Koji
(cooked cereals or legumes inoculated with Aspergillus oryzae – fermentation starter and food ingredient)

Description

• In practical terms, koji refers to rice, cereals (barley, wheat) or legumes (soybeans) that have been cooked and inoculated with the filamentous fungus Aspergillus oryzae, then incubated under controlled humidity and temperature until the substrate is covered by fungal mycelium.

• It is the traditional starter for many Japanese (and broader East Asian) fermentations: miso, soy sauce, sake, mirin, amazake, rice vinegar, shio-koji, modern garums and other umami-rich condiments.

• Commercially, koji is available as fresh or dried rice koji, often in the form of whole grains, broken grains, granules or pastes (e.g. shio-koji), for home, craft or industrial use.

• Its primary role is to provide very high enzymatic activity (amylases, glucoamylases, proteases, peptidases, lipases, etc.), capable of breaking down starch, proteins and lipids in the substrate and releasing sugars, peptides and amino acids (including glutamate) that generate sweetness and umami in fermented products.

Indicative nutritional values (per 100 g dried rice koji)

(Typical ranges from commercial dried rice-koji products; values vary with rice variety, drying level and process.)

• Energy: ≈ 300–380 kcal

• Water: ≈ 5–12 g

• Protein: ≈ 6–9 g

• Total fat: ≈ 0.5–2 g

  • first occurrence: SFA/MUFA/PUFA = saturated / monounsaturated / polyunsaturated fatty acids.
    The lipid fraction is small and not the nutritional focus, but, as in rice, the profile is dominated by unsaturated fats (mainly MUFA/PUFA) with a modest SFA share, without particular concern when consumed at typical intakes.

• Total carbohydrates: ≈ 70–85 g

  • of which sugars: ≈ 10–20 g (increase with starch breakdown by amylases)

• Fibre: ≈ 1–3 g (depending on rice/cereal refinement)

• Sodium: very low in plain rice koji; very high in salty derivatives such as shio-koji (koji + salt).

• Micronutrients (indicative):

  • B-group vitamins (e.g. B1, B2, niacin) from the grain and fungal metabolism,

  • small amounts of minerals (phosphorus, magnesium, potassium, iron), especially when using wholegrain substrates.

Key constituents

• Substrate components

  • Starch and dextrins from rice/cereals, partially hydrolysed into maltodextrins and sugars (glucose, maltose).

  • Vegetable proteins from rice/barley/soy, partly hydrolysed to peptides and free amino acids (glutamate, aspartate, alanine, etc.).

  • A minimal but present lipid fraction, generally with more unsaturated than saturated fatty acids.

• Metabolites and enzymes from Aspergillus oryzae

  • Amylases and glucoamylases: convert starch to fermentable sugars, increasing sweetness and creating substrate for yeasts and lactic bacteria.

  • Proteases and peptidases: release peptides and amino acids, enhancing umami and improving protein digestibility.

  • Lipases and other hydrolases: liberate fatty acids and modify lipids and aroma precursors.

  • Trace production of vitamins and cofactors which may slightly enrich the micronutrient profile of the substrate.

• Pigments and aroma precursors

  • Fungal pigments (e.g. in yellow/white/black koji types) that lightly influence colour.

  • A complex pool of precursors that, during further fermentation and/or cooking (miso, soy sauce, sake, garums), yield aldehydes, organic acids, esters and Maillard-derived aromas.

Production process

(Generic scheme for rice koji; other grains/legumes follow similar steps with adjustments.)

• Substrate preparation

  • Selection of grain/legume (polished rice, barley, wheat, soybeans, etc.).

  • Washing and soaking to hydrate the kernels.

  • Steaming/boiling to gelatinise starch and open the structure to enzymatic attack.

• Inoculation with spores (tane-koji)

  • Cooling of the cooked substrate to a controlled temperature.

  • Inoculation with spores of Aspergillus oryzae (tane-koji / commercial koji starter), distributed evenly over the grains.

• Incubation in a controlled environment (koji muro)

  • Spreading the inoculated grains in shallow layers; careful control of aeration, high humidity and temperature (~28–32 °C).

