Stephanie Houng

What is Koji? A Guide to Making Koji

Koji mold is essential in making many traditional Japanese foods and helps in breaking down starch in the rice.

koji rice on blue table

Koji mold is essential in making many traditional Japanese foods. It plays a crucial role in fermentation worldwide.

For centuries, Japan has used Koji to create sake (Japanese rice wine), miso paste, and pickles. These foods aren't just tasty; the Koji fermentation process produces many health-boosting compounds.

Recently, studies have found even more health benefits from Koji compounds.

These include enzymes and amino acids good for the skin, plus antioxidants and vitamins that promote healthy skin and can reverse aging signs.

This article dives deep into Koji's history, biology, and uses in both traditional and modern contexts.  We'll answer common questions such as:

"What is Koji?"
"How to make Koji?"
"What is Aspergillus oryzae?"
"What are the different types of Koji"
"Why is Koji needed to ferment rice into Sake and nutrient-rich Sake Kasu?

We'll also share insights from scientific research and traditional practices.

Why Koji is Needed in Fermentation?

In order to make alcohol, yeast needs a source of sugar. For instance, red wine is created when yeast ferments the sugars in grapes into wine. Rice, on the other hand, is mostly made up of starch and is a poor source of sugar.

That’s where Koji comes in. The Koji mold helps break down the starch in rice into sugar that the yeast can then turn into alcohol.

Table of Content

  • History of Koji
  • Differences in Koji Varieties
  • Mastering Koji Production
  • Health Benefits of Koji
  • Is Koji Safe?
  • Recipes Incorporating Koji
  • Using Koji for Skincare, Beauty, and Health

History of Koji

making sake in japan

Koji mold, primarily derived from the spores of Aspergillus oryzae, is known in Japan as "kikōji-kin." It has been a cornerstone of Japanese fermented cuisine since as early as the seventh century.

Early Origins of Koji

Koji mold's history is linked to traditional Asian wine brewing

Koji mold's history is linked to traditional Asian wine brewing. It was first mentioned in the 6th-century Chinese text "Qiming Yaoshu," where koji was said to turn starch into sugar and alcohol with steamed grains (a process known as saccharification). By the 7th century, Japan had started to use koji for early sake brewing, starting with moldy rice at home.

Meanwhile, other Asian countries had their own molds for fermentation: "qū" in China, "luck pang" in Thailand, and "ragi" in Indonesia. These early brewing methods were basic, and used naturally moldy rice without controlled processes. Koji also existed naturally in the environment.

Where did Koji come from?

Koji mold naturally existed in the environment in Japan and was used for all types of fermentation for centuries.

Koji Development in Japan

The first controlled method of making sake was recorded in the 8th-century text "Engishiki."

Before this, people used naturally moldy rice for fermentation. In the 8th century, the Japanese began to actively inoculate steamed rice with koji spores. Back then, brewers needed over 100 times more spores than they do today to get the same results.

This shows how inefficient the process and yield were by modern standards.

Then starting in the 9th century, the Japanese worked to improve the quality and safety of the koji starter. They added wood ash to the koji mixture, which acted as fertilizer for the mold and helped the koji grow on the rice. The carbon in the ash also sterilized the mixture, reducing unwanted bacteria growth. This method was so effective it continued until the 1800s.

Koji was called 友種 “tomo-dane” in Japan, which translates to “friend of the seed”.

malting rice with koji

Technological Advances in Koji Making

Each sake brewery made its own koji, and koji starters were rarely sold outside their local towns. It wasn't until the late 1800s that koji became more widely available.

Before this, people didn't fully understand what was in the "koji" spores they used. They knew that sprinkling koji on rice caused fermentation, but the mixture was impure and pathogenic. It contained Aspergillus oryzae (koji mold) along with other microorganisms like yeast, bacteria, and competing molds.

During the Meiji era (1868-1912), koji starter became commercialized, improving its use and production. Then technological advances in the 20th century allowed scientists to specifically isolate beneficial and desireable strains and develop better cultivation techniques.As a result, the quality and consistency of koji starters significantly improved.

Not only did Koji technicians improve the quality of Koji, they identified various strains for different fermentation purposes. Early koji starters were impure, and contained various microorganisms that made them pathogenic. Detailed studies in the mid-1800s isolated pure Aspergillus oryzae, leading to cleaner koji starters for rice.

Later in the 1900s, other strains of koji were identified. While Aspergillus oryzae was ideal for rice fermentation, other strains were more effective for producing soy sauce, miso, or natto.

