From the shelled seeds of the Ricinus communis L. (castor beans), which have an oil content of 40-50%, castor oil can be obtained using a mechanical, cold-press process. The resulting oil must subsequently undergo a refining process, however, to prevent the toxic ricin from ending up in the oil. Although the quality of the cold-pressed castor oil is better, it is also possible to use a hot-press method for the shelled castor beans, which advantageously increases the degree of extraction. For this, the beans are heated prior to being pressed and then fed into a screw press, resulting in crude oil and castor press cake. The press cake nevertheless still contains around 10% oil, so that an additional extraction using hexane, heptane or a mixture of the two can be used to obtain a larger amount of oil. After the solvent is removed from the extraction residue, only around 1% of the oil remains in the castor meal. The oil obtained through both of the production methods then undergoes a refining process consisting of degumming, de-acidification, and then a steam treatment of the oil. The toxic ricin thereby remains not in the oil, but in the press cake, thus making the oil suitable for therapeutic purposes. If the leftover proteins are to be removed from the oil, then a process known as degumming ensues, which involves adding 3-5% water, heating it to 70-80°C, and then removing the water using a centrifuge. Free fatty acids can also be eliminated with the aid of an alkaline solution. Here, however, the castor oil tends to emulsify, and therefore needs to be watched. Futhermore, the oil can be clarified and decolorized by heating the oil to around 80°C and adding small amounts of surface-active clay minerals; to darken the oil, however, tiny amounts of activated carbon can be added. Finally, by heating the oil in thin films in a vacuum (thin-film evaporator) for a short time to 230°C, the volatile compounds and odorants can be largely removed. In contrast to many other press cakes which arise during the oil production of seeds and kernels from various plants, untreated castor press cakes – despite their high protein content – cannot be used in animal feed production. For this they must first undergo a process to remove all the toxic substances (particularly ricin and ricinine) and allergens contained in the press cakes. Untreated press cakes from the pressing and extraction meal from the extraction are normally further processed into nitrogen fertilizer (castor meal).
Characteristics and shelf life
Castor oil is clear, being nearly colorless to yellow tinged, and forms a flammable and viscous liquid.The faint yet characteristic scent of this oil is reminiscent of damp paper, smelling slightly herbaceous and woody. Although it is nearly tasteless, it nevertheless features a characteristic, somewhat unpleasant taste. The solidification range of this oil is between -13 to -20°C; the melting point, approx. -5°C; and the flash point, around 229°C. Furthermore, it is ranked among the most highly dense oils and, since it breaks down around 250°C, it is not distillable. Further characteristics of castor oil are that it belongs to the group of non-drying oils, since it indeed becomes thicker when exposed to air yet does not harden in thin layers; and, due to its high percentage of hydroxy fatty acids, it possesses a high polarity. This makes it highly soluble in ethanol, yet difficult to mix with aliphatic hydrocarbons and lipo-insoluble. Castor oil contains around 80-85% triglycerides of the unsaturated ricinoleic acid (also called ricinolein). It additionally contains other glycerides of various C18 fatty acids and several volatile compounds (acetic acid, heptanol, octane, hexanol, styrene, alpha-pinene, propenoic acid butyl ester, etc.). The fatty acid composition of the oil is divided as follows: 77-83% ricinoleic acid, 3-5% linoleic acid, 4-9% oleic acid, 1-2% palmitic acid and 1-3% stearic acid. Tiny amounts of vaccenic acid, apha-linoleic acid, arachidic acid, and eicosenoic acid can also be found in the oil. What is more, castor oil features a free fatty acid content of 0.75-3.0%, a water content of 0.25-0.5%, and .01-0.2% leftover impurities.
Castor oil normally has a shelf life of 6-8 months.
