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How
to Make KOJI Successfully
Koji refers to the grains on which a fungus named Aspergillus Orizae or its close relative such as Aspergillus Luchuensis is grown. Koji is essential to making miso, soysauce, sake, shochu, amazake, mirin, and shio-koji. Many people think koji making is difficult. Even professional koji producers tend to discourage ordinary people to make koji by themselves. This article teaches, however, how to make koji easily and successfully. There are 3 kinds of koji: white koji, yellow koji, and black koji. Black koji is used to produce citric acid, black vinegar, and Awamori shochu. Recently, black koji is attracting attention because amazake made using black koji has slight acidity and very pleasant. White koji is most suitable for making miso, shio koji and amazake. Yellow koji is recommended for making sake and shochu. However, white koji and yellow koji are exchangeable although flavors of the products become somewhat different. In making sake and shochu, using the yellow koji is recommended except in hot seasons. Yellow koji gives better flavor to sake and shochu than white koji. However yellow koji tends to be unstable in hot seasons. So if sake or shochu is to be made in hot seasons or in hot regions, white koji should be recommended. Indeed, in the hot regions of Japan where many shochu makers are located, most of shochu makers use white koji to produce shochu. White koji starter (Shirokoji Shirayuki Komachi), yellow koji starter (Mototate), and black koji starter are available at Etsy.com as of June 2022 (see the following photos). The following photos are images of koji fungi under a microscope.
Koji photo under microscope (1) (2 days after inoculation) Fibrous growth of koji fungi
Koji photo under microscope (2) (5 days after inoculation) Spores at the end of fibers Materials Rice 5 cups (about 1000 g). Short grain rice produced in California is highly recommended. Koji starter (seeds, or spores) 1/2 tsp Steam cooker Flat plastic vessel with a lid (suggested size: 8 x 13 x 4) Warm place, or incubator (28 - 30 C) Procedure (applies to all kinds of koji starter)
· Wash and soak 5 cups short grain rice for 5 to 6 hours. (Previously 90 minutes of soaking was recommended, but after many tests, soaking for 5 to 6 hours was found to produce far better results.)
· The readers can work with a different amount (than 5 cups of rice) depending on the size of the steam cooker. In this case, change the amounts of other ingredients proportionally. The fermentation vessel explained above works up to 5 cups of rice at a time. The height of the steamed rice in the fermentation vessel should at least 3 cm. If the height of rice in the fermentation vessel is too low, koji growth becomes slow. Therefore, for a small amount of rice, use a small fermentation vessel. · Steam cook at a strong heat for 60 minutes. · Make sure that the steam cooker has ample water in the boiler. · The procedure to make koji explained here applies to any kind of koji including white, yellow and black.
· Cool down to 40 C or 104 F, or lower, after the steam cooking. Transfer the steam-cooked rice to the flat fermentation vessel.
· Inoculate rice with ample koji spore. Wrap the koji spores in a 3 inch square gauze, and shake-sprinkle uniformly from 3 4 inch high position. Mix and repeat shake-sprinkle until all the koji starter in the gauze is gone. Be careful not to inhale the koji spores. If koji spores are inhaled, koji fungus may grow in the lung. · A key for success is to use ample koji starter than written in the koji starter envelope. 10 g koji starter is sold to make 15 Kg koji. This rate is for professionals, however, who can control moisture, temperature and supply of air exactly. To the novices who cannot do this well, the best approach is to use ample koji starter, say 3 to 4 times of the rate for professionals. That is, use 10 g koji starter to make 4 Kg of koji rather than 15Kg. This will make making koji far easier. · Mix the inoculated rice by hand and rub between two palms so the koji spores adhere to the surface of rice grains. Mix the whole again. · Place the fermentation vessel in a warm place (28-30 C). An incubator as shown in the figure below can be used, which is a card box installed with a 25 W lamp and Styrofoam block on each side of the lamp. The plastic containment is placed above the Styrofoam blocks.
