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Fermentation Atlas

Fish and seafood from Japan

Kusayaくさや

Split, gutted fish such as mackerel scad and flying fish are soaked for 10 to 20 hours in kusaya-jiru, a brown, smelly brine that has been reused and topped up for more than a century, then rinsed and dried in the sun. Bacteria living in the old brine give the fish its strong smell and help it keep about twice as long as ordinary salted dried fish. Made in 3 steps over 10 h – 20 h. The longest step, soak in kusaya-jiru, takes 10–20 h (Fujii T. 1999). Salt is 2.7–11.1 % (Fujii T. 1999). "Corynebacterium" and Marinospirillum spiral bacteria do most of the fermenting.

Key numbers
Main step10–20 hReported[fujii1999]Soak in kusaya-jiru
Salt2.7–11.1 %Measured[fujii1999]Soak in kusaya-jiru
Fully documentedFish and seafood10 h – 20 hMore fish and seafoodMore from Japan

Recipe

No fixed amounts recordedTraditional process with no fixed amounts; the fish are simply immersed in the house brine.
Fresh, lean fish (aomuro, muroaji or tobiuo), split, gutted, washed and bled[fujii1999]
Kusaya-jiru, the house brine kept for generations · Salt content varies by island[fujii1999][masaki2026]
Starter: backslop (the brine is reused with no added culture)

Total time across the recorded steps: 10 h – 20 h

Start
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What changes: The fish are split, gutted and washed until the blood is gone

Step 1 of 3
Split, gut, wash and bleed the fish
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented

Output: split, drained fish.

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

What makes this one different

Kusaya is made like ordinary salted dried fish, but the fish soak in an old, living brine instead of fresh salt water. The brine's bacteria give the smell and slow spoilage.

Related ferments

Variants

  • Hachijōjima kusayaSaltier brine (8.0–11.1 %) with a different microbial community and sulfur-rich smell.
  • Niijima kusayaLower-salt brine with no trimethylamine detected and short-chain fatty acid aromas.

Safety

E. coli, Vibrio parahaemolyticus and staphylococci were not found in kusaya brine, and kusaya keeps nearly twice as long as salted dried fish made from the same fish. Streptomyces from the brine make compounds active against moulds, yeasts and bacteria.

History and sources

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

Islanders salted fish for drying and had to reuse the same brine again and again; over time it took on a strong smell and the fish dipped in it did too. It became a valued preserved food on the islands.

  1. [fujii1999] Fujii T. 1999, 魚介類の保蔵から生まれた発酵食品 (fermented seafoods born from fish preservation), review, 日本食品保蔵科学会誌 (Food Preservation Science) 25(5):245paper
  2. [fujii2016] Fujii T., Kyoui D., Takahashi H. et al. 2016, Pyrosequencing analysis of the microbiota of kusaya gravy obtained from Izu Islands, International Journal of Food Microbiologypaper
  3. [kita2023] Kita K., Unno R., Osada T. et al. 2023, Relationship between microorganisms and volatile components in each fermentation process in the kusaya gravy, Bioscience, Biotechnology, and Biochemistrypaper
  4. [masaki2026] Masaki S., Ogaki S., Kanayama N. et al. 2026, Salt-induced 7-deoxypactamycin and oligomycin production in Streptomyces sp. strain TUA-HK1GM isolated from kusaya gravy, Journal of Antibioticspaper
  5. [s1] Wikipedia, Kusaya (serving only)wiki