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1
Cook the rice with water to a fully softened porridge (okayu) texture. The grains must be entirely tender and cohesive — no firm centre, no al dente resistance. Dry or undercooked rice reduces the surface area available to the koji enzymes and produces uneven saccharification. The porridge is ready when a spoon drawn through it leaves a slow-closing channel.
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2
Allow the cooked okayu to cool until it registers 55–60°C throughout. This temperature window is where the dish lives or dies: above 65°C the koji enzymes are irreversibly denatured and the result is plain rice porridge; below 50°C saccharification slows and unwanted bacterial growth becomes a risk. Use a probe thermometer and adjust as needed before proceeding.
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3
Combine the cooled okayu with the fresh koji, mixing thoroughly so the koji is evenly distributed through the porridge. Transfer to a rice cooker set to 'keep warm' (typically 60°C). Rest with the lid ajar for 8–10 hours. The ajar lid prevents heat from climbing above 60°C while allowing slight moisture release.
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4
At the 8-hour mark, taste the mixture. It should be distinctly, naturally sweet and thick — the starches converted to glucose and maltose by the koji. If it remains starchy and bland, the enzymes have been inactive through a temperature error and the batch cannot be recovered. A successful amazake carries a milky, warm, subtly fermented grain depth beneath its primary sweetness.
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5
To serve hot, transfer to a saucepan and warm gently to just below a simmer, stirring. Do not boil: sustained high heat will continue to alter the enzyme-produced sugars and flatten the flavour. The amazake is ready to pour when it is steaming, fluid, and ivory-white, with a faintly grainy texture in suspension.
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6
To serve cold, chill the finished amazake and pour directly. For a cooking application as a glaze or marinade component, brush directly onto fish or chicken before grilling, or reduce uncovered over low heat — removing approximately 30% of volume — to produce a concentrated paste suitable as a natural sweetener in confections. The reduction is complete when the paste coats the back of a spoon and holds a line drawn through it.