The author recently installed a thermostat switch (shown below) to control the power supply of the lamp so the temperature at the bottom of the vessel is kept closely to 28 C. The temperature sensor is placed under the fermentation vessel. The model shown below costs about $35 at Amazon. A less expensive temperature control ($15 at Amazon) is shown below: Keep in mind that the above model is limited to 42 C degrees, which is OK for koji making, but cannot be used for making amazake. · Alternative approaches include (1) using an electric blanket, and (2) using a picnic cooler with an electric heating pad. In each case, using an thermostat switch set to 28 to 30 C is highly recommended. In hot summer, you do not need such heating device. Just placing the fermentation vessel in a garage would work well. · At any rate, observe the rice in every 12 hours. Purposes of observation are (1) finding the condition of koji growth, and (2) to supply fresh air to the vessel. If the rice is lumped together, flip the whole content upside down. This will ensure supply of fresh air. · When 48 hours are past, all the grains should be covered with koji fungus. If this stage is not reached, continue, for another 12 to 24 hours. Biochemical
reactions that take place in making koji is
exothermic, that means, the koji fungus
absorbs oxygen and generate heat. If too much heat is generated, the koji becomes too hot and may destroy whole koji. Therefore, the temperature of the
incubation chamber should not be too high, and occasional observation of the
condition of the koji grown is necessary.
If everything goes successfully, the completed koji should look like the following photo.
· If koji is left unused for two to three more days, spores will develop, which look green if the koji is yellow koji kind, but spores are just white if the koji is white koji kind.
The quality of koji for sake fermentation becomes poor if this stage is reached. Dont be discouraged if you fail in the first or second attempts of making koji. If you fail, think what might have made your attempt fail. Try again with improved work, and you will succeed. Use of Aquarium Air Pump The author recently started using an aquarium air pump available at Amazon.com for less than $10 as illustrated in the figure below:
The outlet of the air pump is connected to a plastic pipe and led to the bottom of the incubation vessel through a hole at the center of lid of the vessel, so air is discharged at the bottom of the incubation vessel. With this air supply, the lid is not slightly opened any longer but completely closed. Also there is no need to open the lid once in every 12 hours to check the progress of fermentation. With this approach, the vessel should be filled to the top without leaving a space near the top. In other words, a tight vessel may be used. Of course the incubation vessel is placed at around 30C environment. Because of
the good supply of air and with the moisture that does not escape, koji fermentation goes very fast, and temperature inside
the vessel reaches nearly 40C. The koji
fermentation is nearly complete after 12 hours of incubation,
that is nearly 12 to 18 hours earlier than without the air pump. Barley
Koji and Soy Koji Making barley koji or soy koji
may be desired. In both cases the procedure is the same as described above
for rice koji.
The shirayuki komachi
koji starter may be used for both cases. The procedure mentioned above for the rice koji may be applied to barley koji without any alteration. The same for soy koji making, except one thing. The soy steamed for 1 hour after soaking over night is not soft but too hard to eat. That is OK in making soy koji. It may take much longer to ferment soy, but be patient. It may take three or four days. What
you should not do A. If the koji produced is left for a few more
days, it will be covered with spores. When this stage is reached, a small
amount of it may be used (with or without complete drying) as koji starter for the next batch of making koji. And this can be repeated over and over in a cycle. However, this is potentially a very dangerous practice, because the koji spores may be contaminated with toxic species such
as Aspergillus Flavus,
which is very similar to Aspergillus Orizae, but comes from the air. The chance and amount of
this kind of contamination increase as the use of spores from the previous
cycle is repeated. The best practice is to use the koji starter
purchased from a trustable maker. Koji makers produce koji
starter in a purifying environment using camellia ash. The koji made in this way is approved to be safe by FDA and
WHO. B. Recently the number of website that explain how to make koji has increased dramatically. Unfortunately many of them have some false information. First, often koji starter is sprinkled using a tea strainer, which consumes unnecessarily large amount of koji starter. In order to spread this amount uniformly on the steamed rice, the best way is to wrap koji starter in double layer of gaze of 4 inch square. Hold the edges of the gauze and shake on the steamed rice. Then, rub the rice by both hand so the spores are well adheres on the rice surface. Repeat shaking and rubbing the rice. Repeat until all the koji starter is consumed. Second, often the temperature of fermentation is too high, like 35 to 40 C. Then, because koji generates heat while being fermented, the temperature may reach 45C at which koji fungus may die. I recommend to set the fermentation temperature to 28 to 30 C. With this range of temperature setting, these is no risk of the temperature reaching too high, yet koji is completed in less than 48 hours. This note was revised in June 2023. Authored by S. Nakamura Other manuals relevant to koji, including that of miso, are available in the following book: Handbook of Making Sake, Shochu, Koji, Amazake, Miso, Natto, Mirin and More Second Edition, Authored by Shoichiro Nakamura, Published by Amazon.com, 2023 |
Steamed rice in a plastic fermentation vessel