Early koji starters were impure and often contaminated with harmful bacteria and competing mold spores. It wasn’t until the mid-1800s that researchers began to closely examine koji mold and took steps to isolate its beneficial and desirable components.

Aspergillus oryzae was ideal for rice fermentation, other strains were more effective for producing soy sauce, miso, or natto.

Before the 1800s, each sake brewery had its own unique koji starter, often kept as proprietary family secrets passed down through generations. Today, most sake brewers around the world rely on koji from 12 exclusive koji producers who have spent centuries perfecting their craft. These specialized producers make koji year-round, continuously investing in improving its quality and developing new strains for various uses, including skincare. Their years of dedication and expertise have led to a level of koji that no one else can replicate.

Koji mold has come a long way, from its start as a wild fungus into a key component in industrial fermentation. This journey really shows just how important koji has been throughout Japanese history and how its significance continues to grow globally today. Its ongoing development also proves how incredibly versatile and applicable it is across so many different industries.

In the past, Koji was cultivated individually at each sake brewery. Then in the 1800s, researchers began to improve the quality of koji starters and developed new strains of koji to improve the yield and expand its application.

Different Koji Mold Varieties

What is Aspergillus oryzae?

Koji is needed to break down the starch in the rice into sugar. In sake fermentation, yeast is then added to turn the sugar into alcohol. However, koji mold in fermentation isn't limited to the mold species Aspergillus oryzae.

The following three species —Aspergillus oryzae, Aspergillus sojae, and Aspergillus luchuensis— are the main types of koji used in Japan. Scientists have created over 40 variants within these species, each producing different fermentation results.

Aspergillus oryzae:
Adept at breaking down the starch in rice, making it ideal for making Japanese sake. It breaks down the rice without imparting unwanted flavors or aroma, so is favored by sake brewers.

Aspergillus sojae:
Predominantly utilized in brewing soy sauce and miso due to their specific enzymatic activities that are great at breaking down the protein in soybeans into other essential compounds necessary for fermentation.

Aspergillus luchuensis:
This koji is black (called “Kuro Koji” in Japan) and likely a native variety of Koji from Okinawa. It’s predominately favored in the production of distilled spirits like shochu and produces more citric acid than the other varieties, making it have more anti-bacterial properties.

koji mold spores
koji varieties

Koji in Fermented Foods and Beverages:

Koji mold plays a fundamental role in producing a vast range of products such as sake, shochu, soy sauce, miso, and more.
Each of these products benefits uniquely from the enzymes produced by koji mold, which contribute to their distinctive flavors and nutritional profiles.

How Many Different Types of Koji Are There?

There are 3 main species of Koji which are used for fermentation in Japan: Aspergillus oryzae, Aspergillus sojae, and Aspergillus luchuensis.

Studies show that koji mold enzymes not only improve taste but also boost the nutritional value of foods by increasing amino acid levels, adding health benefits.

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Mastering Koji Production

Evolution from Ancient Methods to Modern Techniques

Traditional koji production relied on natural inoculation, where grains were exposed to air to capture naturally occurring molds.

Modern methods inoculate steamed grains with cultivated koji spores under controlled conditions to optimize growth and enzyme production.

innoculating koji into rice

Step-by-Step Guide to Making Koji

Making your own koji starter is a very intensive process, and cultivating your own koji spores is even more demanding, requiring precise instruments and environments.

We recommend buying dried koji rice starters from reputable retailers.
However, if you want to make your own, follow our step-by-step guide vetted by sake brewers in Japan.

We advise against cultivating your own koji spores because it’s easy for them to become contaminated. Even professional sake brewers no longer cultivate their own koji spores because of the difficulty. It's much safer and faster to buy koji spores from reputable sources.

For recommendations on where to buy dried koji starters or spores, you can contact us or watch our DIY fermented rice water video.

Step1: Gather Your Materials

To make koji, start with a cereal grain for the mold to grow on, traditionally rice, barley, or soybeans.

Remove the outer shell and polish the grain to expose the nutrient-rich part. Polishing can increase koji yield by 10-20%.

Powdered Rice vs Whole Rice

You can use powdered grains, which also increase yield due to more surface area. However, powdered grains have a higher risk of bacterial contamination. Therefore, most commercial koji makers prefer polished whole grains.

Short vs Long Grain Rice
Short grain rice has a higher starch content which helps the Koji grow. Long grain rice (such as jasmine rice) have lower starch content which leads to a slower and less efficient koji cultivation process.

types of rice for koji

Does it matter what type of container you make the Koji in?

