Thua nao
Also known as tua nao, tuanao, thua-nao, thua nao kab, Thai fermented soybean, northern Thai fermented soybean
Quick answer
Soybeans boiled and left for a few days to ferment without salt, the seasoning of northern Thai and Shan cooking. Savoury and strongly ammoniacal when fresh, it is mashed, pressed into thin discs and sun-dried to keep, and the dried disc smells roasted and nutty. It is soy, and so a declared allergen.
- Tastes of
- savoury, pungent, nutty, bitter
- Heat
- Scoville does not apply
Other names
What this spice is called elsewhere, and where the translation is not clean.
ถั่วเน่า
Thai — Northern Thailand
Romanised as thua nao, thua-nao and tuanao in the papers read. In Thai the word covers the fermented soybeans of every group in the north, though it is the Shan name; Karen and Lawa makers have their own.
โถ่เหน้า
Shan (Tai Yai), in Thai letters — Taunggyi, Shan State, Myanmar
The spelling a Thai-language study uses for the word as Tai Yai speakers in Taunggyi say it. The same study prints it in Shan script, which is not reproduced here because it could not be copied reliably.
Tor-Nor-Au
Karen — Pang Mapha district, Mae Hong Son
The fermented soybean of Karen makers in one village, made a little differently. Given in roman letters only.
Kuem
Lawa — Mae La Noi district, Mae Hong Son
The fermented soybean of Lawa makers in one village, boiled in the water left from cooking sticky rice. Given in roman letters only.
Each name is given as the source cited prints it. The Thai spelling is printed in the Thai abstract of a survey and throughout a Thai-language study of dish names.
Flavour and aroma
Savoury, with some bitterness, and not salty: it is made without salt, which the papers contrast with shrimp paste. A study read in abstract found both a starter-made and a naturally fermented thua nao far richer in free amino acids than the cooked beans, and attributed the bitterness mainly to the hydrophobic and basic amino acids and the savouriness mainly to the acidic ones.
One sample of Shan thua nao from a Mae Hong Son market held 10.77 mg of sodium per 100 g, which is what an unsalted bean would be expected to hold.
Strong, and described by those who study it in blunt terms. A review calls the ripe beans strongly ammonia-like and compares the traditional product to fish sauce; one group writes of a strong meaty aroma, another of a smell often described as pungent or rotten. The name carries the same idea: the review glosses thua as soybean and nao as spoiled. The dried disc smells different. In discs made in one laboratory the compounds that counted most towards the smell were grouped as green and fatty, nutty and roasted, sweet, sulphurous, woody and smoky, sour and fermented, and floral.
The first part is authors’ description and no panel’s. The groups for the dried disc were assigned from measured concentrations and published odour thresholds, with odour words taken from reference databases; nobody smelled the discs for that study.
Greyish brown when ripe, by one review’s description of the fermented beans. A storage study treated a strong dark brown as a sign of spoilage.
Descriptions by the authors. The colour measurements in the storage study are in tables that were not read.
Taste, smell and sensation, channel by channel
Smell, taste and the chemical sense of heat and cold are different senses. Each is listed with the compounds evidenced as producing it.
Smell
- Roasted — 2,5-Dimethylpyrazine
- Smoky
- Green
In dried discs made in one laboratory, the pyrazines were grouped as the nutty and roasted part of the smell, with 2,5-dimethylpyrazine the most abundant of them. Discs dried in the sun or in hot air held two to three times as much of it as discs dried under vacuum or by microwave. The grouping was worked out from concentrations and published odour thresholds, with odour words from reference databases; no panel smelled the discs.
The same study grouped 2-methoxy-phenol, which is guaiacol, as the woody and smoky part of the smell of the dried disc. The table puts it at roughly two and a half to four times as much in sun-dried and hot-air-dried discs as in microwave-dried and vacuum-dried ones. No smoke is involved in making thua nao.
A green, fatty note from the breakdown products of fat, hexanal above all, marked the sun-dried discs: hexanal was about twenty times higher in them than in discs dried by hot air or under vacuum, and several such compounds were found in the sun-dried discs alone.
