- Protein turbidity (cloudiness)
This is one of the reasons for cloudiness in seishu. Although somewhat similar in appearance to that caused by hi-ochi kin, the degree of turbidity is lighter, and the fact that the sake clears when heated, only to become cloudy again after cooling, distinguishes it. It is not related to bacteria, but the precipitation of enzyme proteins in the sake.
Even after nama-zake has been clarified by filtration, protein turbidity may occur to some degree after it has been pasteurized and cooled. In extreme cases, sediment may even settle. Although this has no effect on sake flavour, it decreases the commercial value.
The standard procedure for preventing protein turbidity is to carry out ori-sage in order to settle the particles causing cloudiness, then to filter the clear upper part before bottling. The responsible particles are roughly 30% saccharides (galactose and mannose), and 60% crude protein, with metal salts and phenolic substances present in small quantities.