Thai script แกงส้ม. TCPS 855/2563 defines the wet product as chilli, onion, fingerroot and turmeric, with shrimp paste and salt, plus fish or shrimp, soured with tamarind and lime and seasoned with fish sauce and sugar — no coconut milk anywhere, and a pH capped at 4.6. Its labelling clause lets the same product be sold as น้ำแกงเหลือง, gaeng leuang. The older TCPS 733/2548 covers the dried version and names fingerroot too, but not turmeric. Three of the four current certificate holders are in the south. Contains shrimp and fish, and the label must say so.
What the Thai government says gaeng som is
The Thai Industrial Standards Institute publishes the Thai Community Product Standard series through the Ministry of Industry. Searching its register for แกงส้ม returns two documents. The current and more detailed one is TCPS 855/2563, น้ำแกงส้ม, whose English title in the standard itself is Sour and Spicy Soup — issued as TISI notification No. 2339 of 3 July 2563, signed by Secretary-General Wanchai Phanomchai, cancelling the 2548 version that had stood since April of that year.
| Ingredient | Thai | How the standard treats it |
|---|---|---|
| Chilli | พริก | Spice and herb group - washed clean, then pounded or ground together |
| Onion or shallot | หัวหอม | Spice and herb group |
| Fingerroot | กระชาย | Spice and herb group - the marker of this curry, and it is in both standards |
| Turmeric | ขมิ้น | Spice and herb group - named here but not in the 2548 dried standard |
| Shrimp paste | กะปิ | Optional addition - the reason the label carries a shellfish allergen line |
| Salt | เกลือ | Optional addition |
| Fish or shrimp | ปลา / กุ้ง | Boiled, then finely ground or left in pieces |
| Tamarind water | น้ำมะขามเปียก | Seasoning group - the sourness the name refers to |
| Lime juice | น้ำมะนาว | Seasoning group |
| Fish sauce | น้ำปลา | Seasoning group |
| Sugar | น้ำตาล | Seasoning group |
The absence is as informative as the list. There is no coconut milk in the definition, and no galangal, no lemongrass, no kaffir lime leaf — the aromatics that carry most Thai curries. What is there instead is fingerroot, and a sourness that comes from tamarind and lime rather than from anything fermented. That is why gaeng som reads as thin, sharp and slightly bitter beside a green curry, and why people who order it expecting tom yum are surprised.
Two standards, and the one difference between them
| Standard name | Number | What it covers |
|---|---|---|
| น้ำแกงส้ม - sour and spicy soup | 855/2563 | The wet product, hot-filled and retorted. pH capped at 4.6. Turmeric and fingerroot both named. Four current certificate holders. |
| แกงส้มกึ่งสำเร็จรูป - semi-cooked sour spicy soup | 733/2548 | The dried, ready-to-cook powder. Moisture capped at 12 per cent, water activity at 0.6, aflatoxin at 20 micrograms per kilogram. No current certificate holder. |
Read the two definition clauses side by side and one ingredient moves. Fingerroot is in both. Turmeric is in the 2563 wet standard and not in the 2548 dried one, whose paste is dried chilli, shallot, shrimp paste and fingerroot. We are not going to turn that into a regional theory, because neither document names a region and fifteen years separate them. What we can say is that the more recent standard, the one with turmeric in it, is also the one whose labelling clause admits the name gaeng leuang — yellow curry — and turmeric is what makes a curry yellow.
Gaeng leuang is a permitted label for the same product
Clause 6.1(1) of TCPS 855/2563 requires the container to show the product name from the standard, or a name conveying the same meaning, and gives two examples of what that may look like: น้ำแกงส้มกึ่งสำเร็จรูป, semi-instant gaeng som liquid, and น้ำแกงเหลือง พร้อมปรุง, ready-to-cook gaeng leuang liquid. In the Ministry of Industry’s own filing, a certified gaeng som producer may put gaeng leuang on the jar.
That is a real finding and it is also a limited one. A labelling clause governs what a packaged product may be called; it does not tell you that a cook in Trang and a cook in Ayutthaya make the same thing. What it does do is remove the strongest possible source for the claim that these are two separate curries: the government had an opportunity to separate them and did the opposite.
Where the certificates actually sit
We queried the certificate register directly on 8 September 2026. TCPS 855/2563 has four current holders, and three of them are in the south: a producer group in Sadao district, Songkhla; an individual producer in Mueang Chumphon district, Chumphon, certified for a mild ready-cooked version; and a community enterprise in Pa Bon district, Phatthalung whose registered name is a curry-paste enterprise. The fourth is a limited partnership in Tha Muang district, Kanchanaburi. The older dried standard, TCPS 733/2548, has no current holder at all.
