Ultrafiltration is the coarsest of the membrane technologies, generally being limited to removing colloids the size of viruses and molecules the size of large proteins and “color bodies” derived from rotting vegetation. Ultrafilters are produced as long sheets of membrane that are rolled up into a cylinder. Alternating layers of netting provide space for water to penetrate into the interior of the roll. This provides more surface area than the pleats often used for microfilters. They require good prefiltration by a micro-filter or fine-filter because they clog quickly. Therefore, they do not find much use in water treatment. Some food processing applications provide a “waste” stream that recirculates. This helps delay clogging and enhances the life of the membrane.