Koji(Aspergillus oryzae) is often called moyashi(bean sprouts) in the sake industry, because of its appearance when viewed under a microscope. Koji was named by Herman Ahlburg in 1876, who was a professor of medicine in Tokyo at the time.
Oryzae refers to the rice plant, Oryzae sativa, (cultivated / domesticated rice) so the close relationship between koji and rice is clear.
In Asian countries, alcoholic beverages are commonly produced using koji . The koji fungi are divided into two types: mochi koji and bara koji. Mochi koji which is normally propagated when dry, powdered rice, and other crops are mixed with water. It is called mochi koji because the raw materials look like a block of sticky rice, called mochi in Japanese.
On the other hand, bara koji can propagate on steamed crops. As a prefix, bara means “separated “in Japanese. The fungus propagates on each single rice grain, so it is called bara koji.
Unlike mochi koji,bara koji can dissolve thermal denaturated protein. Since koji fungus, in general, propagates by consuming amino acids (they can not eat protein), an additional process to convert protein to amino acid is needed. But mochi koji cannot dissolve the thermal denaturated protein of steamed rice, so they can not survive on the steamed rice.
Bara koji is a rare koji(Normally mochi koji is used in the other Asian countries)which brings to sake an unexampled production process which makes Japanese sake one of the unique alcoholic beverages in the world.
The pictures of Aspergillus Oryzae are provided by Akitakonnoshoten