Traditionally, koji has been made in Japanese cedar boxes, but nowadays, stainless steel and plastic containers are also used. Recent studies have highlighted a few differences between these materials:

Wooden Containers:
- Koji made in wooden containers tends to stay whiter for longer and doesn't turn yellow until later in the cultivation process.
- The roots of the mold, known as hyphae, penetrate deeper and grow longer in wooden containers, which is preferred. This may be because it takes longer for the koji to grow in wood.
- Slightly preferred for making koji due to these qualities.

Stainless Steel and Plastic Containers:
- Both materials help maintain the moisture content of the koji better than wooden containers.
- Koji grows faster in stainless steel and plastic containers.
- No significant differences in the enzymes created or in koji growth between stainless steel and plastic containers.

Overall, while stainless steel and plastic containers offer advantages in moisture retention and growth speed, wooden containers are slightly preferred for the deeper and longer hyphae they produce, which can enhance the final product.

Key Takeaways

You can use various grains and legumes for your base, but if you are using rice it's best to use polished short grain white rice.
Use a wooden box for optimal koji growth.

maintaining koji moisture content

Step 2: Maintain the Moisture Level

Depending on the environment and strains, Koji usually takes anywhere from 2-6 days to grow.

For Koji to grow effectively, the grow media that the koji mold consumes (such as rice, barley, or soybeans) needs to have a moisture content of around 40%.

This is why the rice is steamed first: to provide enough moisture for the koji, and to soften the grain to allow the koji hyphae to penetrate the material.

If the moisture level drops below 30%, koji growth slows down. But if the moisture goes above 50%, you risk rapid bacterial contamination. So, keeping the moisture just right is key!

Key Takeaways

Maintain a moisture content of 40%. If the moisture level goes below 30%, koji growth will stop. If the moisture level goes above 50%, you have a high risk of bacterial contamination.

koji innoculation

Step 3: Inoculating the Koji

Koji mold has a long growth phase, which makes it prone to contamination by other molds and bacteria. The optimal growth temperature for koji is between 35-38°C (95-100°F), but unfortunately, this also creates a perfect environment for bacteria to thrive and contaminate your batch.

For the best results, start growing your koji at 30-32°C (86-89°F) with 40% water content. As the koji starts consuming the base material, the heat will naturally rise to around 50°C (122°F). Just be sure to keep an eye on the temperature — if it goes above 40°C (104°F), the spores could start to die.

Key Takeaways

Making koji is a battle against bacteria. Making sure the koji mold thrives while keeping bacterial growth in check is the key to creating great koji.

culturing the koji

Step 4: Culturing the Koji

Afterwards, spread the koji-inoculated rice out into a 50-60 cm thick layer to prevent it from drying out. Place it in a room at 30°C (86°F).

In about 24 hours, you should see white koji hyphae on top, and the temperature should reach up to 40°C (104°F). Lightly mix the material to circulate oxygen and lower the temperature.

Put the koji in a wooden container, spreading it evenly so the rice is 1-2 cm thick. Keep it in a temperature-controlled room at 30-32°C (86-89°F) with 40% moisture. If maintaining moisture is tricky, drape a clean, moist cloth over the box to help lock in the moisture, and replace it daily.

After the initial mixing, let the koji grow undisturbed. Avoid mixing or using a fan, as this can disrupt spore formation.

Let the mixture rest for another 12-24 hours until the koji is ready and still white.

Key Takeaways

It’s recommended that you do NOT cultivate your own Koji spores, as it is extremely difficult to achieve the quality and purity that you want. Use the Koji starter while it is still white and before the spores flower and the koji turns yellow.

Only proceed past here if you have the necessary equipment.

Step 5: Drying out the Koji for Cultivation

To cultivate the spores, wait another 3-4 days until they form and the koji turns yellow.

The moisture content should be 32-40%. The goal is to reduce it to less than 10% without killing the mold.

Use a warm air dehumidifier. Set it to 40°C (104°F) and 10% moisture. Avoid harsh airflow or fans to prevent spores from scattering. This drying process takes about 40 hours. Once dried, store the koji in a cool, dry place at 10-15°C (50-59°F).

Make sure you have a warm air dehumidifier. Put the koji mixture in the warm air dehumidifier and set the temperature to 40°C (104°F) and moisture level set to 10%. The spores can easily scatter so minimize harsh airflow or fans blowing over the koji. This drying process will take around 40 hours. Once dried, the koji in this dried form can be stored in a cool dry location where the temperature is between 10-15°C (50-59°F).

