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Fermentation Atlas

Fish and seafood from Thailand

Plaa-somปลาส้ม

Sour fish fried before eating; pH 4.3-5.3, protein 16-19%; keeps about 3 weeks (JIRCAS). Made in 4 steps over 5 days – 7 days. The longest step, ferment wrapped or in jars, takes 5–7 days (JIRCAS 1995) and runs at 30 °C. Salt is 2–11.1 % (JIRCAS 1995). Pediococcus pentosaceus and Lactobacillus alimentarius/farciminis do most of the fermenting.

Key numbers
Main step5–7 daysReported[jircas-plaasom]Ferment wrapped or in jars
Temperature30 °CTypicalFerment wrapped or in jars
Salt2–11.1 %Reported[jircas-plaasom][s1]Salt
AciditypH 6 → 4.5Measured[s1]Ferment wrapped or in jars
DocumentedFish and seafood5 days – 7 daysMore fish and seafoodMore from ThailandMore from Laos

Recipe

No fixed amounts recordedWhat goes in. No source gives amounts for this ferment.
freshwater fish: snakehead or barbs (Probarbus jullieni, Puntius gonionotus), Pangasius, Labiobarbus, Cirrhinus microlepis
salt
cooked rice or roasted rice
garlic, or palm syrup
Starter: spontaneous

Total time across the recorded steps: 5 days – 7 days

Start
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What changes: Starting material: cleaned freshwater fish, whole or filleted

Step 1 of 4
Clean fish, whole or fillets
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Which microbes the steps name, step by step
Lactic acid bacteria
Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

Not documented for this step.

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

Variants

  • Plaa-som fak (som fak)minced or scraped fish pounded with rice, garlic and salt, wrapped in banana leaf; a fish "sausage" (see som-fak).
  • Koong-somShrimp made the same way; it turns pink (JIRCAS).

Safety

eaten fried; raw freshwater cyprinids carry liver fluke risk if undercooked (typical).

History and sources

Every number is labelled with how it is known. How this atlas is made

  1. [s1] Paludan-Müller C. et al., Fermentation and microflora of plaa-som, a Thai fermented fish product, Int. J. Food Microbiol. 2002, https://orbit.dtu.dk/en/publications/fermentation-and-microflora-of-plaa-som-a-thai-fermented-fish-pro/paper
  2. [s2] Narzary et al. 2021paper
  3. [jircas-plaasom] JIRCAS, Database of Fermented Foods of Thailand: Plaa-som / Koong-som (after The Traditional Fermented Foods of Thailand, 1995)gov