Microfiltration (seimitsu-roka) is filtration carried out at a pore size of between 0.2 – 3μm. The pore size is larger than for ultrafiltration, but it allows for accurate and efficient removal of colloidal particles in the liquid, which cannot be removed by filtration through paper or such. At less than 0.5µm, not only blood and yeast cells, but also hi-ochi (lactic acid) and other bacteria cannot pass through, so it is said that this method allows the removal of micro-organisms without removing flavour. It is used not only for filtering nama-zake in storage, but to filter mashing water (shikomi-sui) and water used in dilution wari-mizu (割水).
The SF Filter, a recently-developed hollow-fibre filter, has specifications between ultrafiltration and microfiltration.