  • Over 2–3 days the mycelium grows through the grains, forming a white, velvety mat; the koji maker regularly turns and redistributes the grains to prevent overheating and optimise enzyme production.

• Harvest and stabilisation

  • Fresh koji is used immediately as a fermentation starter (for miso, shoyu, sake, etc.).

  • For commercial dried koji, the grains are dried to a safe moisture content, sometimes broken or milled, then packaged.

  • Packaging: sealed bags or containers, protected from moisture and light to preserve enzyme activity and microbiological stability.

Physical properties

• Appearance: grains of rice/cereal covered with white mycelium, sometimes with slight yellow–green shades; dried koji appears as dry, light, often brittle grains.

• Odour: typically sweet, gently fungal and malty, reminiscent of cooked rice, nuts and occasionally sake.

• Texture:

  • fresh koji: moist, soft but grain-separated;

  • dried koji: hard/brittle; in liquids (brines, shio-koji) it forms semi-thick suspensions or pastes.

• Water activity: high in fresh koji (highly perishable); reduced to safe levels in dried koji.

Sensory and technological properties

• Sensory profile

  • Development of sweetness via conversion of starch to sugars.

  • Enhancement of umami and complexity in fermented foods through peptides, amino acids (notably glutamate) and fermentation-derived aromas.

• Technological functions

  • Saccharifying power: converts starch into fermentable sugars, essential for sake, amazake, shio-koji and various grain ferments.

  • Proteolytic power: pre-digests proteins in soy/cereals (miso, soy sauce, shio-koji), making them more accessible to bacteria and yeasts and generating savoury peptides.

  • Tenderising effect: in marinades (especially shio-koji), proteases soften meat and fish and improve juiciness and perceived succulence.

  • Colour and flavour development: by increasing reducing sugars and free amino acids, koji sets the stage for Maillard reactions during cooking and long maturation (miso, garums, sauces), producing deep colour and roasted/caramelised notes.

Food applications

• Home and craft use

  • Preparation of miso, soy sauce, tamari, amazake, shio-koji, rice vinegar-type condiments and other fermented sauces.

  • Marinades for meat, fish and vegetables using shio-koji to enhance tenderness and umami.

  • Experimental use in bread and baked goods to add malty notes and partial pre-digestion of starch.

• Food industry

  • Starter for controlled solid-state fermentation (SSF) on cereals, legumes and by-products to produce seasonings, flavour enhancers and umami concentrates.

  • Component of sauces, liquid condiments, fermented pastes, speciality vinegars.

  • Innovative applications on non-traditional substrates (Western legumes, pseudo-cereals, vegetable trimmings) to create upcycled, high-value ingredients.

Nutrition & health

• Koji itself (especially dried rice koji) is an energy-dense carbohydrate ingredient, but it is typically used in small amounts as a starter or seasoning rather than in large portions.

• Direct nutritional contributions:

  • Carbohydrates partly pre-hydrolysed to sugars → easy fermentability and “quick energy”.

  • Partially hydrolysed proteins → peptides and free amino acids that are generally more digestible and contribute to flavour.

  • Modest contribution of vitamins and minerals depending on the substrate.

• The more significant impact of koji is indirect, via the foods it helps create:

  • increased palatability and diversity of flavours in fermented foods (miso, soy sauce, amazake, sake, etc.);

  • modification of protein structure, often towards forms that are easier to digest (though not necessarily non-allergenic);

  • generation of bioactive compounds (peptides, organic acids) in some matrices.

Portion note:

• As a starter or seasoning in home use: typically 5–20 g of rice koji or shio-koji in marinades or small dishes.

• Larger amounts (tens of grams) are used in making miso, soy sauce, sake and similar products, but the final portion of koji per serving of finished food is usually modest.

Allergens and intolerances

• Koji inherits the allergens of the substrate:

  • gluten when made on wheat/barley,

  • soy when made on soybeans,

  • any other inherent allergen of the base grain/legume.

