A common process of hot water extraction  begins with preconditioning. Alkaline agents such as ammonia solution for synthetic carpets, or acidic solution (such as vinegar solution) for woolen carpets, are sprayed into the carpet, then agitated with a grooming brush or an automatic scrubbing machine. Next, a pressurized manual or automatic cleaning tool (such as a wand) passes over the surface to rinse out all pre-conditioner, residue, and particulates. If an alkaline detergent is used on a woolen fibre, use of an acetic acid solution will restore neutral fiber pH. The acid rinse thus neutralizes the alkaline residues, and can contribute to softening cleaned fabrics. The hot water extraction method is the preferred method of many carpet manufacturers. Extraction is, by far, the most important step in the hot water extraction process. Since the hot-water extraction method uses much more water than other methods like bonnet or shampoo cleaning, proper extraction and air flow are critical to avoid drying issues. Drying time may also be decreased by extra use of fans, air conditioning, and/or outdoor ventilation. Older surfaces, such as double jute-backed carpets and loose rugs with natural foundation yarns, could shrink after a wet treatment, leading to suppositions that wet-cleaning could also remove wrinkles. However, this notion is antiquated and this method could also occasionally tear seams or uproot strips. Newer carpets, such as with synthetic backing and foundation yarns, do not shrink, and they smooth easily; in such carpets, wrinkles indicate an underlying problem, such as adhesive, that may need a certified carpet inspector to determine. Wet-cleaning systems naturally require drying time, which may lead to concerns about very slow drying, the risk of discoloration returning during drying, and odors, bacteria, fungi, molds, and mildews. Carpet cleaning specialists try to find a balance between rapid drying (attributable to lower flow rate through the cleaning jets of a spray system) and the need to remove the most soil (attributable to higher flow rate).
Unsourced material may be challenged and removed. (March 2015) (Learn how and when to remove this template message) A 98% biodegradable or others, slightly moist absorbent cleaning compound may be spread evenly over carpet and brushed or scrubbed in. For small areas, a household hand brush can work such a compound into carpet pile; working like "tiny sponges", the attracted cleaning solution dissolve dirt, dirt and grime is attracted/absorbed to the compound, after a short drying time (the cleaning solution which is attracted to the compound must evaporate), it will be removed with a vacuum cleaner, the drier the better, leaving carpet immediately clean and dry. But it's very difficult to remove all residues, the residues can cause allergies and biological compounds may cause discolourations on carpets. For commercial applications, a specially designed cylindrical counter-rotating brushing system is used, without a vacuum cleaner. Machine scrubbing is more typical, in that hand scrubbing generally cleans only the top third of carpet. Encapsulation In the 1990s, new polymers began literally encapsulating (crystallizing) soil particles into dry residues on contact. In the conventional cleaning process surfactant molecules attach themselves to oily soil particles, suspending them (emulsification) so that they can be easily rinsed away. Surfactant (detergent) molecules and emulsified soils which escape being rinsed away, remain in the fibre and continue to attract soiling, causing the condition of the carpet to degenerate; often re-soiling faster than before it was subjected to the cleaning process. Encapsulators are speciality detergent polymers which become part of the detergent system. As drying occurs (20-30 min. drytime), after cleaning, these encapsulators bind the detergent molecules and residual soils in a brittle, crystalline structure. Detergent and soil particles can no longer attract other soils and are easily removed by dry vacuuming. In addition to binding the detergent and soil residues the encapsulation chemistry coats the clean fibre with the same brittle film. This reduces the fibre’s affinity for oily and particulate soils. As this brittle film"breaks away" and more soil is removed, the appearance of the fibre improves as opposed to soiling more rapidly. Products which also employ fluorochemical technology, display dramatically extended anti re-soiling time periods. Cleaning solution is applied by rotary machine, brush applicator, or compression sprayer. Dry residue is vacuumable immediately (20-30 min. drytime), either separately or from a built-in unit of the cleaning-system machine. According to ICS Cleaning Specialist, evidence suggests encapsulation improves carpet appearance, compared to other systems; and it is favorable in terms of high-traffic needs, operator training, equipment expense, and lack of wet residue. Encapsulation carpet cleaning also keeps carpets cleaner for longer periods of time compared to other methods.