Pharmaceutical and medical use
The books Öle – natürlich kaltgepresst (oils – naturally cold-pressed) by Marcus Hartmann and Lexikon der pflanzlichen Fette und Öle (lexicon of plant fats and oils) indicate that (refined) castor oil has a wide variety of uses in the realm of pharmacy and medicine. Thus, on the one hand it can serve as an effective laxative in the case of constipation, and to accelerate the emptying of the bowls; on the other hand, due to its comparatively high polarity, it can serve as a good solvent for many medicinal products. Furthermore, castor oil, being highly viscous and a poor breeding ground for microorganisms, makes a good additive in eye drops. This oil is also often used for injection purposes, in order to administer lipophilic medicinal products that cannot be taken orally. In particular, sexual hormones with depot effect are applied in the form of oily solutions (vials and intramuscular application). Finally, castor oil is also used topically. It possesses the beneficial characteristic of being able to penetrate well into the intercellular space of the cornea. Topical application of this oil helps treat scales, scar formation, age spots, and hemorrhoids. In the area of dermatology, it can be used as an emollient. Another beneficial characteristic of this oil is that it forms a mechanical protection against water and harmful hydrophilic substances; under this protective barrier, lesions and fissures can heal more quickly. Castor oil, due to its high solubility in ethanol, is also readily used as a fat addition to Kopfspiritus (an ethanol mixture used to treat hair loss) and other alcohol-based external products. This oil is furthermore sometimes administered in obstetrics as a “labor cocktail” to induce labor. Beyond this, the ricin, which occurs naturally in castor oil, is currently being tested in tumor therapy because of its cytostatic (growth inhibiting) effect on cancer cells.
In folk medicine
In natural medicine, castor oil is used to relieve mastitis, loosen stiff arthritic joints, increase the function of congested lymph glands, and strengthen the immune system. This oil also is also supposed to be able sooth herpes ailments and neutralize spasms and blockages in the abdomen. Furthermore, films of hot castor oil are supposed to have a positive effect on colitis and ulcerations; and stimulate the digestive system.
Castor oil commonly appears in cosmetic products because of its high viscosity and its good solubility in ethanol. It is often found in brilliantines, hair care products and mascaras; and is used with emulsifiers in bath oils to help against dry skin. Additionally, this oil can penetrate intracellular spaces well – those of the cornea, for example – and is therefore readily used in treatments for dandruff, scars, age spots, and hemorrhoids. It can also aid in healing lesions and fissures since it forms a mechanical protective film against water and harmful water soluble substances. Furthermore, castor oil can also serve as the basic material in the production of lipsticks, cosmetics and shampoos, whereby the ricinolein contained in the oil is significant because it helps skin and hair retain their oils and smoothness.
Castor oil has a wide variety of technical uses. It can be used, for example, in the production of soaps, paints, dyes, inks, waxes, polishes, and cold-resistant plastics; as well as nylon, pharmaceutical products, and fragrances. This oil is also important as a lubricant for motors (for example, in jet engines) or as brake fluid, since its viscosity, being largely independent of temperature change, remains virtually constant. In addition, the use of castor oil as natural polyol in polyurethane plastics is of considerable significance. This oil represents the only plant oil (available in large amounts) that naturally possesses the OH-functionality necessary for reacting with di- or polyisocyanurate to make polyurethane polymers. This is then used for PU foam (in cushions, mattresses, and foam insulation), casting resins, and glues. Castor oil also constitutes a good binder for lacquers and paints, varnish, linoleum, and printing ink. In addition, it is deemed to be a good starting material for polyamides and polystyrenes, and it suitable for preparing sebacic acid, which is used in fabric softeners. Castor oil also serves in the production of Turkey red oil, which is readily used as a coloring agent (stain) in the textile industry because of its wetting properties and emulsifiability. It is also found in bath oil products. Furthermore, castor oil, when transestrified first, aids in the production of biodiesel. The oil, by undergoing a pyrolytic decomposition into heptanol and undecenoic acid, also serves in the manufacture of flavoring agents and aromatic substances; as well as in the medical arena, to treat fungal infections and skin parasites. If the undecenoic acid esters are further processed, then an important polyamide arises that serves as a high-performance plastic for fibers and various technical applications in coatings, cables, and automobiles. Finally, polyester can also be obtained from castor oil. To achieve this, the monomers citric acid and ricinoleic acid are left under polycondensation to react with one another, thus forming an ester, whose name polyester is derived from the process. Water is separated off during the ester formation, finally leaving behind a brownish, sticky, water-insoluble resin. The oil cake and the meal that arise as byproducts during the oil pressing are first detoxified through heat inactivation, and then are used in the production of animal feed or organic fertilizer.
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In addition to their own knowledge acquired through press trials, the following sources were used to create the article:
- Öle, natürlich kaltgepresst, Basiswissen & Rezepte, Marcus Hartmann, Hädecke, 2008
- Heilende Öle, Pflanzenöle als Nahrungs- und Heilmittel, Neue Erkenntnisse, Günter Albert Ulmer Verlag Tuningen
- Lexikon der pflanzlichen Fette und Öle, Krist, Buchbauer, Klausberger, SpringerWienNewYork, 2008