Taste
- Savoury (umami)
Both a starter-made and a naturally fermented thua nao held much more free amino acid than the cooked beans they were made from, and the authors attribute the savoury taste mainly to the acidic amino acids. The abstract, which is all that was read, gives no figures.
- Bitter
The same authors describe a typical bitterness in thua nao and attribute it mainly to the hydrophobic and basic free amino acids. A review by the same group says the bitter-tasting amino acids made up more than half of the free amino acids, a figure it takes from a thesis not read here.
Sticky. The fresh beans are soft and carry a slight slime, which one paper compares to the stringiness of natto. The dried form is a thin, hard disc that is toasted or pounded before use.
The toasting and pounding of the disc are kitchen practice; the papers describe the disc and not how it is handled.
Heat
Pungency scale: none — this spice is not pungent
No heat.
- Ammonia — Released as the bacteria use the amino acids of the bean, and the source of the smell the product is named for. It rose through the three days of fermentation in five village batches.
- 2,5-Dimethylpyrazine — The most abundant pyrazine in dried discs made in one laboratory, at 3,568 to 11,097 micrograms per kilogram according to how they were dried, and named in an abstract as a predominant volatile of both starter-made and naturally fermented thua nao. Its odour is described as nutty.(what 2,5-dimethylpyrazine is)
- 2-Methylbutanoic acid — The most abundant of the branched volatile acids in the same dried discs, at 37,090 to 51,842 micrograms per kilogram, with an odour described as pungent, cheesy and sweaty. An earlier study, read in abstract, names it among the main volatiles of fermented beans.
- Free amino acids — Much higher in thua nao than in the cooked beans, and the source of its savoury and bitter taste according to the authors of the one study, read in abstract.
- Hexanal — A green, fatty-smelling product of fat oxidation: about twenty times higher in sun-dried discs than in discs dried by hot air or under vacuum in one laboratory comparison.
The concentrations are from one laboratory’s discs of black soybean thua nao made with a starter culture, and are relative concentrations by its method. The ammonia finding is from the text of the village study, whose table of figures was not read.
Pairings
Ranked by how well established the combination is, with the reason and the caveats attached.
Other spices and blends
Salt
ClassicThua nao is fermented with no salt at all, so the salt is added when it is used. A review by Thai food scientists says the ripe beans are eaten as they are or mixed with chillies, onions and salt, and a study of pe poke, the same kind of bean across the border in Myanmar, describes it mashed with salt and hot pepper before it is pressed into wafers and dried.
How: Fresh thua nao mashed with chilli, onion and salt
Add alongside: Onion
The catalogue does not yet cover Shan or Burmese cooking, so this is placed under Thai cooking alone. The practice is recorded on both sides of the border.
Preparation and use
Toast a dried disc over a flame or in a dry pan until it darkens and smells nutty, then pound or crumble it into the dish. Steam or roast the fresh beans before eating them. Salt the dish yourself: thua nao brings none.
A seasoning first and a food second. Thai food scientists describe it as a condiment, as a seasoning or flavouring enhancer, and as an ingredient that adds flavour to cooked dishes, serving chiefly in that role or mixed into chilli pastes and not eaten plain as natto is. The fresh beans are steamed or roasted, seasoned with chillies, onions and salt and eaten with sticky rice; the dried discs go into cooked dishes. In Tai Yai cooking it is the main seasoning, where Lanna cooking more often uses fermented fish or crab paste, and Tai Yai people in Taunggyi named a dish of mushrooms simmered with it. In kitchen practice the dried disc is toasted and pounded into the tomato and pork relish nam phrik ong and into the broth of nam ngiao, the noodle soup of the north.
Everything but the last sentence is from the sources cited. The last sentence is kitchen practice: no source read says that nam phrik ong or nam ngiao contains thua nao, and the one study that analyses those two dish names does not mention it.
Storage and freshness
| Form | Good for | Conditions | Fridge |
|---|---|---|---|
| Fresh | 0–0 months | Cold. In one trial, steamed thua nao sealed in bags and kept at 4 °C lasted up to 40 days, in air or under vacuum; the same packs kept at 40 °C had spoiled visibly within five. | Yes |
| Dried whole | 3–4 months | Dry. Makers report that long keeping in damp conditions brings mould, and the survey that records this gives 14 per cent moisture as the most the dried product should hold. | — |
| Powder | Not established | — | — |
Look and smell. Ripe thua nao is greyish brown, slightly slimy and smells of ammonia. A review counts it spoiled when it smells putrid or rancid, or shows mould or a yellow slimy film.
