Brewing Sake Rice Wine — Parallel Fermentation with Koji

Wash the polished rice in cold water repeatedly until the water runs clear — this removes surface starch that would make the sake cloudy and harsh. Soak the washed rice in cold water for 1-12 hours depending on the degree of polishing (more polished rice absorbs water faster). Drain completely for 30 minutes. Steam the rice (do not boil — boiled rice becomes mushy and gummy) over vigorously boiling water for 45-60 minutes. Properly steamed rice is firm on the outside but soft in the centre. Spread the steamed rice on a clean surface to cool to approximately 30 degrees C. Divide the cooled rice into three batches for the three-stage addition process (san-dan-jikomi).

Combine the first batch of steamed rice (approximately 20% of total), an equal amount of koji rice, water, sake yeast, and a small amount of lactic acid in the fermentation vessel. The lactic acid (in the modern sokujo method) suppresses harmful bacteria while the yeast population builds. Stir twice daily. The starter ferments vigorously for 10-14 days at approximately 15-20 degrees C, building a dense yeast population (approximately 300 million cells per millilitre). The moto is ready when it tastes sweet-sour and smells yeasty with a clean, slightly fruity aroma. This concentrated yeast starter is the engine that drives the main fermentation.

Over three days, add the remaining steamed rice, koji, and water to the moto in three progressively larger additions. Day 1 (hatsuzoe): add the second batch (approximately 30% of total rice and koji plus water). Day 2 (odori): do nothing — this rest day allows the yeast to multiply and catch up with the new food supply. Day 3 (nakazoe): add another addition (approximately 30%). Day 4 (tomezoe): add the final and largest addition (remaining 20% of rice plus koji and water). Each addition roughly doubles the volume. This staged approach prevents overwhelming the yeast — a single large addition would dilute the yeast too much and allow bacteria to gain a foothold.

After the final addition, cap the vessel with an airlock and ferment at 10-15 degrees C for 18-25 days. The low temperature produces a slower, cleaner fermentation with more delicate flavour compounds. During this period, the koji enzymes continuously convert rice starch to glucose (saccharification) while the yeast simultaneously converts that glucose to alcohol (fermentation). This parallel process is unique to sake production and is why sake achieves higher alcohol than wine or beer. Stir the moromi once daily for the first week to incorporate the koji evenly, then leave it undisturbed. The fermentation is complete when bubbling slows to less than one bubble per minute and the moromi tastes dry with no residual sweetness.

Strain the finished moromi through cheesecloth or a nylon mesh bag, pressing gently to extract the sake. The pressed liquid is cloudy (nigorizake). For clear sake, allow it to settle for 1-2 weeks in a cool place, then carefully siphon the clear liquid off the sediment (called racking). Pasteurise by heating to 62-65 degrees C for 10-15 minutes to kill remaining yeast and enzymes, halting any further fermentation. Store in sealed glass bottles in a cool, dark place. Fresh sake (namazake, unpasteurised) should be refrigerated and consumed within weeks. Pasteurised sake improves with 2-6 months of ageing as harsh young flavours mellow and integrate. Serve chilled, at room temperature, or gently warmed depending on the style.