UF milk is a fluid ingredient that contains lower levels of lactose and higher levels of protein than regular milk. During the UF process, milk is passed through a membrane that separates the components by size. The larger milk proteins and milkfat become the retentate stream, or UF milk, while the water, lactose and milk minerals become the permeate stream. The dry version of this product is called milk protein concentrate.
An additional process called diafiltration results in additional carbohydrate removal. Diafiltration involves adding water to the retentate as it is being ultrafiltered to reduce product viscosity and remove even more lactose and minerals.