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Fish and seafood from Thailand

Hoi-somหอยส้ม

Hoi-som is shelled venus clam meat salted 3 to 1 by weight, mixed with rice-washing water and a little sugar and left to ferment for 3 days. The starch and sugar feed lactic acid bacteria, so the white meat turns sour as well as salty.

Fully documentedFish and seafood3 days

Recipe

Amounts from a sourceMeat-to-salt ratio of 3:1 by weight from the JIRCAS database of Thai fermented foods (after The Traditional Fermented Foods of Thailand, 1995). The rice water and sugar have no fixed amounts.
Venus clam meat3 parts by weightTaken out of the shell and washed[jircas-hoisom]
Salt1 part by weight[jircas-hoisom]
Nam-sao-khao (water from washing rice)Some[jircas-hoisom]
SugarA small amount[jircas-hoisom]

Total time across the recorded steps: 3 days

Start
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What changes: Starting material: venus clam meat taken out of the shell and washed

Step 1 of 5
Shuck and wash the clam meat
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Which microbes the steps name, step by step
Pediococcus halophilus
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

At a glance

Hoi-som is shelled venus clam meat salted 3 to 1 by weight, mixed with rice-washing water and a little sugar and left to ferment for 3 days. The starch and sugar feed lactic acid bacteria, so the white meat turns sour as well as salty. Made in 5 steps over 3 days. The longest step, ferment, takes 3 days (JIRCAS 1995). Salt is 25 % (JIRCAS 1995). Pediococcus halophilus does most of the fermenting.

Key numbers
Main step3 daysReported[jircas-hoisom]Ferment
Salt25 %Reported[jircas-hoisom]Mix with salt

What makes this one different

Hoi-som is the only one of the Thai shellfish ferments that adds rice-washing water and sugar, so it sours like plaa-som. Hoi-kraeng-dorng and hoi-siap-dorng are cured whole in fish sauce instead.

Related ferments

Safety

The Thai community product standard for pickled shellfish (หอยดอง) covers shellfish pickled with seasonings, giving salt, brine, fish sauce, white soy sauce and vinegar as examples. It does not name hoi-som, which is soured in rice-washing water. For the pickled shellfish it covers, the standard requires no Salmonella in 25 g, no Staphylococcus aureus in 0.1 g, no Clostridium perfringens in 0.01 g, E. coli below 3 MPN per gram and no more than 100 mould colonies per gram, and bans preservatives and synthetic colours. The method has no cooking step. In a survey of 335 fresh fish and shellfish samples from Bangkok markets, 59 % carried Vibrio parahaemolyticus, with the highest share (78 %) in blood cockle. The survey sampled shrimp, oysters, blood cockles and seabass, not venus clams or hoi-som. The authors name V. parahaemolyticus and Salmonella as leading causes of foodborne diarrhoea in Thailand.

History and sources

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

History
The sources we found do not record its history.
Starter
The sources we found do not say how its fermentation begins.
  1. [jircas-hoisom] JIRCAS, Database of Fermented Foods of Thailand: Hoi-som (after The Traditional Fermented Foods of Thailand, 1995)gov
  2. [tcps320] Thai Industrial Standards Institute, Thai Community Product Standard มผช.320/2547, Pickled shellfish (หอยดอง) (copy on archive.org)spec
  3. [suwannaphan2021] Suwannaphan S. 2021, Isolation, identification and potential probiotic characterization of lactic acid bacteria from Thai traditional fermented food, AIMS Microbiol. 7(4):431–446paper
  4. [atwill2021] Atwill, Jeamsripong and LaMontagne, 2021, Bacterial diversity and potential risk factors associated with Salmonella contamination of seafood products sold in retail markets in Bangkok, Thailand, PeerJ 9:e12694paper