• Aspergillus oryzae is considered a food-grade, non-toxigenic fungus with a long history of safe use; however:

  • occupational exposure to large amounts of spores (sake breweries, koji factories) has been associated with rare cases of respiratory sensitisation;

  • for consumers, the allergenic risk directly linked to A. oryzae itself is considered very low, but not absolutely zero in highly sensitised individuals.

• Fermentation may reduce but not necessarily eliminate the allergenicity of proteins such as those from soy or wheat; people with strong allergies to these foods should evaluate koji-derived products with their allergist’s guidance and follow labelling carefully.

Quality & specification (typical topics)

• Composition

  • Moisture (critical for microbiological stability of dried koji), ash, protein, carbohydrate, salt (especially in shio-koji).

  • Enzymatic activity: units of amylase, glucoamylase, protease per gram, often key for industrial users.

• Microbiological parameters

  • Dominance of Aspergillus oryzae on the substrate.

  • Absence of unwanted toxigenic molds (e.g. A. flavus, A. parasiticus) and bacterial pathogens.

• Sensory parameters

  • Aroma: sweet, malty, lightly fungal without musty, damp, earthy or rancid off-notes.

  • Visual: uniform mycelial growth, no irregular dark or bright-coloured patches.

Storage & shelf-life

• Fresh koji

  • Highly perishable; must be kept refrigerated and used within a few days.

• Dried koji

  • Store in a cool, dry place away from light, in well-sealed packaging.

  • Typical shelf-life: several months up to ~12 months, depending on moisture and storage conditions.

• Koji pastes and brines (e.g. shio-koji)

  • High salt and/or acidity → good microbiological stability.

  • Usually stored refrigerated after opening; can remain usable for months, though enzymatic activity and flavour continue to evolve.

Safety & regulatory

• In countries where it is traditionally used, koji and Aspergillus oryzae have a long history of safe use, and A. oryzae is recognised as a food-grade/GRAS or QPS-like organism when coming from non-toxigenic, well-characterised strains.

• Facilities should operate under GMP/HACCP systems, with control over:

  • purity and identity of the A. oryzae strain;

  • fermentation parameters (temperature, humidity, aeration) to prevent growth of undesirable microbes;

  • contaminant loads in the substrate (heavy metals, pesticides, pre-existing mycotoxins).

Labelling

• In ingredient lists, koji-related items may appear as:

  • “rice (or other grain) fermented with Aspergillus oryzae”, “rice koji”, “barley koji”, “shio-koji”, etc., often keeping the term “koji” untranslated.

• Labelling must clearly indicate:

  • substrate allergens (e.g. wheat, barley, soy) where applicable;

  • any origin claims (e.g. specific rice types, non-GMO, organic);

  • for professional/industrial products, enzyme-activity specifications may be included.

Troubleshooting

• Musty, “wet mold” or rotten smell

  • Likely cause: contamination by undesirable microflora, excessive humidity, poor aeration.

  • Action: discard batch; review humidity control, ventilation and hygiene.

• Abnormal colour (black, dark green, irregular patches)

  • Likely cause: growth of non-target molds, potentially toxigenic.

  • Action: discard product; verify starter purity and environmental controls.

• Low enzymatic activity

  • Likely cause: suboptimal temperature/humidity, substrate too dry or too wet, over/under-incubation.

  • Action: optimise fermentation conditions (time, temperature, humidity, ventilation) and spore dosage.

• Dried koji clumping or condensation in packages

  • Likely cause: moisture uptake during storage.

  • Action: check packaging integrity, improve moisture control and storage conditions; consider batch at risk of microbial or sensory degradation.

Sustainability & supply chain

• Koji is a tool for value-adding to cereals, legumes and by-products:

  • it transforms simple raw materials (including lower-grade fractions and some side streams) into highly flavoured, functionally rich condiments and ingredients;

  • supports development of local, small-scale fermentation businesses and innovative “upcycling” of food resources.

• Koji production generates organic-rich effluents and solid by-products; these require suitable management, and BOD/COD levels in wastewater must be addressed with appropriate treatment systems.

• Used on local substrates with attention to energy, water and waste, koji-based fermentation can be part of low-waste, high-value production models in both craft and industrial settings.

