Soap, consisting of sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.
Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture.
Soaps are useful for cleaning because soap molecules attach readily to both nonpolar molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water.
(fatty end) :CH3-(CH2)n - COONa: (water soluble end) The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification.
The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds. While some people think that this is not really soap-making, the Hand Crafted Soap Makers Guild does recognize this as a legitimate form of soap making or soap crafting. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (glycerin soap), which must be made through the melt and pour process.
Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (superfatting), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, it can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
Reacting fat with potassium hydroxide will produce a soap that is either soft or liquid. Historically, the alkali used was potassium hydroxide made from the deliberate burning of vegetation such as bracken, or from wood ashes.
Soap is derived from either vegetable or animal fats. Sodium tallowate, a common ingredient in many soaps, is derived from rendered beef fat. Soap can also be made of vegetable oils, such as palm oil, and the product is typically softer. If soap is made from pure olive oil it may be called Castile soap or Marseille soap. Castile is also sometimes applied to soaps with a mix of oils, but a high percentage of olive oil.
An array of oils and butters are used in the process such as olive, coconut, palm, cocoa butter, hemp oil and shea butter to provide different qualities. For example, olive oil provides mildness in soap; coconut oil provides lots of lather; while coconut and palm oils provide hardness. Sometimes castor oil can also be used as an ebullient. Most common, though, is a combination of coconut, palm, and olive oils.
Cold-process soapmaking takes place at a temperature sufficiently above room temperature to ensure the liquification of the fat being used, and requires that the lye and fat be kept warm after mixing to ensure that the soap is completely saponified.
Unlike cold-processed soap, hot-processed soap can be used right away because lye and fat saponify more quickly at the higher temperatures used in hot-process soapmaking.
Hot-process was used when the purity of lye was unreliable, and can use natural lye solutions such as potash. The main benefit of hot processing is that the exact concentration of the lye solution does not need to be known to perform the process with adequate success.
Cold-process requires exact measurement of lye to fat using saponification charts to ensure that the finished product is mild and skin-friendly. Saponification charts can also be used in hot-process soapmaking, but are not as necessary as in cold-process.Hot process In the hot-process method, lye and fat are boiled together at 80–100 °C until saponification occurs, which the soapmaker can determine by taste (the bright, distinctive taste of lye disappears once all the lye is saponified) or by eye (the experienced eye can tell when gel stage and full saponification have occurred).
After saponification has occurred, the soap is sometimes precipitated from the solution by adding salt, and the excess liquid drained off.
The hot, soft soap is then spooned into a mold.Cold process A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart, which is then used to calculate the appropriate amount of lye. Excess unreacted lye in the soap will result in a very high pH and can burn or irritate skin. Not enough lye, and the soap is greasy. Most soap makers formulate their recipes with a 4-10% discount of lye so that all of the lye is reacted and that excess fat is left for skin conditioning benefits.
The lye is dissolved in water. Then oils are heated, or melted if they are solid at room temperature. Once both substances have cooled to approximately 100-110°F (37-43°C), and are no more than 10°F (~5.5°C) apart, they may be combined. This lye-fat mixture is stirred until "trace" (modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how your additives will affect trace, they may be added at light trace, medium trace or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding.
The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 18 to 48 hours. Milk soaps are the exception. They do not require insulation. Insulation may cause the milk to burn. During this time, it is normal for the soap to go through a "gel phase" where the opaque soap will turn somewhat transparent for several hours before turning opaque again. The soap will continue to give off heat for many hours after trace.
After the insulation period the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap since saponification is complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2-6 weeks (depending on initial water content) before use. If using caustic soda it is recommended that the soap is left to cure for at least 4 weeks.
Most of the water is then removed from the soap. This was traditionally done on a chill roll which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.
The dry soap (approximately 6-12% moisture) is then compacted into small pellets. These pellets are now ready for soap finishing, the process of converting raw soap pellets into a salable product, usually bars.
Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.
Sand or pumice may be added to produce a scouring soap. This process is most common in creating soaps used for human hygiene. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called exfoliation. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and poor size distribution of pumice.
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient Babylon. A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC.
The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.
A story encountered in some places claims that soap takes its name from a supposed "Mount Sapo" where ancient Romans sacrificed animals. Rain would send a mix of animal tallow and wood ash down the mountain and into the clay soil on the banks of the Tiber. Eventually, women noticed that it was easier to clean clothes with this "soap". The location of Mount Sapo is unknown, as is the source of the "ancient Roman legend" to which this tale is typically credited. In fact, the Latin word sapo simply means "soap"; it was borrowed from a Celtic or Germanic language, and is cognate with Latin sebum, "tallow", which appears in Pliny the Elder's account. Roman animal sacrifices usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.
In semi-modern times soap was made by mixing animal fats with lye. Because of the caustic lye, this was a dangerous procedure (perhaps more dangerous than any present-day home activities) which could result in serious chemical burns or even blindness. Before commercially-produced lye (sodium hydroxide) was commonplace, potash, potassium hydroxide, was produced at home from the ashes of a hardwood fire.
In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. Manufactured bar soaps first became available in the late nineteenth century, and advertising campaigns in Europe and the United States helped to increase popular awareness of the relationship between cleanliness and health.
Rarely, conditions allow for corpses to naturally turn in to a soap-like substance, such as the Soap Lady on exhibit in the Mutter Museum.