- A putrid or rancid smell in place of the ammonia one
- Mould, or a yellow slimy film on the beans
- A strong dark brown colour, or a swollen pack
- Spoilage of the wet beans within days at room temperature
- Mould on dried discs kept damp or dried in wet weather
- Rancidity as the fat oxidises, faster in air
Quality is not the same as safety
A weaker smell in an old disc is a matter of quality. Mould is not, and neither is what one market survey found by culture in fresh and dried samples, which is set out under safety as findings on those samples.
Forms
These forms differ enough to need separate answers: treating them as interchangeable produces a dish that is wrong.
Fresh, wet beans
The fermented beans as they come from the basket, whole or mashed, sold wrapped in banana leaf. Steamed or roasted before they are eaten.
Steamed or roasted first. The fresh beans are then seasoned with chillies, onions and salt and eaten with sticky rice, or cooked into dishes.
Dried discs (thua nao kab)
Fermented beans ground, pressed into a thin disc some 8 to 10 cm across and dried in the sun. The form that keeps and the one used in cooked dishes. Tai Yai speakers in Taunggyi call it by a name a Thai study writes as โถ่เหน้าแค้บ.
Toasted over a flame or in a dry pan until it darkens and smells nutty, then pounded into chilli pastes or crumbled into soups and curries.
Powder
The dried product ground and sold as a powder, which a 2018 market study notes as a recent addition.
Commonly confused with thua nao
Direct comparisons, each with the difference that actually changes what you cook.
Botany
The soybean. The review of thua nao gives the species as Glycine max; the synonyms are in the handbook account of the plant.
Fabaceae
The handbook uses the older family name, Leguminosae.
The ripe, dry seed. Village makers use ordinary yellow soybeans; one laboratory has made it from black-seeded soybeans to study how it dries.
An erect, bushy annual herb, 0.2–1.5 m tall and brownish or greyish hairy, with leaves of three leaflets and small purple or white pea flowers. The pods are slightly curved, 3–15 cm long, and hold two or three seeds as a rule. The seeds are usually round, and yellow, green, brown, black or mottled.
Commonly confused with
Natto
The sticky fermented soybean of Japan. The papers read set the two side by side and name three differences: natto is inoculated with a pure culture of one bacterium, Bacillus subtilis, where thua nao is left to whatever survives the boiling; natto is made in factories and thua nao in households; and natto is eaten plain where thua nao serves chiefly as a condiment. One study that compared their volatile compounds concluded that no systematic difference between them could be stated.
Pe poke
The fermented soybean of Myanmar. In the north-east of the country, next to Thailand, it is pressed into flat wafers and sun-dried as thua nao is; in the north-west, next to India, it is eaten fresh as a side dish and as fritters. The study that says this treats the two as similar foods and does not call them one.
Kinema and cheonggukjang
Fermented soybeans of India, Nepal and Bhutan, and of Korea, which the papers list beside thua nao as foods of the same kind. A study of the Mae Hong Son products notes that kinema beans are lightly crushed and mixed with a little ash before they ferment, and that the bacteria of cheonggukjang come from rice straw. Neither is held in this catalogue.
The fermented soybean of Chinese cooking. Most douchi is grown over with mould, then salted and aged; thua nao is fermented by bacteria in a few days with no salt and no mould intended. One market study lists Chinese douchi among similar fermented soybeans without saying how it differs.
The fermented locust bean of West Africa. The same alkaline fermentation by Bacillus bacteria, on the seed of a different plant. The review of thua nao names it as a similar product.
How it is grown
The plant, how it is propagated and farmed, what threatens the crop, and where it is produced now. Crop diseases here are plant health, not food safety.
The ripe seed of the soybean, two or three to a pod. Makers surveyed in Mae Hong Son and Chiang Mai in 2004 named the varieties they used, a local one and the bred variety SJ. 5; makers in Chiang Rai used whatever was to hand.
