Film-forming yeast
Japanese: 産膜酵母
A general term for yeasts that form a white film on liquid surfaces. They may appear on the surface of miso or nuka beds, affecting flavor but usually not harmful.
A white film sometimes forms on the surface of miso or nuka beds. This is the work of film-forming yeast. They proliferate on liquid surfaces exposed to air, creating a thin, membrane-like colony.
The sight may be alarming, but in most cases they are harmless. However, excessive growth can produce off-odors like ethyl acetate, reminiscent of paint thinner, so it is common practice to remove them when spotted.
The appearance of film-forming yeast is evidence that the surface is exposed to air. Proper sealing with plastic wrap or a drop lid can prevent their growth.