1970s, but industry perception of shampoo cleaning changed with the advent of encapsulation. Hot-water extraction, also regarded as preferable by all manufacturers, had not been introduced either. Wet shampoos were once formulated from coconut oil soaps; wet shampoo residues can be foamy or sticky, and steam cleaning often reveals dirt unextracted by shampoos. Since no rinse is performed, the powerful residue can continue to collect dirt after cleaning, leading to the misconception that carpet cleaning can lead to the carpet getting "dirtier faster" after the cleaning. The best method is truckmounted hot water extraction. When wet-shampoo chemistry standards converted from coconut oil soaps to synthetic detergents as a base, the shampoos dried to a powder, and loosened dirt would attach to the powder components, requiring vacuuming by the consumer the day after cleaning. Dry foam carpet cleaning Dry foam cleaning involves applying a cleaning foam blanket to the surface area of a carpet immediately after a dry clean. The foam is left to stand for 10 minutes to allow chemical agents to affect the carpet. This method is typically used to remove grease from the surface; some foams have color brighteners, protectants and anti-soiling agents. It is not a completely dry method since the foam is 90% air and 10% liquid. A dry foam machine consists of a pressure tank in which a solution of water and shampoo is added. This method is used for water-sensitive carpets, needle felt, and other carpet types whose construction inhibits sufficient water extraction. Vacuum washing Vacuum washing employs a washhead that sprays water without detergent and immediately removes it by suction, creating a swirl of water. This ensures high cleaning performance, extracting the dirt from the carpet to a depth of half an inch. By immediately reabsorbing the wash water, the drying time is greatly shortened. This method is suitable for intermediate and basic cleaning. Because it does not require cleaning products, it leaves no detergent residue. Vacuum washing has long been in use in Europe, mostly in larger train and bus companies, schools, and historic preservation. The system works on all surfaces which are water resistant (carpet, upholstered furniture, wooden floors, stone, plastics). A great advantage is that this system works without brushes or pads so there is no abrasion on the pile. Household processes Other household carpet-cleaning processes are much older than industry standardization, and have varying degrees of effectiveness as supplements