Four certificates is a small sample and we will not dress it up as more. But three of four in Songkhla, Chumphon and Phatthalung is a southern concentration in the government’s own data, and it is worth more than the same claim asserted without evidence. Certificates are issued by the province’s industry office and expire after three to five years; we name districts and provinces rather than people, because many holders are private individuals whose addresses and mobile numbers are published in the register.
What we could not confirm, and did not invent
- The vegetables. Neither standard names one. Not the cha-om omelette, not the papaya, not the cabbage, not the daikon, not the pineapple. Everything you see in a bowl beyond the fish is outside both documents.
- Proportions. No quantity of anything appears in either definition clause, so there is no official ratio, no official chilli count and no official sourness.
- The central versus southern split. Widely described, and consistent with where the certificates sit, but neither standard names a region and we treat it as an inference from the register rather than a stated fact.
- A separate curry paste standard. TCPS 855/2563 refers to a ready-made gaeng som curry paste, but the register returns no published standard under that name, so we make no claim about what such a paste must contain.
- Any heritage listing. The Department of Cultural Promotion’s intangible cultural heritage portal at ich.culture.go.th does not resolve, so we make no claim in either direction.
- Prices, and where to eat it. No official source for either, and we do not name restaurants we cannot verify.
Frequently asked questions
Thailand defines it twice, for two different products. TCPS 855/2563, the standard for the wet sour and spicy soup, defines it as spices and herbs such as chilli, onion, fingerroot and turmeric, washed clean, with other ingredients such as shrimp paste and salt optionally added, pounded or ground together - or a ready-made gaeng som curry paste dissolved in water - then meat such as fish or shrimp, boiled and either finely ground or left in pieces, seasoned with tamarind water, lime juice, fish sauce and sugar, boiled, filled hot, reheated in its container and cooled immediately. The older TCPS 733/2548 covers the dried, ready-to-cook version and names dried chilli, shallot, shrimp paste and fingerroot in its paste, with cooked fish or shrimp, tamarind water and fish sauce. Fingerroot - กระชาย - appears in both, and it is the ingredient that distinguishes this curry from the rest of the Thai repertoire. Neither standard gives quantities, so nobody can tell you the ratio from an official source, and neither names a vegetable.
In the Ministry of Industry's own labelling rule, they are the same class of product. TCPS 855/2563 clause 6.1(1) tells a producer to use the standard's product name or a name conveying the same meaning, and gives two worked examples: น้ำแกงส้มกึ่งสำเร็จรูป, semi-instant gaeng som liquid, and น้ำแกงเหลือง พร้อมปรุง, ready-to-cook gaeng leuang liquid. So a producer certified against the gaeng som standard may sell the product as gaeng leuang. That is not the same as saying the two dishes are identical on a table in Trang and a table in Ayutthaya - the standard settles what may go on a label, not what a cook does. But it does mean the widely repeated claim that gaeng leuang is a separate curry has no support in the one document that had an opportunity to separate them.
Two reasons, and both are in the definitions. First, fingerroot. กระชาย is named in the definition clause of both standards and appears in neither the khao soi paste standard nor the northern sausage standard nor the larb spice standard - it is specific to this curry family. Second, there is no coconut milk anywhere in either definition. The liquid is water, soured with tamarind and lime and salted with fish sauce and shrimp paste, at a pH the standard caps at 4.6. A curry that is thin, sharp and has no dairy or coconut fat to round it off is going to read very differently from a massaman or a green curry, and that difference is written into the specification rather than being a matter of style.
Assume yes. Shrimp paste - กะปิ - is named in the definition clause of both standards, and TCPS 855/2563 clause 6.1(7) requires the container to carry the allergen line ข้อมูลสำหรับผู้แพ้อาหาร : มีกุ้งและปลา, information for food allergy sufferers: contains shrimp and fish, where shrimp and fish are ingredients. The definition also puts fish or shrimp meat in the soup itself. If you have a shellfish allergy, that line is the one to look for on a jar, and a restaurant is not bound by the standard at all - so ask, and expect the answer to be yes.
This is the one question where the register gives an unusually clean answer. On 8 September 2026 the certificate register returned four current holders of TCPS 855/2563, and three of the four are southern: a producer group in Sadao district, Songkhla; an individual producer in Mueang Chumphon district, Chumphon, certified for a mild version; and a community enterprise in Pa Bon district, Phatthalung, whose registered name is a curry-paste enterprise. The fourth is a limited partnership in Tha Muang district, Kanchanaburi. That is a southern cluster in the government's own data, and it is consistent with the dish's reputation - but it is four certificates, which is a small number, and the register counts certificates rather than cooks. The older dried standard, TCPS 733/2548, has no current holder at all. We name districts and provinces rather than people, because holders are often private individuals whose addresses are published.