You can use other methods like freezing, but most koji makers prefer a warm air dehumidifier for its ease and effectiveness.

Drying out Koji

Key Takeaways

Drying out the Koji gradually without killing the Koji spores is tricky and should only be done if you have the right equipment.

There used to be 43 companies belonging to the Japanese Koji Association, but currently there are only 12 companies left. And out of the 12, only 6 companies make Koji on a larger scale to sell nationwide. Each company has extensive laboratories and quality control teams, and partners with research companies and universities to ensure quality.

cultivating and storing koji rice

Step 6: Cultivating the Koji mold spores and storing

To extract koji spores, use a fine US100 size mesh (0.149 mm). Gently sieve the spores through the mesh.

Then collect the spores and seal them in an airtight container. Store the container at -20°C (-4°F).

Keeping a close eye and making adjustments during fermentation is key to making sure your koji mold grows perfectly. It’s also absolutely essential to buy koji spores from a reputable supplier to make koji rice!

Key Takeaways:

You can NOT make koji rice by just leaving steamed rice or rice water out at room temperature.

For safety reasons, we recommend that you buy koji spores from a koji producer in order to make koji rice, rather than cultivating your own koji


You might have seen tutorials on TikTok and YouTube suggesting a simplified way to make "fermented rice water" by rinsing rice and leaving it on the counter or in the fridge. Unfortunately, that's false information. Similarly, you cannot make koji rice by just leaving steamed rice or rice water out at room temperature. For authentic koji rice, you need to follow the proper steps and use quality koji spores.

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What are the health benefits of Koji?

Koji mold breaks down complex molecules to help its growth. This process creates simpler, beneficial compounds. These compounds are a treasure trove for health and skincare.

Fermented rice water made from koji is considered to be the “fountain of youth” in Japan.

So, what are some of these beneficial compounds?

Koji Process

Enzymes found in Koji Fermented Rice:

These enzymes break down proteins into amino acids and peptides, making it easier for your body to absorb nutrients. They can also reduce allergenic properties in foods.

Skincare Benefits of Protease: These enzymes can exfoliate the skin by breaking down the proteins that cling onto dead skin cells. This promotes cell renewal, leading to smoother, clearer skin.

These enzymes break down starches into simpler sugars like maltose and glucose, aiding digestion and enhancing the sweetness of fermented products.

Skincare Benefits of Amylase: Can contribute to skin health by improving overall digestion and absorption of nutrients, which supports a healthy complexion.

These enzymes are involved in the hydrolysis of fats, which means they’re turned into fatty acids and glycerol, aiding in lipid digestion.

Skincare Benefits of Lipase: Contributes to skin health by improving the overall digestion and absorption of nutrients, promoting a healthier complexion.

This enzyme breaks down phytic acid, a substance in grains and seeds that can inhibit the absorption of minerals.

Skincare Benefits of Phytase: By reducing phytic acid levels, phytase improves mineral bioavailability, particularly iron, zinc, and calcium. These mineralsare crucial for maintaining skin’s defense system, supporting collagen synthesis, and promoting the regeneration of skin cells.

Though less commonly associated with koji, lactase can be present in fermented products and is crucial for the digestion of lactose.

Skincare Benefits of Lactase: It can improve digestive health (including those who are lactose intolerant), which leads to better skin health. A healthy digestive system helps absorb nutrients necessary for skin health, reduces inflammation, and leads to clearer skin.

These enzymes break down beta-glucans, which are complex sugars found in cereals. This process helps clarify fermented products and supports immune health by enhancing the bioactivity of beta-glucans, known for their immune-boosting properties.

Skincare Benefits of Glucanse: By enhancing the immune response, glucanases can indirectly improve skin health. A strong immune system helps manage conditions like psoriasis and eczema, which are influenced by immune system activity.


Amino Acids and Peptides found in Koji and Fermented Rice:

Amino acids are the building blocks of proteins, and peptides are small chains of amino acids that have various biological activities. Here's a look at some key ones:

Glutamic Acid:
Enhances flavor (umami taste) and is an important neurotransmitter.

Skincare Benefits of Glutamic Acid: Helps to maintain moisture and can be beneficial for skin hydration and elasticity.

Skincare Benefits of Lysine: Essential for the production of collagen, lysine helps strengthen skin tissue, which is crucial for maintaining the skin's firmness and resilience.

