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Whole skate is laid in a straw-lined jar with no salt and left for about ten days to a month. Bacteria break down the urea in the skate's flesh into ammonia, so the fish turns alkaline and takes on a sharp ammonia sting instead of going sour. It is eaten raw, often as samhap with pork and kimchi.
Fully documentedFish and seafood10 days – 30 days
Recipe
No fixed amounts recordedTraditional process with no fixed batch size. Only skate goes into the jar, so the fish is the whole recipe.
Skate, whole or in pieces
Like sharks and rays, skate holds urea and TMAO in its flesh[shinan][piao2022]
Studies ferment the flesh with no salt or other additives[piao2022]
Total time across the recorded steps: 10 days – 30 days
Start
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What changes:Starting material: whole skate, with no salt added
Step 1 of 4
Take the skate from the catch
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Heuksando skate was carried for days to Naju, and it ripened on the way. Output: whole skate, unsalted.
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
Whole skate is laid in a straw-lined jar with no salt and left for about ten days to a month. Bacteria break down the urea in the skate's flesh into ammonia, so the fish turns alkaline and takes on a sharp ammonia sting instead of going sour. It is eaten raw, often as samhap with pork and kimchi. Made in 4 steps over 10 days – 30 days. The longest step, ripen until the ammonia sting develops, takes 10–30 days (Shinan County Office) and runs at 4–20 °C (Choi M.R 2003). Psychrobacter, Pseudomonas and Oblitimonas and Pseudomonadales, Alteromonadales and Burkholderiales do most of the fermenting.
Most fish ferments are salted and go sour. Hongeo gets no salt at all and goes alkaline, because its own urea turns into ammonia. That makes it a close cousin of Icelandic hákarl and kæst skata rather than of Korean jeotgal.
Hongeo samhapRipened skate eaten with steamed pork (bossam) and kimchi, the "three together".
Safety
Hongeo has no salt and no acid to protect it; its pH climbs instead (8.9 by day 4 at 20 °C in one study). The FDA's pathogen table puts the top pH for growth of Clostridium botulinum at 9 and of Staphylococcus aureus at 10, so the alkali alone is not a full barrier. Clostridium was among the abundant genera in all samples from five commercial plants in one study, whose abstract names no species and reports no toxin test. Ripening cold slows the change; at 4 °C the pH and ammonia hardly rose. The same FDA table has C. botulinum type E growing from 3.3 °C, so cold is no guarantee either. We found no study showing this process is safe. Do not copy it at home, because unsalted raw fish in a closed jar is a botulism risk.
Hazards the sources name: Clostridium (genus abundant in all samples from five commercial plants; the abstract names no species and reports no toxin test).
Skate caught off Heuksando was carried for days to Naju and ripened on the way, which is the origin story told by Shinan county. Jeong Yak-jeon's fish guide Jasan-eobo (1814) notes that people near Naju liked to eat it.
Starter
The sources we found do not say how its fermentation begins.
[zhao2020] Zhao C.C. and Eun J.B. 2020, Shotgun metagenomics approach reveals the bacterial community and metabolic pathways in commercial hongeo product, a traditional Korean fermented skate product, Food Res. Int. 131:109030, doi:10.1016/j.foodres.2020.109030 (abstract)paper
[zhao2019] Zhao C.C., Kim D.W., Eun J.B. 2019, Physicochemical properties and bacterial community dynamics of hongeo, a Korean traditional fermented skate product, during fermentation at 10 °C, LWT 104:109–119, doi:10.1016/j.lwt.2019.01.048 (abstract)paper