Cross-Flow Microfiltration (CFM) is a physical process used to produce protein powder starting from an aqueous solution containing the proteins together with other solutes. An example could be milk serum.
The purification process consists in the passage of the serum through an apparatus containing, parallel to the flow of the fluid to be filtered, a series of ceramic filtration membranes equipped with microscopic holes. The fats and sugars (lactose) pass through these holes, and are therefore eliminated, but it does not let pass proteins larger in size, which are then retained and concentrated. This method is among the most expensive ones used for protein isolation, but it guarantees the highest quality. It can obtain a protein isolate greater than 90% pure, with fat and carbohydrate percentages even below 1%. It is also a purely physical process that does not use any chemical reagents or high temperatures, thus preserving the structural integrity of the obtained proteins and bioactive protein fractions that determine the quality of the protein itself.