An essential amino acid that’s needed for the production of proteins, other enzymes, and neurotransmitters.

Skincare Benefits of Tryptophan: Supports collagen and elastin synthesis, aiding in maintaining the skin’s smoothness and elasticity.

Skincare Benefits of Alanine: Used in skincare products as a conditioning agent, it helps balance moisture levels and prevents dryness.

Skincare Benefits of Arginine: Used in anti-aging skincare products because it helps to repair visible skin damage. It promotes collagen production and increases skin elasticity.

Skincare Benefits of Serine: Helps to strengthen the skin's natural barrier, keeping it hydrated and protecting against environmental pollutants and toxins.

Skincare Benefits of Threonine: Crucial for overall health, it helps maintain protein levels in the body, supports immune cell production, and strengthens the intestinal barrier.

Skincare Benefits of Proline: Crucial for protein synthesis and collagen production, it helps maintain and repair connective tissues. It contributes significantly to skin elasticity and firmness, while reducing the appearance of fine lines and sagging.

Skincare Benefits of Leucine: A branched-chain amino acid (BCAA) that is particularly important for muscle synthesis and repair. Helps improve skin's appearance by aiding in the repair and regeneration of skin cells and tissues. It can support the skin's recovery processes, which is beneficial in maintaining a youthful and healthy appearance.

Skincare Benefits of Valine: Crucial for muscle metabolism and coordination, tissue repair, and the maintenance of proper nitrogen balance in the body. Helps in skin management by promoting the health and repair of skin tissue. It also supports skin health by reducing the impacts of wear and tear and supporting overall vitality.

Peptides found in Koji and Fermented Rice:

Peptides are short chains of amino acids linked by peptide bonds, and they serve various important functions in the body and skin. Here are some key types:

Bioactive peptides:
Derived from proteins, these peptides have antioxidant, antimicrobial, and anti-inflammatory properties. They can help reduce the appearance of fine lines and wrinkles, offering potential anti-aging benefits.

Signal peptides:
These peptides send signals to different parts of the skin to trigger the formation of new collagen and elastin, which are vital for maintaining youthful skin.

Carrier peptides:
These help to stabilize and deliver trace elements that are necessary for skin health and enzymatic processes, promoting skin healing and renewal.

Neurotransmitter inhibitor peptides:
Often found in anti-aging products, these peptides reduce wrinkles by inhibiting muscle contractions under the skin, similar to how Botox works but in a more gentle manner.

Enzyme inhibitor peptides:
These peptides can slow down the rate at which collagen and elastin break down, helping maintain the skin's structural integrity and elasticity.

peptides in rice water

Vitamins & Minerals Found in Koji and Fermented Rice:

Koji and fermented rice are rich in vitamins and minerals that offer numerous benefits for both health and skincare. Here's a breakdown of these powerful nutrients:

Vitamin B:
Vitamin B such as riboflavin, niacin, and vitamin B6, are crucial for energy production and cellular metabolism.

Minerals like Zinc and Iron:
Zinc plays a crucial role in maintaining skin integrity, reducing acne flare-ups, and has anti-inflammatory properties. Meanwhile Iron helps proper oxygenation for a healthy glow and complexion.

Organic Acids found in Koji Fermented Rice:

Citric Acid:
Skincare Benefits of Citric Acid: 
Citric acid is popular in anti-aging and skin-clearing products for its ability to brighten skin, even out skin tone, and promote skin exfoliation and re-growth, which makes it popular in anti-aging and skin-clearing products..

Lactic Acid:
Balances gut microflora and improves digestion and nutrient absorption.

Skincare Benefits of Lactic Acid:
It’s also a popular alpha hydroxy acid (AHAs) that’s used in skincare to help reduce acne and the appearance of wrinkles and fine lines by promoting cell turnover. It's also known for its ability to increase the skin's hydration levels.

Acetic Acid:
Has antimicrobial properties and lowers blood sugar levels (particularly beneficial for people with type 2 diabetes).

Skincare Benefits of Acetic Acid:
Its antibacterial and antifungal properties help fight acne, eczema, and skin infections. It also conditions the skin by lowering pH levels and promoting the skin’s acid mantle, protecting against bacterial infections.

Kojic Acid:
Known for its antioxidant properties, kojic acid helps fight oxidative stress caused by free radicals, which can damage cells and lead to chronic diseases.