From planting to first harvest: 2–5 months
An annual. Seedlings emerge 5–15 days after sowing, flowering begins from 25 to more than 150 days after sowing according to day length, temperature and cultivar, and the whole cycle from sowing to maturity takes from 65 to more than 150 days. It is a short-day plant, maturing sooner under short days.
How it is propagated
- Seed.
An annual field crop grown from seed.
Normally self-pollinated and completely self-fertile, with less than 1 per cent cross-pollination.
The handbook says the soybean originated as a domesticate in the eastern half of north China around the eleventh century BC, and spread from there to Manchuria, Korea and Japan. That is a handbook’s summary and not an archaeological report.
Where it comes from and how it is made
- Thailand (Chiang Mai, Chiang Rai, Mae Hong Son, Lamphun, Lampang, Phayao, Phrae and Nan) — notable producer. The eight provinces of the upper north where a 2004 survey says it is produced. Samples from six of them were collected for a later study of its bacteria.
- Myanmar (Shan State) — notable producer. Named beside northern Thailand as a place where it is made and eaten. Tai Yai people interviewed in Taunggyi named a dish seasoned with it.
Where the sources place it. None gives a quantity produced for a province or a country.
- Soaking and boiling — The dry beans are washed, in most accounts soaked overnight, and boiled for some hours until they crush between the fingers. Karen and Lawa makers in Mae Hong Son leave out the soaking, and Lawa makers boil the beans in the water left from cooking sticky rice.Why: Boiling softens the bean and kills the bacteria that cannot stand heat, leaving the heat-resistant ones to do the fermenting.
- Fermenting — The drained beans are packed into a bamboo basket lined and covered with banana leaves, or in some places fern leaves or a plastic bag, and left for two to four days. Nothing is added: no salt and no starter.Why: Bacillus bacteria break the protein of the bean down and release ammonia, which makes the beans alkaline.
- Using fresh — The ripe beans are greyish brown, slightly slimy and smell strongly of ammonia. They are steamed or roasted before they are eaten, and keep about two days.
- Mashing, shaping and drying — To keep it, the fermented beans are ground in a mortar or a grinder, rolled into a ball, pressed into a thin flat disc and dried in the sun.Why: The dried disc keeps for months where the wet beans keep for days.
An outline of what makers do, as five papers describe it. The times and vessels differ from place to place: a 2004 survey recorded boiling times of five to eight hours and fermenting times of two to four days across three provinces, and a review gives three to four hours and two to three days. It is a description and not a method.
The season shows in the product. Makers interviewed in 2004 said fermentation takes longer in the cool season than in the dry one, and that in the rains there is too little sun to dry the discs, moulds get in and less is made. One district of Mae Hong Son had built a drying shed for that reason.
Fermentation
Thua nao
Alkaline fermentation · Northern Thailand, Shan State, Myanmar · also thua-nao, tua nao, tuanao, thua nao kab, Thai fermented soybean
Soybeans, water and whatever microbes survive the boiling, and nothing else: it is made without salt. The beans are soaked, boiled and left to ferment. Fresh, wet thua nao keeps for about two days, so it is steamed or roasted, or mashed, pressed into flat discs and dried in the sun, and the dried discs keep for months.
Bacillus leads. In 65 samples from villages in six northern provinces, sequenced for their bacteria, it was on average 67 per cent of the community: 86 per cent in the 35 dried samples and 47 per cent in the 30 wet ones, which were more varied and also carried Lactobacillus, Enterococcus and Globicatella. In five village batches followed by culture, Bacillus subtilis was there from start to finish and a Lactobacillus only on the first day. Nothing is inoculated in the village product. In three laboratory batches left to ferment unaided, Bacillus and its relatives and enteric bacteria of the order Enterobacterales together made up over 99 per cent of what was found; one batch was almost wholly the former, and the other two held both throughout. Moulds were grown from dried samples in four of seven districts surveyed.
The two sequencing studies looked at bacteria only.
The village process is described as two to four days at ambient temperature, which one paper gives as 28 to 34 °C; makers say it takes longer in the cool season. The two laboratory studies of its chemistry held their beans at 37 °C for three days, one with a commercial Bacillus subtilis culture. The beans turn alkaline: a review puts the finished product as high as pH 8, and a naturally fermented laboratory product measured 8.23 to 8.69. Dried and market samples are nearer neutral: 6.92 to 7.23 in discs dried four ways in one laboratory, 6.29 to 6.70 in three samples from Mae Hong Son. Earlier analyses, as one paper quotes them, put the water content at 57 to 65 per cent.
