Koji & Amazake: Nutrients, What Research Shows and Safety

Q: Can koji mold make aflatoxin?

The food-use mold A. oryzae did not make aflatoxin in a rice test, while wild A. flavus did. [3] Wild A. oryzae strains can carry mycotoxin genes, and industrial strains have been bred without them. [4]

Koji is rice grown with the mold Aspergillus oryzae; amazake is the sweet drink made from it. What trials found on bowels and skin, sugar, mold safety and labels.

Content last updated October 24, 2026. This page has not been medically reviewed.

Close-up of koji & amazake: nutrients, what research shows and safety

Koji is steamed rice that has been grown with a mold called Aspergillus oryzae, a mold used for thousands of years in traditional Asian fermented foods and drinks, including sake. [3] [9] Amazake is a thick, sweet Japanese rice drink. There are two kinds: koji amazake, made from rice koji, and sakekasu amazake, made from the solids left over from sake making. [1] People drink it as a traditional sweet drink and for its reputed health benefits. This page keeps the food apart from supplements and hype, and says what the research does and does not show.

Read this first

Evidence in one line: a 2025 review says bowel function and skin trials are the best studied areas for amazake. Most of the rest is animal work or preliminary. [1]
It is sweet: koji turns rice starch into sugar, and glucose is the main sugar in koji amazake. [2] The review says long-term and large-intake tests found few concerns about weight gain or blood sugar. [1] People with diabetes should still check the label and ask their care team.
Mold safety: the food-use mold A. oryzae is a different species from its aflatoxin-producing relative A. flavus. In a rice test, only the wild A. flavus strain made aflatoxin. [3] Wild strains of A. oryzae can carry genes for mycotoxins, and food-industry strains have been bred to lack them. [4]
Alcohol: koji amazake is described as a non-alcoholic drink. [1] [6] We did not read a source giving the alcohol in the sake-lees kind, so read the label if you avoid alcohol.
Allergy: for trouble breathing or swelling of the face or throat after eating, call 911 (or your local emergency number).

What is in it (USDA values)

The USDA data file for this food is empty, and we did not read a peer-reviewed table of calories or nutrients for amazake. So we show no USDA numbers and no % Daily Value. Nutrition varies a lot by recipe: how much water was added, how long the rice was digested by the koji enzymes, and whether sugar or other ingredients were added. Read the label. What the papers say about composition is below.

Component	What the sources say	Source
Main sugar	Glucose is the main component of koji amazake; the starch in rice is broken into sugars by koji enzymes.	[2] [6]
Other carbohydrates	It also contains isomaltose, a sugar that has been linked to gut health in lab and mouse studies.	[2]
Alcohol	Koji amazake is described as non-alcoholic; no figure for sake-lees amazake was read.	[1] [6]
B vitamins, minerals, amino acids	A trial paper says amazakes from rice and koji are rich in B vitamins, minerals, essential amino acids and oligosaccharides. No amounts were given in the text we read.	[5]

Plant and fungal compounds: reviews say the active compounds in amazake that explain its effects are not yet identified. [1] A review of mold-fermented foods notes beta-glucans and chitin as likely drivers of gut effects in mold foods in general, but this is not shown for amazake in people. [7]

What research says

Health goal	What the sources found	Strength of evidence	What was studied
Constipation and bowel movements	The 2025 review says both types of amazake have been well studied for improving bowel movements and may help constipation. [1]	Promising but limited (we read only the abstract; trial size and quality not shown)	Koji amazake and sake-lees amazake, people
Skin	The review says benefits on skin barrier function and skin water content are well established in randomized trials. [1] In one 8-week double-blind trial of 40 adults, a milk amazake (made with milk and koji) improved skin elasticity and lowered water loss through the skin versus baseline; elasticity change was higher than placebo. [5]	Promising but limited	Amazake drinks, healthy adults; the milk version is a different product
Gut bacteria	Effects on gut bacteria were mainly shown in animals. Mice fed a double-saccharified koji amazake had changed gut bacteria. [1] [2]	Lab or animal only	Mice
Blood sugar, weight	The review found few concerns about weight gain or blood sugar with koji amazake in long-term and large-intake tests. [1] It did not show it helps.	Insufficient evidence	Safety tests
Obesity, metabolic syndrome, fatty liver	The review calls the evidence preliminary. [1]	Insufficient evidence	Mostly preliminary studies
Energy, immunity, anti-aging	Proper evidence not found in the sources we read.	No good evidence of benefit found	None

Eaten as food vs taken as a supplement. The trials above used drinks. We did not read a trial of a koji supplement or extract in this review. Koji is also used as a cooking ingredient (see the pages on soy sauce and tamari and gochujang and doenjang). We did not check trial funding in every study; abstracts often do not say.

How much is a normal serving

We did not find an official serving size for amazake (USDA, MyPlate, NHS, EFSA or Japan). That is information, not a prescription. Because koji amazake contains sugar from the rice, treat it as a sweet drink, not as plain water. [2]

Safety, allergy and medicines

Sugar and diabetes: glucose is the main sugar in koji amazake. [2] The 2025 review says safety tests show few concerns about blood sugar. [1] That is not a green light for people with diabetes. Ask a clinician if you use insulin or blood sugar medicines.
Mold species and mycotoxins: A. oryzae is the food-use species (called GRAS in one paper). [3] In a rice test it did not make aflatoxin, while a wild A. flavus strain did. [3] A review of industrial strains says wild-type A. oryzae can have the genes for three mycotoxins (aflatoxins, cyclopiazonic acid and 3-nitropropionic acid) and that a mycotoxin-free lineage has been developed. [4] A 2025 genome study found the line between A. oryzae and A. flavus is blurry, with signs of several separate domestications. [8] Buy koji from a reputable maker.
Occupational exposure: one case report describes a fungal ball in the sinus of a sake brewery worker, caused by A. oryzae from the koji at work. It was rare and she recovered after surgery. [9] This is about breathing koji spores at work, not about drinking amazake.
Alcohol, pregnancy and children: koji amazake is described as non-alcoholic. [1] [6] We did not read official advice on amazake in pregnancy. If you avoid alcohol completely, check that the product is not the sake-lees kind.
Allergy: rice and koji are not among the nine major US allergens. [10] Some amazake is made with milk or other ingredients, so read the label. Call 911 for trouble breathing or swelling of the face, lips or throat.
Rice and arsenic: amazake is made from rice. FDA found no basis to tell adults to change how much rice they eat, and advises a varied diet; infants need more care. [11] See arsenic in rice and rice products.
Medicines: we did not read any source describing a direct interaction between amazake or koji and a medicine.
Kidney disease: we did not read potassium or phosphorus values for amazake.

Choosing, storing and food safety

Check the label for the type (koji or sake-lees), added sugar and alcohol.
Home koji making is a specialist craft, and we did not read official guidance for it. Use a trusted starter and clean equipment, and discard anything with odd colors or smells.
For home fermenting in general, official advice says to use tested recipes and not to cut the salt or change acidity in vegetable ferments. [12]

Fermented foodAspergillus oryzae, Oryza sativa

Health connections for Koji & Amazake

What research links to eating or drinking this food, and how strong the evidence is. Many studies are observational or use juice, powder, oil or extracts rather than the food as eaten; each card says which.

Amazake and constipation or bowel movements

Preliminary or mixed

A 2025 review says both koji amazake and sake-lees amazake have been well studied for bowel movements and may help constipation. We read only the abstract, so trial size and quality are not known.