Skincare Benefits of Kojic Acid:
Kojic acid is popular in skincare for its skin-lightening properties. It inhibits the production of melanin, reducing hyperpigmentation, age spots, and scars.

You can read more in-depth about the benefits of Kojic Acid here.

Malic Acid:
Another component of the citric acid cycle plays a role in energy production. It can also help improve muscle performance and reduce fatigue.

Skincare Benefits of Malic Acid:
Malic acid is an AHA known for its exfoliating properties. It removes dead skin cells to uncover newer, more radiant skin. It also improves skin texture and tone.

compounds found in koji

The amount of beneficial compounds can vary significantly based on the material that’s used as a basis for the fermentation. The table below shows the difference in enzymes created by using various koji starters.

As shown in the table, you can use koji with various grains and legumes. However, different koji varieties excel at breaking down specific compounds. For example, Aspergillus oryzae is great at breaking down starch, while Aspergillus sojae is better at breaking down protein. Different koji strains also produce varying levels of beneficial compounds, so choosing the right one is key to getting the best results.

Key Takeaways:

Depending on the starter and type of koji you use, the fermentation process and compounds created can vary widely. Don’t be afraid to experiment with different ingredients! Just remember, the basic process (see section above) is the same no matter what ingredient you choose.


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Is Koji Safe?

Koji is mold right? So is it safe to eat food made with Koji?

Absolutely! Koji is completely safe to eat, similar to the mold found in blue cheese.

However, as mentioned multiple times, correctly creating a Koji starter and cultivating Koji is a battle against other competing bacteria and mold.

One common competing mold found worldwide you need to watch out for is Aspergillus flavus. Both Aspergillus flavus and Aspergillus oryzae (koji) are different molds found on rice. While Aspergillus oryzae is safe and produces beneficial compounds,Aspergillus flavus is very dangerous and can cause severe illness and even death.

Creating a Koji starter, cultivating Koji, and making Koji fermented rice water is a battle against other competing bacteria and mold.

So it's critical to prevent contamination. It's best to purchase professionally prepared Koji rice from a reputable supplier rather than making your own.

- Hatayama Natsuko

Dangers of Aspergillus Flavus

What is Aspergillus flavus? It is a fungus that poses significant health risks because it produces aflatoxins, which are among the most potent carcinogens known. Here's why it is particularly dangerous and why it’s commonly found in rice:

Here's why it is particularly dangerous and commonly found in rice:

Aflatoxins Production: Aflatoxins are toxic and carcinogenic compounds produced by Aspergillus flavus. Exposure can lead to liver cancer and other serious health problems.

Immunosuppressive Effects: Aflatoxins can weaken the immune system, making the body more susceptible to diseases and infections.

Impact on Growth: In children and animals, chronic exposure to aflatoxins can cause stunted growth and delayed development due to poor nutrient absorption.

Aspergillus flavus microscopy

Prevalence of Aspergillus flavus

Environmental Conditions:
 Aspergillus flavus thrives in warm, humid conditions, and is often found in rice-growing regions. Rice, when stored for long periods, can provide an ideal environment for this fungus, especially if stored in high moisture conditions.

Post-Harvest Contamination:
Rice can get contaminated with Aspergillus flavus spores during harvesting, handling, and storage. Once contaminated, the fungus can grow and produce aflatoxins, especially in conditions that favor fungal growth.

How Aspergillus flavus and Aspergillus oryzae are different

In 2005, genome sequencing of Aspergillus flavus and Aspergillus oryzae revealed that Aspergillus oryzae (koji) lacks the genes to produce aflatoxins, making it completely safe for consumption.

Aspergillus flavus is found worldwide, while Aspergillus oryzae is mostly found in parts of Asia, especially Japan.

The widespread presence of Aspergillus flavus (the harmful mold) causes many people to get sick each year from eating leftover rice. 

More recently, making your own DIY fermented rice water videos and tutorials have begun popping up all over Youtube and Tiktok. Unfortunately nearly all of these tutorials teach you the incorrect way to make so-called "fermented rice water", which can be extremely dangerous since they are just rancid rice water filled with aflatoxins.

Leaving cooked rice at room temperature can allow Aspergillus flavus to grow and release dangerous aflatoxins. It can also allow other dangerous bacteria such as Bacillus cereus, to contaminate the rice which can lead to food poisoning, characterized by symptoms such as vomiting and diarrhea.

Incorrect DIY fermented rice water methods can also result in aflatoxin-contaminated rice water.