Main INCI functions (cosmetics)

• In cosmetic and nutricosmetic contexts, koji-related ingredients may appear with names such as Rice Ferment Filtrate, Rice Ferment (Sake) Filtrate, or combinations with yeasts/fungi.

• Typical functions:

  • conditioning and moisturising agents for skin and hair,

  • sources of amino acids, peptides, organic acids and fermentation metabolites that may support claims on skin texture, radiance or barrier support.

• These ingredients follow cosmetic, not food, regulations and must meet strict microbiological and toxicological purity standards.

Conclusion

Koji is less a food eaten in its own right and more a microbial–enzymatic tool that underpins a wide range of traditional and modern fermented foods. By colonising cooked grains and legumes with Aspergillus oryzae, it generates a highly active enzymatic system that converts starch, proteins and lipids into sugars, peptides and free amino acids, driving sweetness, umami and complex aromatics. While its direct nutritional impact is modest at typical use levels, its role in creating more digestible, flavourful and functionally rich fermented products is central. When produced with safe A. oryzae strains under robust GMP/HACCP, with clear allergen labelling and thoughtful use of local substrates and resources, koji becomes a strategic ingredient and process tool for both artisanal and industrial fermentation.

Mini-glossary

• SFA/MUFA/PUFA – saturated / monounsaturated / polyunsaturated fatty acids; main structural categories of fatty acids in fats and oils. In koji, the overall fat level is low, with a pattern similar to the underlying grain (more unsaturated than saturated), and therefore not a critical health concern in normal use.

• VB (biological value) – measure of protein quality in terms of how efficiently the body can use it for tissue protein synthesis; in koji the VB is mainly determined by grain/legume proteins, with digestibility modestly enhanced by enzymatic hydrolysis.

• SSF – solid-state fermentation; fermentation carried out on moist solids with little free water (e.g. grains colonised by fungi), the typical format for koji production.

• GMP/HACCP – good manufacturing practices / hazard analysis and critical control points; structured systems for ensuring hygienic, controlled production and hazard management (microbial, chemical, physical) in koji plants and downstream fermentations.

• BOD/COD – biochemical oxygen demand / chemical oxygen demand; indicators of organic and oxidisable load in wastewater from washing, cooking and cleaning, used to design and monitor treatment plants associated with fermentation facilities.

References__________________________________________________________________________

Dai H, Hariwitonang J, Fujiyama N, Moriguchi C, Hirano Y, Ebara F, Inaba S, Kondo F, Kitagaki H. A Decrease in the Hardness of Feces with Added Glucosylceramide Extracted from Koji In Vitro-A Working Hypothesis of Health Benefits of Dietary Glucosylceramide. Life (Basel). 2024 Jun 7;14(6):739. doi: 10.3390/life14060739. 

Abstract. Skin barrier function, prevent colon cancer, head and neck cancer, and decrease liver cholesterol. However, the mechanism of action has not yet been elucidated. In this study, we propose a new working hypothesis regarding the health benefits and functions of glucosylceramide: decreased fecal hardness. This hypothesis was verified using an in vitro hardness test. The hardness of feces supplemented with glucosylceramide was significantly lower than that of the control. Based on these results, a new working hypothesis of dietary glucosylceramide was conceived: glucosylceramide passes through the small intestine, interacts with intestinal bacteria, increases the tolerance of these bacteria toward secondary bile acids, and decreases the hardness of feces, and these factors synergistically result in in vivo effects. This hypothesis forms the basis for further studies on the health benefits and functions of dietary glucosylceramides.

Kosakai T, Kato H, Sho C, Kawano K, Iwai K, Takase Y, Ogawa K, Nishiyama K, Yamasaki M. 2019. Dietary fermented products using koji mold and sweet potato-shochu distillery by-product promotes hepatic and serum cholesterol levels and modulates gut microbiota in mice fed a high-cholesterol diet. PeerJ 7:e7671 

