The shea tree, lat. Vitellaria paradoxa, belongs to the Sapotaceae family and can be found in the regions of the Sahel and the Guinea zone. It reaches a height of about 5-12 meters with large leaves that grow in clusters at the end of the branches. If the tree blooms in spring, up to 100 cream-white flowers can be found, which are also arranged in clusters on the branches. Only after 10-20 years the tree grows fruits and after 40-50 years it reaches its maximum yield. The ripe fruit has a size of about 4x6 cm. It consists of a thick edible skin and a chestnut-like seed.
Today's main producers are almost all located in Africa: Mali, Ivory Coast, Burkino Faso, Senegal, Ghana and Nigeria. The world's largest producer is Nigeria, which covers almost two thirds of the world's demand (approx. 600,000 t).
Depending on the region, the fruits get picked between May and August almost exclusively from wild trees. Since the tree bears its first fruits only after 10-20 years, plantation cultivation does not seem to be reasonable or financially attractive so far.
After the harvest, the green outer skin (epi- and mesocarp) is removed to prevent microbial decay. Removal can be done manually or by fermentation. If the fruits are stored too long (>3 days) before removing the outer skin, microbial decay of the fruits may occur. This happens as the outer skin contains sugar, which promotes fungal or bacterial attack. If the fruit is stored incorrectly or for too long, this leads to a reduction in the quality and quantity of the obtained oil. The remaining nut or seed with the contained fat has a brown or dark yellow color.
To prevent further enzymatic decay in the nut, it is treated with heat. During this process the nuts are boiled for 15-45 minutes, roasted in a drum or dried over an open fire (with smoke). The heat energy applied not only kills harmful enzymes, but also destroys the oil cell structure in the seeds. Thus the oil yield can be further increased. Another effect is "cleaning" the outer skin from remaining fruit flesh.
After cooking, the nuts get dried even further to remove all of the contained water. This is usually done in the sun for 5-10 days, or with the help of an oven for 2-3 days. During the drying process, the seeds slowly detach from the shell and can be removed more easily in the following step. The outer shell of the nut is now opened mechanically or by hand and the oily seed is revealed. The broken shells are removed and usually processed into fuel.
The shea butter is contained within the seed to about 60% and can be extracted by three common methods: the traditional, mechanical and chemical method.
For the Black Shea Butter, the seeds are roasted again before being crushed. This additional process gives the obtained butter a black color. The product obtained is usually only used for culinary purposes.
In order to save time and money, mechanical methods have been increasingly developed. These are based on the classic methods of cold pressing or centrifugation. Both methods work according to the same principle: by means of shear forces the cells are broken up and release the oil (centrifuges have to supply additional thermal energy and water). The oil obtained is filtered again and then cooled. Once this step is completed, the shea butter is obtained.
In the chemical method, a paste is also produced first, which is then placed in a Soxhlet apparatus. The oil is then extracted from the paste using organic solvents. Finally, the solvent is removed from the mixture using vacuum and heat, leaving the shea butter as a residue.
In order to market a consistent product, the shea butter is often refined. The product is thus precisely adjusted to physical and chemical parameters, whereby a loss of some natural substances is accepted.
In the food industry, shea butter can sometimes be used as a substitute for cocoa butter or frying fats.
Shea butter has a very different composition due to its different locations and processing methods. Exceptional, compared to other oils such as avocado oil, is the high content of unsaponifiable substances with up to 11%. Shea butter has a very high proportion of stearic, oleic and linoleic acid as well as vitamin E and beta-carotene.
The cosmetics industry is increasingly using shea butter in ointments, creams and lotions because it is easy to apply to the skin and leaves a greasy film (the melting point varies from 32-45 degrees Celsius). The skin becomes smoother and does not dry out as quickly. The good tolerance also makes the shea butter appear as an additive in lip balms or in anti-pregnancy strips. Shea butter itself has a sun protection factor of three.
A medical study indicates a positive effect in lowering LDL cholesterol. In this study, several volunteers were given shea butter as a substitute for sunflower oil. It showed a decrease in total cholesterol, with only LDL cholesterol being reduced. A positive HDL/LDL ratio could thus serve to prevent coronary artery disease or similar diseases.
Another positive effect seems to be seen in the treatment of skin diseases: The triterpene alcohols amyrin, lupeol and butyrol spermol could stop inflammatory processes. These substances inhibit collagen- and elastin-degrading enzymes in the skin. The result is a stronger and more resilient skin. Particularly in the case of scaly dermatitis and dry skin in old age, results could be achieved with products containing cortisone.
Incorrect storage after harvesting or during the drying process of the nuts (especially drying in the sun) can lead to fungal or microbial infestation. This has a negative effect on the quality and quantity of the oil. If an untreated oil is required, it is recommended to carry out a test from microorganisms. A possible indicator can also be a low value of phenols or some fatty acids (linoleic acid, etc.), since enzymes from microorganisms lead to a faster degradation of these.
One of the most important steps is the roasting process: haptics and sensory properties were especially influenced by the heat input and duration of this process.
New methods try to increase the yield mainly by using enzymes. Lipases, amylases, cellulases and other enzymes are used to improve the structure of the seeds. The subsequent extraction can thus lead to an even higher yield.