Manufacturing of the ultra pure water such as: electrical resistance 18MΩ•cm, particulates (>0.2μm) 20 or less, viable bacteria 0.2/mL or less has been made possible by the advent of new technologies such as reverse osmosis, ultrafiltration, electro dialysis, and ion exchange method, along the traditional filtering systems.

[Fig.1] below shows the filtering particle diameter limits of various filter methods.

Filtering with wire mesh and filter cloth have been in traditional use for Sake and soy sauce. This method applies a pressure on the liquid contacting the membrane to cause a pressure difference on each side of the membrane to cause a separation between the material able/unable to pass through the membrane, and is called "Filtering". The membrane used is called "Filter material". The filtering limits of this method using filter cloth is approx. 10μm of solids. The advent of micro-filters using ultra fine fiber material has enabled filtering to 0.1μm.

By using further fine filtering grids such as Cellophane membrane, it became possible to separate colloids. This type of separation method is able to filter bacteria, proteins and colloids, smaller than the normal particles and is called Ultrafiltration method.

With the immergence of semi-permeable lifelike membrane and reverse osmosis methods, high molecular particles and ions are able to be seprated.

[Fig.2] shows the principle of Ultrafiltration
Small sized molecules such as water can pass the membrane, but the larger ones such as colloids and proteins cannot.