Background
Katsuobushi-style preservation can be adapted to many raw materials—as Noma has shown with pumpkin-bushi and — but every stage needs ingredient-specific tuning.
The baseline process involves:
- Steaming: Steam the prepared pieces at 90–100 °C until their core stays above 90 °C for 20–30 minutes to gelatinize starches, set proteins, and drive off surface moisture without letting soft vegetables collapse.
- Smoking and Drying: Dry and smoke in repeated hot-smoke cycles. Hold the blocks at 60–75 °C for 6–8 hours per session using a mild hardwood (such as cherry or oak), with overnight rest periods to allow internal moisture to migrate outward. Total smoke time can range from 24 hours for delicate produce up to 100 hours for fish. Humidity must be kept below ~60%; move racks to a dehydrator or ventilated room if damp weather stalls drying.
- Inoculation: When moisture content falls below ~25%, inoculate the surface with a light mist of koji mold (traditionally Aspergillus glaucus for fish, but aspergillus oryzae performs reliably on vegetables).
- Aging: Age the blocks at 15–20 °C and ~65% relative humidity for one to three months, brushing off the mold bloom, re-smoking briefly, and re-inoculating between cycles. Three to four rounds leave the product rock-hard, shelf-stable (water activity < 0.75), and intensely savory.
Method
To adapt this process for a simplified trial, I am going to run the following experiment:
- Prep and Salt: Vacuum-seal the vegetables with 2% salt by weight. This will prevent excess fermentation and inhibit undesirable microorganisms during the incubation period. Leave for a few days.
- Inoculation: Remove the vegetables from the bags, pat them dry, and inoculate them with Koji.
- Incubation: Incubate for 24–48 hours.
- Finishing: Dry the inoculated vegetables, smoke them, and then dry-age them in the fridge for a few days.
Notes and Observations
- Process Deviations: Unlike the traditional method, I am not going to repeatedly inoculate the substrate, nor will I spray them with a spore mist, and the smoking will take place after the fermentation.
- Penetration Concerns: The primary concern is not getting adequate mold growth in the middle of the vegetables or having too much moisture which will prevent adequate koji growth.
- Alternative “Cake” Method: To counter potential issues with internal mold growth, I will run some parallel tests where the vegetables are cut into small pieces and dried slightly to mimic the moisture content of grain. They will then be inoculated and pressed into a cake, which will undergo the same smoking and drying process.
Initial Substrates for Testing
Future Adjustments
If these initial trials prove successful, we can expand the experiment to include mushrooms or various grain varieties.