The most relevant operation for enzyme concentration is Ultrafiltration. Ultrafiltration is a membrane filtration operation, where pressure difference across the membrane is the driving force. Molecules are separated on the basis of their size in the range from 1,000 to 100,000 Da, so covering most of the enzymes. Despite its potential of fractionation, Ultrafiltration has been mainly used to concentrate enzymes by removing solvent and smaller size solutes.