Souring and heat, mostly. TCPS 855/2563 caps pH at 4.6, which is the threshold below which Clostridium botulinum does not grow - and the standard pairs it with a process description that requires the soup to be filled hot, reheated with the container sealed, and cooled immediately. Its microbiological ceilings follow from that: Salmonella must not be detected in a 25 gram sample, Staphylococcus aureus must be under 10 colonies per gram, Bacillus cereus and Clostridium perfringens are each capped at 1,000 per gram, E. coli must be under 3 per gram by the MPN method, and yeast and mould at 100 per gram. The dried standard manages a different risk: moisture no higher than 12 per cent by weight, water activity no higher than 0.6, and aflatoxin no higher than 20 micrograms per kilogram, which is the dried-chilli risk being controlled. Neither set of numbers applies to a bowl cooked to order.
Related guides
- Khao soi — the northern noodle bowl, and the curry powder written into its standard.
- Som tam — the dressing standard, and the pla ra clause that sets zero tolerance for liver fluke larvae.
- Thai regional food — how the four regional kitchens actually differ.
- Dining in Hat Yai — eating in the southern city most foreigners pass through first.
- Living in Songkhla — the province holding one of the four certificates.
- Cost of living in Nakhon Si Thammarat — what the deep south costs to live in.
- Living in Surat Thani — the gateway province for the Gulf islands.
- Thai street food — how ordering actually works.
The south is where this curry is certified, and where the property is cheapest per square metre
If southern food is what put Songkhla or Nakhon Si Thammarat on your list, start with what a month there costs.
Sources & References
- Thai Industrial Standards Institute, Ministry of Industry - Thai Community Product Standard TCPS 855/2563, Sour and Spicy Soup (Nam Gaeng Som), ICS 67.040, ISBN 978-616-475-644-1. Its definition clause 2.1 names spices and herbs such as chilli, onion, fingerroot and turmeric, washed clean, with other ingredients such as shrimp paste and salt optionally added, pounded or ground together - or a ready-made gaeng som curry paste dissolved in water - with meat such as fish or shrimp, boiled and finely ground or in pieces, seasoned with tamarind water, lime juice, fish sauce and sugar, boiled, hot-filled, then reheated with the container and cooled immediately. Clause 3.6 caps pH at 4.6. Clause 6.1(1) permits the product to be labelled with a name conveying the standard's meaning, giving semi-instant gaeng som liquid and ready-to-cook gaeng leuang liquid as examples. Clause 6.1(7) requires the allergen line for shrimp and fish. Issued as TISI notification No. 2339 (B.E. 2563) of 3 July 2563, signed by Secretary-General Wanchai Phanomchai, cancelling TCPS 855/2548
- Thai Industrial Standards Institute - Thai Community Product Standard TCPS 733/2548, Semi-Cooked Sour Spicy Soup. Its definition clause 2.1 names herbs and spices such as dried chilli, shallot, shrimp paste and fingerroot, washed clean and ground together into a curry paste, with cooked fish or shrimp meat added, seasoned with tamarind water and fish sauce, mixed, oven-dried and ground again. It caps moisture at 12 per cent by weight, water activity at 0.6 and aflatoxin at 20 micrograms per kilogram, and permits the label to read semi-instant gaeng som, oven-dried gaeng som or ready-to-cook gaeng som. Turmeric is not named in this standard's definition clause
- Thai Industrial Standards Institute - the public register of published community product standards, queried directly on 8 September 2026. Searching gaeng som returns exactly two standards: 733/2548 semi-cooked sour spicy soup and 855/2563 sour and spicy soup. There is no separate published standard for a gaeng som curry paste under that name, although the 855/2563 definition clause refers to one
- Thai Industrial Standards Institute - the public register of certified community producers, queried directly on 8 September 2026. Against TCPS 855/2563 it returns four current certificate holders: a producer group in Sadao district, Songkhla; an individual producer in Mueang Chumphon district, Chumphon, certified for a mild ready-cooked gaeng som liquid; a community enterprise in Pa Bon district, Phatthalung whose registered name is a curry-paste enterprise; and a limited partnership in Tha Muang district, Kanchanaburi. Against TCPS 733/2548 it returns no current certificate holder
Primary and official sources are cited above. Government rules, fees and procedures in Thailand change over time and vary by office; always confirm current requirements with the relevant authority before relying on them. BAANLYY never takes paid placement in editorial content.
