers and technicians also records a narrative about why such a laborious river-soaking process is carried out at all. It holds that tunta was once made only from native bitter varieties (papa amarga), and that prolonged soaking in the river washed out the glicoalcaloides (glycoalkaloids), making its consumption possible.

This narrative is preserved not as a quantitative demonstration of the washing effect through chemical analysis, but as a record shared between producers and technicians. Even so, the flavor of good-quality tunta itself is described asagradable, ligeramente insípido (pleasant, slightly bland), and it is recorded as having a quality of absorbing the flavor of whatever ingredients it is cooked together with.

Meanwhile, a processing evaluation carried out across several production modules, including the improved cultivar silver, also reported that aligero amargor bastante insignificante (slight, fairly insignificant bitterness) was detected. Even after going through such a laborious process, the bitterness is not necessarily reduced to zero.

Lupin (Tarwi) Also Has Bitter and Sweet Varieties

Alongside the potato, another candidate for an Andean bitter staple is the lupin bean (tarwi,Lupinus mutabilis). The bitter alkaloids contained in this species' seeds are a group of compounds called quinolizidine alkaloids (QA), and a distinction is recorded in which sweet cultivars have total QA <500 mg/kg while bitter cultivars have >10,000 mg/kg. ForL. mutabilis, there is 1 paper reporting a value of total QA 31,000 mg/kg.

Among the seed's QA composition, the compound lupanine is recorded as accounting for the largest share (47–58%), followed by sparteine (7.4–16%) and 13α-OH-lupanine (7–15%).

To remove this bitter alkaloid, soaking in salt water and washing has traditionally been carried out. A process combining water treatment and boiling is reported to remove 89–97% of the QA in the seed; biological, chemical, and aqueous methods all exist, and a process finishing in as little as 1 hour is also recorded. Another source notes that soaking and heating alone also lower the alkaloid content, and that following it with microbial fermentation lowers it further, though results are not consistent across strains and species.

Cultivar breeding is also recorded as another path for managing bitterness. The low-alkaloid cultivar 'Inti', bred through reselection in the early 1980s, was recorded in Gross et al. 1988 with a value of alkaloid content under 0.02%.

In breeding programs for the closely related species Lupinus angustifolius, there is a more far-reaching proposal. It is a description proposing, as a future breeding goal, a combined 'bitter/sweet' phenotype that keeps a high alkaloid concentration in the leaves and stems to prevent insect damage, while keeping the alkaloid concentration low only in the seed.

What is not known

• The total QA figure of 31,000 mg/kg for L. mutabilis is a single report, and whether it can be generalized to other cultivars or growing regions cannot be determined within the scope of this ledger.
• The staged decline in debittering (soaking/heating alone, then followed by fermentation) is a secondary organization by a review, and the statistical tests and sample sizes of each primary study are not fully shown within the review. The review itself also states that it cannot explain the inconsistency arising from strains and process conditions.
• The number of steps in the tunta process differs by source, between 8 steps and 10 steps, and the descriptions of days and temperature also vary in range. Which should be regarded as the standard sequence cannot be decided within the scope of this ledger.
• The narrative that river soaking washes out glycoalkaloids is a record shared among producers and technicians, and quantitative verification by chemical analysis is not included in this ledger.
• How widely the low-alkaloid cultivar 'Inti' is currently adopted cannot be confirmed from this material.
• L. angustifolius's 'bitter/sweet' combined phenotype is a description at the proposal stage, and does not indicate an already-realized registered cultivar.

Frequently asked

How do tunta and chuño differ?

Both tunta and chuño are processed foods that turn native bitter potatoes into a preserved food, but their standard definitions differ in both color and process. Chuño is a dark brown preserved potato made by repeating freezing and sun-drying with the skin left on, and the standard's definitional text does not mention a river-soaking process. Tunta is a white food made through multiple rounds of freezing plus soaking in flowing water and sun-drying, and this river-soaking step is what distinguishes it from chuño in the definition. Both are comparisons of definitional text in standards documents, not reports of directly observed processing differences in the field.

How is the bitterness removed from bitter lupin beans (tarwi)?

The traditional method recorded is soaking and washing the seeds in salt water. One review reports that a process combining water treatment and boiling removed 89–97% of the alkaloids contained in the seeds. Soaking and heating alone also lower the alkaloid content, and following that with microbial fermentation lowers it further, though the same review also notes that results are not consistent across strains and bean types. A process taking as little as 1 hour has also been reported, but the details of the conditions could not be fully traced within the scope of this material.

Related:Andean lupin / narrow-leafed lupin / lupanine / lupin debittering / Tunta / Chuño / Tunta and chuño processing
Related research notes: A World Map of Debittering / How Bitterness Gets Institutionalized
Source ledger: the source ledger