Abstract. It has been reported that fermented products (FPs) prepared from sweet potato-shochu distillery by-product suppressed weight gain and decreased serum cholesterol levels in mice under normal dietary conditions. Furthermore, from the information gained from the above data regarding health benefits of the FPs, the aim of this study was evaluating the effects of dietary FPs on lipid accumulation and gut microbiota in mice with or without cholesterol-load in the diet. C57BL/6N mice were fed normal (CO) diet, CO with 10% FPs (CO + FPs) diet, cholesterol loaded (HC) diet, or HC with 10% FPs (HC + FPs) diet for 8 weeks. The mice were then euthanized, and blood samples, tissue samples, and feces were collected. The adipose tissue weight and liver triglyceride levels in the HC + FPs diet groups were significantly reduced compared to that in the HC diet groups. However, FPs significantly increased the serum non-high-density lipoprotein cholesterol (HDL-C) levels, the ratio of non-HDL-C to HDL-C and hepatic total cholesterol levels in mice fed cholesterol-loaded diet compared with that of the HC diet group. Since dietary FPs significantly decreased the protein expression levels of cholesterol 7 alpha-hydroxylase 1 in the HC + FPs diet groups, the cholesterol accumulation in FPs group may be explained by insufficient catabolism from cholesterol to bile acid. In addition, the dietary FPs tended to increase Clostridium cluster IV and XIVa, which are butyrate-producing bacteria. Related to the result, n-butyrate was significantly increased in the CO + FPs and the HC + FPs diet groups compared to their respective control groups. These findings suggested that dietary FPs modulated the lipid pool and gut microbiota.

Allwood, J. G., Wakeling, L. T., & Bean, D. C. (2021). Fermentation and the microbial community of Japanese koji and miso: A review. Journal of Food Science, 86(6), 2194-2207.

Abstract. Miso is a well-known traditional Japanese fermented food, with a characteristic savory flavor and aroma, known predominately as the seasoning in miso soup. Miso production involves a two-stage fermentation, where first a mold, such as Aspergillus oryzae, is inoculated onto a substrate to make koji. A subsequent fermentation, this time by bacteria and yeast, occurs when the koji is added to a salt and soybean mash, with the miso left to ferment for up to 2 years. The microbial community of miso is considered essential to the development of the unique taste, texture, and nutritional profile of miso. Despite the importance of microorganisms in the production of miso, very little research has been undertaken to characterize and describe the microbial process. In this review, we provide an overview of the two-stage fermentation process, describe what is currently known about the microbial communities involved and consider any potential health benefits associated with the consumption of miso, along with food safety concerns. As the popularity of miso continues to expand globally and is produced under new environmental conditions, understanding the microbiological processes involved will assist to ensure that global production of miso is safe as well as delicious.

Hamajima, H., Matsunaga, H., Fujikawa, A., Sato, T., Mitsutake, S., Yanagita, T., ... & Kitagaki, H. (2016). Japanese traditional dietary fungus koji Aspergillus oryzae functions as a prebiotic for Blautia coccoides through glycosylceramide: Japanese dietary fungus koji is a new prebiotic. Springerplus, 5(1), 1321.

Abstract. Background. The Japanese traditional cuisine, Washoku, considered to be responsible for increased longevity among the Japanese, comprises various foods fermented with the non-pathogenic fungus Aspergillus oryzae (koji). We have recently revealed that koji contains an abundant amount of glycosylceramide. Intestinal microbes have significant effect on health. However, the effects of koji glycosylceramide on intestinal microbes have not been studied. Materials and methods Glycosylceramide was extracted and purified from koji. C57BL/6N mice were fed a diet containing 1 % purified koji glycosylceramide for 1 week. Nutritional parameters and faecal lipid constituents were analyzed. The intestinal microbial flora of mice on this diet was investigated. Results Ingested koji glycosylceramide was neither digested by intestinal enzymes nor was it detected in the faeces, suggesting that koji glycosylceramide was digested by the intestinal microbial flora. Intestinal microbial flora that digested koji glycosylceramide had an increased ratio of Blautia coccoides. Stimulation of B. coccoides growth by pure koji glycosylceramide was confirmed in vitro. Conclusions. Koji functions as a prebiotic for B. coccoides through glycosylceramide. Since there are many reports of the effects of B. coccoides on health, an increase in intestinal B. coccoides by koji glycosylceramide might be the connection between Japanese cuisine, intestinal microbial flora, and longevity.