Ammonia and pH rose through the three days in five village batches. In laboratory batches acetate rose sharply in the first day, and the free amino acids leucine, alanine, valine and glutamine rose and stayed up, while citrate fell away. One study, read in abstract, put total volatile compounds at 35 micrograms per kilogram in the cooked beans and 3,500 after 72 hours. Wet village samples held more acetate, propionate, butyrate and isovalerate than dried ones. In dried discs made with a starter culture, 65 volatile compounds were identified, among them 2,5-dimethylpyrazine and trimethylpyrazine. How the discs were dried changed the smell: sun-drying gave more of the green, fatty products of fat oxidation such as hexanal, and sun and hot-air drying more of the roasted and smoky compounds of browning than microwave or vacuum drying.
Thai food scientists describe it as serving chiefly as a condiment, or mixed into chilli pastes, and not eaten plain as Japanese natto is. Another group describes a savoury taste and a strong meaty smell, and notes that it is free of salt, unlike shrimp paste. A Thai study of dish names calls it the main seasoning of Tai Yai cooking. Across the border in north-eastern Myanmar, pe poke is pressed into wafers and sun-dried in the same way; in Myanmar the fresh beans are also eaten as a side dish and as fritters.
One survey cultured 24 market samples from Chiang Rai and Phayao, nine fresh and fifteen dried. Escherichia coli was grown from 13, Salmonella from three and Bacillus cereus from two; Clostridium perfringens and Staphylococcus aureus from none. A survey of dried thua nao from seven districts grew Aspergillus flavus and Aspergillus niger from the samples of two, and measured no toxin. The authors of the village-batch study note that the product is cooked again, by steaming or roasting, before it is eaten.
Presence or absence by culture in those samples. No measurement of a toxin or of biogenic amines in thua nao was read.
What goes into it
- Fermented: Soybeans (Soaked and boiled, with no salt and nothing inoculated in the village product. The bean itself has no page here; the fermented product does.); Black soybeans (In one laboratory study of drying only. Village makers surveyed used ordinary soybean varieties.)
- Starter or culture: Commercial Bacillus subtilis culture (In the same laboratory study only. The village product has no starter.)
Organisms studies found, and how
- Lactic acid bacteria: Lactobacillus sp. — detected, grown in culture. The same five Chiang Rai batches: present at the onset, from 12 to 24 hours, and not later. Sources: Microbiological and Biochemical Changes in… (Results and Discussion) Lactobacillus, Enterococcus and Globicatella — detected, found by sequencing. Enriched in the 30 wet samples against the 35 dried ones in the survey of six provinces. Sources: Microbiome analysis of thai traditional fer… (Results, Bacterial taxonomic signatures of Thua Nao) Leuconostocaceae — detected, grown in culture and found by sequencing. Thua nao from one sub-district of Mae Hong Son followed for two days: found beside the Bacillus that made up most of the community. Sources: Bacterial compositions of indigenous Lanna… (Results; Discussion)
- Bacillus and its relatives: Bacillus — reported as dominant, found by sequencing. Sixty-five samples from villages in six northern Thai provinces: on average 67 per cent of the bacteria, 86 in dried samples and 47 in wet ones. Sources: Microbiome analysis of thai traditional fer… (Abstract; Results, Bacterial taxonomic signatures of Thua Nao) Bacillus — reported as dominant, found by sequencing. Samples of Shan thua nao from one market in Mae Hong Son: 82.7 to 86.8 per cent of the bacteria. Karen and Lawa products held 76.9 to 83.6 and 49.0 to 60.6. Sources: Bacterial Communities in Lanna Fermented So… (Section 3.2) Bacillus subtilis — reported as dominant, grown in culture. Five batches made by a village group in Chiang Rai and sampled every twelve hours: predominant through all 72 hours, with Bacillus pumilus also grown. Sources: Microbiological and Biochemical Changes in… (Results and Discussion) Bacillus subtilis — added as a starter, added by the maker. Black soybean thua nao made in one laboratory to compare ways of drying it. Sources: Impact of drying techniques on volatile aro… (Section 2.1)
