Koji mold, miso making and health findings
What it found
Miso is a fermented soybean paste made using koji mold, and a large Japanese study found that people who ate more fermented soybean products were less likely to die during the study period.
Most other health research on miso has been in cells or animals, not people.
What they found
Studies in people
Miso and blood pressure
Two published studies of rice miso found that long-term standard consumption of miso soup did not affect blood pressure in human subjects. A study of 25,738 Japanese men and women found that portion size of soy sauce or miso was not associated with hypertension.
Fermented soy and death risk
A cohort study followed 92,915 men and women aged 45 to 74 from 1995-1998 to 2012. The risk of death decreased with increasing consumption of fermented soybean products in both men and women, but no association was found for all types of soybean products combined.
Animal and lab studies
Safety of koji mold
Koji mold has been used in Japanese food fermentation for over a thousand years. Government, university, and manufacturer research in the 1970s found that none of the starter koji strains produced aflatoxins, and later molecular studies confirmed deletions or dysfunction in the aflatoxin biosynthesis genes.
Other findings
Miso varieties and uses
Miso is a semisolid paste made from soybeans fermented with koji mold and salt. It comes in rice, barley, soybean, and mixed types, and is most commonly eaten as miso soup.
Koji making process
Koji making is the most critical step in miso production. Rice koji takes 42 to 48 hours to produce, with temperatures maintained at 28 to 32 degrees Celsius during loading and 40 degrees Celsius or below during fermentation.
Enzymes in koji
Koji mold produces amylases that break down starches into glucose and proteases that break down proteins into amino acids and peptides. These enzymes determine the taste, aroma, and digestibility of miso.
What the authors conclude
- They say that miso is an essential part of the Japanese diet and contains a wide variety of nutritious fermentation products derived from soybeans and grains.
- They highly anticipate that the increasing popularity of miso in the world will play a role in facilitating further globalization of Japanese culinary culture.
How it was done
The authors wanted to explain what miso is in Japanese culture and food production, describe the varieties and how it is made, and review scientific research on koji mold species, their safety, and the enzymes they produce during fermentation.
They reviewed the steps of miso making, the types of koji mold used, the enzymes produced, and the microbes involved in fermentation. They also reviewed studies on miso and health, including a cohort study that followed 92,915 men and women aged 45 to 74 for up to 17 years.
What it can’t tell you
- Most health studies on miso have been done in cells or laboratory animals, not in people, so the effects in humans are not well known.
- The cohort study can show a link between fermented soybean product consumption and death risk, but it cannot prove that eating these products caused the lower risk.
Who paid
- Conflicts
- The authors declare no conflict of interest.
- Authors work at
- Food Research Institute, Japan; Tokyo University of Agriculture and Technology, Japan; Central Miso Research Institute, Japan
The paper
- Title
- Japanese Traditional Miso and Koji Making
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Kusumoto KI, Yamagata Y, Tazawa R, et al (2021). Japanese Traditional Miso and Koji Making. Journal of fungi (Basel, Switzerland). doi:10.3390/jof7070579Free full textPubMed 34356958DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error