Aspergillus flavus isn't just found on rice; it can also contaminate other grains and legumes like soybeans and peanuts. If these are left out too long, Aspergillus flavus can grow and produce harmful aflatoxins.

If by chance you get naturally occurring Koji to start propagating in your rice, it will most likely be contaminated with Aspergillus flavus and other competing molds.

A recent study analyzed contamination levels in koji rice made at home versus modern commercial methods. Homemade or traditional koji had up to 100 million bacterial and non-koji mold contaminants per gram of rice. In contrast, commercial koji had less than 1,000 contaminants per gram. This means home-made koji is 100,000 times more contaminated than commercial koji.

This highlights the importance of using professionally made koji mold spores and creating koji in a clean, sterilized environment. Making your own koji mold starters is inefficient and potentially dangerous.

Key Takeaways:

It's always advisable to buy professionally cultured koji, as homemade koji can contain 100,000 times more contaminants than koji from licensed producers.

Recipes Incorporating Koji

Koji is increasingly used for various things beyond traditional Japanese cuisine. This is because Koji serves two main functions:

(1) Koji helps break down compounds
(2) While breaking down the compounds, Koji produces over 300 other beneficial compounds (100 of which are amazing for your skin)

Because of these traits, many people are finding new, innovative ways to use Koji not only for food but also for health and beauty.

And specifically for food, Koji has been used in cooking for centuries due to its ability to break down compounds and add umami and complex flavors to food.

Marinating Meats

Koji is commonly used to marinate meats because it can break down proteins, tenderizing the meat and enhancing its umami flavors.

Recipe Idea:
Mix ground koji rice with soy sauce, mirin, and minced garlic. Marinate meats (such as chicken or beef) in this mixture for at least 8 hours before grilling or roasting. Koji helps tenderize the meat and enhances its flavor.

Koji Fermented Vegetables

Koji can break down compounds in vegetables, lightly fermenting them and adding a slightly sweet, nutty aroma and flavor. Unlike traditional pickles, koji-fermented vegetables aren't sour, making them a unique and healthy alternative that pairs well with delicate dishes.

Recipe Idea:
Mix ground koji rice with salt and pack it around the vegetables in a jar. Let it ferment for a few days at room temperature. The result is a unique, tangy, and umami-rich pickled vegetable.

Koji-infused Sauces

You can infuse Koji in many different types of sauces. Below are two different types of sauces that you can make using Koji.

Recipe Idea: Koji Miso Sauce
Blend koji rice with miso, sake, and sugar to create a flavorful sauce. Let the sauce sit at room temperature in an air-tight container for at least 24 hours. After 24 hours, mix the sauce and put it in the fridge to store. The sauce should smell slightly sweet and should have no sour smell to it. It can be stored in the fridge for up to 6 months. The sauce can be used as a marinade, a glaze for fish, or a dipping sauce.

Recipe Idea: Koji Soy Sauce
Mix ground koji rice with soy sauce and let it sit in an air-tight container for 3-5 days at room temperature. Mix the sauce every day to ensure the Koji gets fresh air. After 3-5 days, store the soysauce koji in the fridge for up to 6 months. The sauce can be used as a vegetable dip or a glaze for meat and fish.

Koji Bread

Adding koji to your bread starter has been gaining popularity in Japan. Koji can help break down the fibers and starch in the flour, allowing the yeast to work more efficiently.

Recipe idea:
Add a small amount of ground koji rice to your bread dough. This can help enhance the flavor and texture of the bread, giving it a subtle sweetness and improved rise.

Tea Koji

Koji is now being used to speed up the fermentation of tea leaves. Koji-fermented tea breaks down catechins, reducing bitterness and adding a slightly sweet, umami flavor. Recent studies show that koji-fermented tea leaves also have more beneficial amino acids than regular tea.

Seaweed Koji

Seaweed is a staple in the Japanese diet, rich in nutrients and active elements. However, its thick cell wall makes it hard to digest and absorb these benefits effectively.

Innovative chefs now add koji spores to dried seaweed. Koji helps break down the tough cell walls and creates additional beneficial compounds like amylases, protease, and amino acids not naturally found in seaweed. They mix this fermented seaweed with soy sauce to create a flavorful, umami-rich sauce with more depth than regular soy sauce.

Koji Egg

Eggs are highly nutritious and rich in protein, but cooking them breaks down many beneficial compounds. Recently, Japanese chefs and food scientists have started using koji to ferment eggs.