- Other bacteria: Vagococcus and Proteus — detected, found by sequencing. The Shan samples from one Mae Hong Son market only: 3.7 to 5.3 and 2.8 to 5.0 per cent. The authors read Proteus as a sign that hygiene needs watching. Sources: Bacterial Communities in Lanna Fermented So… (Section 3.2; Discussion) Enterobacterales — detected, found by sequencing. Three laboratory batches left to ferment unaided; present throughout in two of them. Sources: Insights into Microbial and Metabolite Prof… (Results, section 3.2.1) Escherichia coli — detected, grown in culture. Grown from 13 of 24 market samples, fresh and dried, in Chiang Rai and Phayao. Salmonella was grown from three and Bacillus cereus from two. Sources: Microbiological quality of commercial Thua… (Results and Discussion; Table 2)
- Moulds: Rhizopus spp. — detected, grown in culture. Dried thua nao from three of seven districts surveyed in 2004. Aspergillus flavus and A. niger were grown from two. Sources: A Study on Production Processes and Quality… (Table 3)
What was measured to change
Each of these was measured before and after, or at several points on the way, in the study named. It is a finding about that study’s material.
Measured to rise during the process
- Ammonia. The text says pH, ammonia and total protein increased as the fermentation proceeded. The figures are in a table that could not be read, so none is given. Compared: Samples taken every twelve hours from 0 to 72 hours. Several samples: Five batches made in the usual way by a village women’s group in Chiang Rai in late 2004. The authors’ own explanation: The authors put the rise in pH down to the breakdown of protein and the release of ammonia as the microbes use the amino acids. Sources: Microbiological and Biochemical Changes in… (Results and Discussion)
- Total volatile compounds. From 35 to 3,500 micrograms per kilogram wet weight. Sun-drying the 72-hour material then lost 65 per cent of the total, and two commercial dried samples held 380. Compared: Cooked soybeans against the same material after 72 hours. A laboratory batch: Soybeans fermented by their natural flora in one laboratory; the number of batches is not in the abstract. Sources: Volatile compounds in Bacillus-fermented so… (Abstract)
- Free amino acids. The abstract says both fermented products had much higher concentrations than their unfermented counterparts, and the starter-made one more than the other. It gives no figure. Compared: Cooked, unfermented soybeans against two finished thua nao. A laboratory batch: One thua nao made with a single Bacillus subtilis strain and one fermented unaided, in one laboratory. Sources: Free-amino acid profiles of thua nao, a Tha… (Abstract)
- Leucine, alanine, valine and glutamine. Small shares of the NMR profile at day 0, larger after 24 hours and remaining so, along with succinate. Shares of a profile, not concentrations. Compared: Day 0 against days 1, 2 and 3. A laboratory batch: Three laboratory batches from different lots of soybean, fermented unaided for three days. Sources: Insights into Microbial and Metabolite Prof… (Results, section 3.2.2; Figure 2a)
Measured to fall during the process
- Citric acid. Citrate was among the largest shares of the NMR profile at day 0, fell dramatically within 24 hours and stayed low to day 3. Shares of a profile, not concentrations. Compared: Day 0 against days 1, 2 and 3. A laboratory batch: Three laboratory batches from different lots of soybean, fermented unaided for three days. Sources: Insights into Microbial and Metabolite Prof… (Results, section 3.2.2; Figure 2a)
Measured to rise and then fall during the process
- Acetate. Its share of the metabolites seen by NMR rose sharply in the first 24 hours and then declined gradually. Shares of a profile, not concentrations. Compared: Day 0 against days 1, 2 and 3. A laboratory batch: Three laboratory batches from different lots of soybean, fermented unaided for three days. Sources: Insights into Microbial and Metabolite Prof… (Results, section 3.2.2; Figure 2a)
Found in the finished product
These were measured in the finished product only. That shows they are there; it does not show that the process made them.
