ultrafiltration, a form of cross-flow filtration which can be used for alcohol reduction and, more controversially, for tannin removal or concentration. It is looser than reverse osmosis but tighter than sterile filtration. It can also be used to separate colloids from their solution. It is used as an alternative to fining. Proponents suggest it is useful for removal of browning and for reducing tannins in press wines but it is subject to strict regulation and is not permitted in the eu.