Yoshizaki, Yumiko, et al. Rice koji reduced body weight gain, fat accumulation, and blood glucose level in high-fat diet-induced obese mice. PeerJ 2 (2014): e540.

Abstract. Rice koji is considered a readily accessible functional food that may have health-promoting effects. We investigated whether white, yellow, and red koji have the anti-obesity effect in C57BL/6J mice fed a high-fat diet (HFD), which is a model for obesity. Mice were fed HFD containing 10% (w/w) of rice koji powder or steamed rice for 4 weeks. Weight gain, epididymal white adipose tissue, and total adipose tissue weight were significantly lower in all rice koji groups than in the HFD-rice group after 4 weeks. Feed efficiency was significantly reduced in the yellow koji group. Blood glucose levels were significantly lower in the white and red koji groups with HOMA-R and leptin levels being reduced in the white koji group. White and red koji increased glucose uptake and GLUT4 protein expression in L6 myotube cells. These results showed that all rice koji have the anti-obesity or anti-diabetes effects although the mechanisms may differ depending on the type of rice koji consumed.

Giri, A., Osako, K., Okamoto, A., Okazaki, E., & Ohshima, T. (2012). Effects of koji fermented phenolic compounds on the oxidative stability of fish Miso. Journal of food science, 77(2), C228-C235.

Abstract. In the present study, Aspergillus oryzae-inoculated koji inhibited lipid oxidation in fermented fish paste rich in polyunsaturated fatty acids following a long fermentation period. The fermentation of koji by A. oryzae liberated several bioactive phenolic compounds, including kojic acid and ferulic acid, which were the most abundant. A linear correlation between several phenolic compounds and their bioactive properties, including their radical-scavenging activity, reducing power, metal-chelating activity, and ability to inhibit linoleic acid oxidation was observed. This suggested an important role of koji phenolics in the oxidative stability of fermented fish paste. The activities of different carbohydrate-cleaving enzymes, including α-amylase, cellulase, and β-glucosidase, were positively correlated with the liberation of several phenolic compounds through koji fermentation. Thus, the application of koji offers a novel strategy to enhance the oxidative stability of newly developed fermented fish miso.

Sugihara, Y., Ikushima, S., Miyake, M., Kirisako, T., Yada, Y., & Fujiwara, D. (2018). Improvement of skin conditions by ingestion of Aspergillus kawachii (Koji) extract containing 14-dehydroergosterol in a randomized, double-blind, controlled trial. Clinical, Cosmetic and Investigational Dermatology, 115-124.

Abstract. Purpose. The present study examined the effect of ingestion of Koji extract containing 14-dehydroergosterol (14-DHE), prepared from Aspergillus kawachii NBRC4308, on improvement of skin conditions among healthy volunteers. Subjects and methods In a randomized, double-blind, placebo-controlled, parallel-group study, 70 healthy adult women who felt that their skin was dry ingested either a placebo dietary supplement or Koji extract (200 mg/day) supplement containing 0.1% 14-DHE for 12 weeks. Throughout the treatment period and for 4 weeks afterward, objective indicators – including moisture content of the stratum corneum, trans-epidermal water loss (TEWL), and skin wrinkles – were evaluated; in addition, the subjects answered a questionnaire on their skin conditions with ratings on a visual analog scale. Statistical analysis was conducted on the basis of differences from baseline scores. Results Compared with the placebo group, the Koji extract group showed significantly increased forearm moisture at 4, 8, and 16 weeks (p < 0.05 on unpaired t-test). The questionnaire survey showed a marked improvement in skin conditions, particularly crow’s feet, in the Koji extract group versus the placebo group at 8 weeks (p < 0.05 by unpaired t-test). Furthermore, the Koji extract group showed a trend (p < 0.10) toward improvement in skin moisture (at 4 weeks), dryness around the eyes/mouth (at 4 weeks), and overall skin condition (at 8 weeks) versus the placebo group. Conclusion. Ingestion of Koji extract containing 14-DHE was demonstrated to have positive effects toward improving skin conditions – in particular, on increasing skin moisture in the stratum corneum.