- 2,5-Dimethylpyrazine. The most abundant pyrazine: 11,097 micrograms per kilogram in sun-dried discs, 8,143 hot-air-dried, 6,604 microwave-vacuum-dried and 3,568 vacuum-dried, as relative concentrations. Analysed: Finished dried discs, dried four ways. That study measured nothing before or during the fermentation. A laboratory batch: Dried discs of black soybean thua nao made in one laboratory with a starter culture. Sources: Impact of drying techniques on volatile aro… (Table 3; section 3.4.2)
- Guaiacol. Listed as 2-methoxy-phenol, with a smoky, woody odour: 3,897 micrograms per kilogram in sun-dried discs, 3,593 hot-air-dried, 1,478 microwave-vacuum-dried and 901 vacuum-dried. Analysed: Finished dried discs, dried four ways. That study measured nothing before or during the fermentation. A laboratory batch: Dried discs of black soybean thua nao made in one laboratory with a starter culture. Sources: Impact of drying techniques on volatile aro… (Table 3; section 3.4.2)
- 2-Methylbutanoic acid. The most abundant branched volatile acid, at 37,090 to 51,842 micrograms per kilogram across the four ways of drying, as relative concentrations. Analysed: Finished dried discs, dried four ways. That study measured nothing before or during the fermentation. A laboratory batch: Dried discs of black soybean thua nao made in one laboratory with a starter culture. Sources: Impact of drying techniques on volatile aro… (Table 3; section 3.4.3)
- Acetate, propionate, butyrate and isovalerate. Each of the four was higher in the wet samples than in the dried, and acetate was the most abundant in both. The figures are in a chart and are not given in the text. Analysed: Thirty wet samples against 35 dried ones, as collected; not the same batches before and after drying. Several samples: Sixty-five village samples from six northern Thai provinces, measured by gas chromatography. Sources: Microbiome analysis of thai traditional fer… (Results, Natural SCFA levels of Thua Nao)
What is not established: Most of the flavour chemistry comes from laboratory batches, one of them inoculated and made from black soybeans, and three papers on its volatiles and amino acids were read in abstract only. The village study that followed ammonia through the fermentation gives its figures in a table that could not be read. No measurement of a toxin or of biogenic amines in thua nao was read. Pe poke, its relative across the border, is described in the one paper read on it as a side dish and as fritters as well as sun-dried wafers, and is not recorded as a seasoning.
Buying and quality
- Sold fresh in banana leaf, as thin dried discs, or as powder.
- Fresh beans greyish brown and slightly slimy, with a clean smell of ammonia and nothing putrid or rancid.
- Dried discs dry and free of mould; makers name the rainy season as the time when drying fails.
Safety
Safety statements on SpiceHQ must cite evidence — they cannot be published on editorial judgement.
Soy is a declared allergen
Applies to: Anyone with a soy allergy, and anyone cooking for them
Thua nao is fermented soybean. Soybeans and products made from them must be declared on food labels in the EU and Northern Ireland, and soybeans are one of the major food allergens requiring declaration in the United States.
What one survey found in market samples
Applies to: A description of the samples studied, not guidance
In 24 samples bought in markets in Chiang Rai and Phayao, nine fresh and fifteen dried, Escherichia coli was grown from 13, Salmonella from three and Bacillus cereus from two, both of those dried. Clostridium perfringens and Staphylococcus aureus were found in none. Total bacteria ran from 5.53 to 7.97 log units per gram and moulds from 4.00 to 7.29. A separate survey of dried thua nao from seven districts grew Aspergillus flavus and Aspergillus niger from the samples of two; it measured no toxin.
Findings on those samples, by culture, with no counts for the bacteria tested for. The authors of the first call their data preliminary. A 2024 survey of biogenic amines in commercial thua nao exists and could not be read, so nothing is said about amines.
- Soybeans — a declarable allergen in the EU and US
Soybeans must be declared in both the EU and the United States. This is a statement about labelling law rather than about whether allergy occurs — allergic reactions to spices are documented and are not a labelling category — and it is the part of the answer that differs by where the food is sold.
History and trade
No dated history of thua nao was read, and the papers that mention its past only assert it. One says it has been made in northern Thailand and the Shan State of Myanmar for centuries, another that it originated in northern Thailand; neither cites evidence. What the sources do establish is whose food it is now. A study of the fermented soybeans of Mae Hong Son says thua nao is the Shan name, which Thai has taken for the products of every group. The authors of a study of pe poke say there is no historical record of where that food began, and report a belief that the soybean reached Myanmar from Yunnan.
