Notes
Koji is made by cultivating a mold on a cooked grain or legume substrate. It is central to traditional Japanese fermented foods like Miso, Soy Sauce, Sake, Amazake, Shochu, and Mirin. This exploration focuses on using koji to transform regional ingredients from the Northeast into complex sources of flavor, sweetness, and umami, with an additional goal of developing a gluten-free option.
Microbiology & Enzymes
- Aspergillus oryzae: The most common koji variety. Strains are selected either for high protease activity (ideal for miso and soy sauce) or high amylase activity (ideal for sake and amazake).
- Aspergillus sojae: Commonly used for miso and soy sauce.
- Aspergillus luchuensis: Produces citric acid; traditionally used in shochu production.
- Enzymatic Activity: As the mold grows, it secretes enzymes to break down the substrate:
- Proteases break proteins into amino acids and peptides (e.g., salt-tolerant alkaline proteases in high-salt ferments; “Flavourzyme” is an A. oryzae-dervied protease blend used for industrial enzyme applications.)
- Amylases break starches into dextrins and sugars.
- Lipases break down fats into fatty acids.
- Pectinases and other specialized enzymes are also produced depending on the strain and substrate.
These enzymes can have a variety of interesting and productive specialized use cases. The dextrins produced by amylases, for example, are often used independelty to prevent bread staling; by adding amazake to a bread base, you can mimic this effect. Otherwise, the combination of amino acids as the result of proteolysis and sugars is responsible for many of the key flavor precursors in foods such as chocolate and coffee; these enzymes can be creatively used to create chocolate and coffee tasting alternatives and a variety of unique aromatic compounds depending on the substrate.
Substrates While polished rice is the traditional substrate, regional grains are being evaluated to establish local sources of sweetness, umami, and enzymatic activity:
- Renan Wheat (pearled)
- Farro (pearled)
- Oats
- Sorghum
Preparations
Grain Substrate Trial
- Pearled Renan Wheat, Pearled Farro, and Oats: Soaked overnight, then steamed for 30 minutes.
- Results: Strong, successful koji growth on all three.
- Sorghum: Boiled until soft enough to press easily between the fingers.
- Results: Poor growth. The dense grain structure and intact hull made penetration difficult for the mold.
Ideas
- Mechanical Processing: Test cracked versions of the grains or lightly blitz them in a food processor prior to inoculation to expose the starch-rich interior and bypass the fibrous hull.
- Nixtamalization: Explore nixtamalizing sorghum to help break down its tough outer hull and improve mold penetration.