Kewpie, the makers of Japanese mayo, have recently started experimenting with fermenting raw eggs using koji. They discovered that koji-fermented eggs have enhanced flavor and more nutrients compared to regular eggs.

Recipe Idea:
You can ferment eggs by taking boiled or half-boiled eggs and marinating them with shio (salt) koji for 24 hours at room temperature. The egg shouldn’t smell sour but should have a pleasant, sweet, roasted aroma.

Kewpie Koji Egg

Koji Cheese

Using koji to age cheese is an emerging trend in Japan. Some chefs marinate cheese with ground koji to further ripen and ferment the surface, enhancing its umami flavor.

Others incorporate koji at the start of cheese-making to break down dairy proteins. This method speeds up fermentation by up to 70% and boosts the cheese's umami.

Recipe Idea:
Mix any soft cheese (we tried ricotta) with ground koji rice in a 1:1 ratio. Add 5-8% salt by weight and mix well. Put the mixture in a ziploc bag and push out all the air (or vacuum seal). Leave the mixture out at room temperature for 6-12 hours and then store it in the fridge for up to 2 weeks. The koji will have imparted a sweet, umami-packed flavor to the cheese that you wouldn’t get otherwise.

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Using Koji for Skincare, Beauty, and Health

using koji for skincare

Koji has over 100 skin-loving compounds!

Fermenting with Koji produces over 100 super compounds that are amazing for your skin and general health.

That’s why Sake (aka Japanese rice wine) has been considered a natural “fountain of youth” in Japan for centuries and why “fermented rice water” (a marketing mislabel for Japanese rice wine) has recently become a global skincare trend.

You can read about all of the amazing benefits of Sake’s “fermented rice water” here:: Ultimate Guide to Rice Water Skincare

How to Make Sake Kasu (Fermented Rice) Face Mask

Uncover the remarkable benefits of Sake Kasu, packed with amino acids, vitamins, and antioxidants, and learn how to craft a luxurious face mask that rivals the effectiveness of high-end skincare brands like SKII, all at a fraction of the cost.

👉 How to Make Your Own Sake Kasu Face Mask

Sake kasu fermented rice face mask from Made With Ine

Fermented Rice Water Toner

You can create fermented rice water using Koji, strain the liquid using a fine sieve, and then bottle up the liquid in a spray bottle to get natural Koji fermented rice face toner. Just make sure to follow our step-by-step guide below to make it the correct way and then store the toner in the fridge and use it within 2 weeks.

👉 Make Your Fermented Rice Water Without It Spoiling

fermented rice water toner from made with ine

Soap Made With Koji & Sake Kasu

Fermented rice is a gentle and hypo-allergenic ingredient that has been proven to both be gentle on the skin and nourish the skin. Soap made with fermented rice, has been taking off in Japan because of this and has been recommended to even those with sensitive skin and suffering from eczema.

👉 What's To Look For When Buying Soap

fermented rice soap made with ine

INÉ Skin Nutrient Bar: Your Key to Unlocking the Ageless Beauty of Fermented Rice Water!

Introducing the INÉ Skin Nutrient Bar

An Artisan Soap Bar Made with Japanese Sake

Immerse yourself in the transformative power of fermented rice with the Skin Nutrient Bar, meticulously crafted with 100% organic Sake Kasu, a legendary secret from ancient Japanese skincare rituals.

Each bar, lovingly crafted to preserve the full, potent benefits of Sake Kasu, is designed to cleanse, nourish, and rejuvenate your skin from head to toe—all in the meditative mist of your shower. Just as the Toji's hands glow from daily immersion in sake, your skin too can embrace the radiant benefits of sake.

  • Free from Harmful Additives
  • Vegan Friendly 
  • Non-Comedogenic
  • Safe For All Skin Types
  • No Artificial Coloring or Fragrance
Learn More

Unlocking the Power of Koji Mold

ultimate rice based skincare guide

Koji mold is more than just a cornerstone of traditional Japanese cuisine; it's a versatile and powerful agent of fermentation with vast potential across various markets.

So as you can see, Koji mold isn’t just a cornerstone of traditional Japanese cuisine; it’s a powerhouse of fermentation with endless possibilities. From its ancient roots in sake brewing to its modern-day applications in skincare and culinary innovation, Koji keeps proving its amazing versatility and benefits.

Whether it’s boosting the flavors and nutritional value of your food or giving you healthier, more radiant skin, Koji mold shows just how important fermentation is in our lives.

Embrace the magic of Koji and see how this incredible mold can upgrade both your cooking and skincare routines!

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