Statements in the introductions of food-science papers. No historical or ethnographic work on its origins was read, and the earliest study the papers cite, from 1972, was not seen.
Claims we do not accept at face value
“Thua nao is Thai natto.”
popular but unsupported
The papers call the two similar and then separate them: natto is made in factories with one chosen bacterium and eaten plain, thua nao in households with whatever survives the boiling and used mostly as a seasoning. Nothing read says one came from the other.
“Thua nao has been made for centuries.”
popular but unsupported
It may well have been. The statement appears in the introduction of a food-science paper without a source, and no dated evidence was read.
Culture
Recorded by tradition rather than merged into one narrative — these are genuinely different practices.
Shan (Tai Yai)
Among the Shan (Tai Yai) of Shan State and Mae Hong Son (Myanmar and Thailand). Shared by northern Thailand and the Shan State of Myanmar.
The seasoning of Tai Yai cooking. A Thai study of dish names, citing an earlier Thai work, calls the use of thua nao as the main seasoning the mark of Tai Yai food, and concludes that where Lanna cooking seasons with fermented fish, crab paste or the liquor of fermented tea, Tai Yai cooking mostly uses this bean. Tai Yai people interviewed in Taunggyi named a dish of mushrooms simmered with it. The same study gives two forms by their Tai Yai names: the steamed whole beans, and the ground beans made into round sheets and sun-dried.
- Mushrooms simmered with thua nao, a Tai Yai dish recorded in Taunggyi
- Steamed whole beans and sun-dried round sheets as the two forms
Karen and Lawa villages of Mae Hong Son
Among the Karen and Lawa of Mae Hong Son, Thailand.
Both groups make a fermented soybean of their own and call it by their own name, Tor-Nor-Au and Kuem. Neither soaks the beans first. Lawa makers boil them in the water kept from cooking sticky rice and keep the batch beside the stove; Karen makers sun-dry theirs. Bacillus was the main bacterium in all three, at 49 to 61 per cent of the Lawa samples and 77 to 87 per cent of the Karen and Shan ones.
Six samples in all, from one village or market for each group.
- Beans boiled in sticky-rice water (Lawa)
- No soaking before boiling
Northern Thailand (Lanna)
Made in households across the upper north and sold in village, district and provincial markets as dried, spiced and grilled or fried thua nao. Thai food scientists describe it as a condiment and a cheap source of protein: the fresh beans are seasoned and eaten with sticky rice, and the dried discs go into many local dishes, which the papers do not name. A dish named ถั่วเน่าเมอะ is among the Lanna dish names a Thai study took from the Chiang Mai University library’s pages on Lanna food.
The dish name is given in Thai letters as the study prints it, without a romanisation or a translation, because the study gives neither and does not describe the dish.
- Fresh thua nao seasoned and eaten with sticky rice
- Dried discs used in cooked dishes
Also documented in northern Thailand: Cha phlu, Litsea berry, Makwaen, Vietnamese coriander.
Myanmar
Pe poke, the fermented soybean of northern Myanmar, is described by those who study it as similar to thua nao. In the north-east, next to Thailand, the fresh beans are mashed, sometimes with salt and hot pepper, shaped into flat wafers and sun-dried. In the north-west, next to India, they are eaten fresh as a side dish and as fritters. The same authors say it is sold in local markets by small farmers and that younger people eat less of it.
Four samples from one village in Mandalay were studied; the account of how it is eaten is the authors’ own.
- Sun-dried wafers of mashed pe poke
What it is called
- Thai: ถั่วเน่า (thua nao)
- Thai: thua nao kab
- Shan (Tai Yai), in Thai letters: โถ่เหน้าแค้บ
- Shan (Tai Yai), in Thai letters: โถ่เหน้าเม็ด
- As used in Myanmar: pe poke
What we do not know
Published openly. A gap we have named is more useful than a gap we have filled with plausible prose.
Not yet established for thua nao:
- Historical timeline
- Ceremonial use
- Traditional medicinal context
- Traditional uses