So Why Does Shea go Grainy in Botanical Body Care Products?
Understanding Melting Points and Fatty Acids
While each plant-based butter is given a general melting point (e.g. Shea butter has a melting point of 89 to 100°F), the melting point can be a poor descriptor because butters are made up of fatty acids each with differing melting points. For instance, when melting Shea butter the linolenic, arachidic and linoleic acids melt very quickly (they are actually responsible for the slightly ‘moist’ quality of the butter), then the oleic acid, then lauric, then palmitic and finally stearic acid. You can imagine if they melt at different rates they will also solidify at different rates as the butter is cooled.
When a butter, such as shea or mango, is heated the fatty acids separate from one another. Then if you cool the butter slowly, these fractions stay separate causing shea butter to go grainy. Other reasons your shea butter may go grainy include: “the way you’re storing it, the way your supplier is storing it, and possible melting and cooling while shipping from the supplier or from the manufacturer to the supplier.” (Barclay, 2011)
Lets review fatty acids:
Fats and oils consists of up to 95% fatty acids. Fatty acids are hydrocarbons and consist of the elements carbon (C), hydrogen (H) and oxygen (O) arranged as a carbon chain skeleton with a carboxyl group (-COOH) at one end.
There are three types of fatty acids:
Saturated fatty acids (SFAs) contain the maximum possible number of hydrogen atoms attached to every carbon atom and is therefore said to be ‘saturated’ with hydrogen atoms. Saturated fatty acid oils are solid at room temperature. Examples of oils rich in saturated fatty acids include: shea, cocoa and mango all have a high content of saturated fatty acids. Saturated fatty acids have high melting points. Butters are solid because they contain more saturated fats then vegetable oils.
The unsaturated fatty acids have lower melting points than the saturated fatty acids.
Monounsaturated fatty acids (MUFAs) are fatty acids that are missing one pair of hydrogen atoms in the middle of the molecule. MUFAs have only one double bond. One of the most common monounsaturated fatty acids is oleic acid. If you think about oils rich in oleic acid they tend to be fluid unless you put them in the fridge or worse, freezer, at which point they will solidify. Oleic acid rich vegetable oils are also more stable against heat.
Polyunsaturated fatty acids (PUFAs) are fatty acids with two or more carbon double bonds. Examples of polyunsaturated fatty acids include alpha-linolenic acid and linoleic acid. These two fatty acids are considered to be Essential fatty acids (EFAs) as the body does not manufacture them rather they must be taken in the form of food or applied to the skin. Polyunsaturated fatty acids are very unstable and can easily oxidize if exposed to oxygen and light. The presence of tocopherols in oils rich in PUFAs may contribute to their lipid stability. PUFAs include Omega 3 and 6 fatty acids.
Complete Chart of Fatty Acids, Melting Points and Butter %
Avoiding exotic butter formulation pitfalls
Formulating with exotic butters September 2008 – James J. Ramirez, Larry S. Moroni – BioChemica International, USA **To access this article you will need to create a free account on the personal care magazine site. It can be found here: http://www.personalcaremagazine.com/story/3556/formulating-with-exotic-butters
“Cooling rates are important when formulating with exotic butters. This is because a butter’s texture and consistency is directly related to its crystalline structure, all of which are directly affected by its initial cooling rate. As discussed earlier, butters are a mixture of solid (saturated) fatty acids and liquid (often unsaturated) fatty acids. It is this “marriage” between liquid and solid components that is disrupted during the heating and cooling process” (Ramirez and Moroni, 2008). As with an emulsion, particle size (or in the case of butters, crystal size) will have a lot to do with how the butter feels.
If you take a hard, smooth butter and subject it to various temperatures of heat and then various rates of cooling you will have multiple physical expressions of that butter that may range from soft and slightly grainy to a feeling of a semi-solid with grit-like particles being held in it. This is because the solid components of a butter form a crystal matrix that can be visualized as a web of interlocking strands. The smaller and tighter this matrix is, the harder and smoother the butter will be. A smooth butter has been subjected to cooling rates that are optimal for a homogenous mixture of solid and liquid fractions.
Crystallization problems occur when the cooling rate allows for a very gradual reconstitution of this crystal matrix. The interlocking solid strands of the butter that would normally be locking in the liquid fractions within its matrix or web start bonding together in clumps. The result is a butter that has disproportionate levels of solid with solid, and liquid with liquid. This is the cause of problems like leaching and graininess that can be found in butters from time to time.
For Butters and Balms: If a butter’s natural physical properties are desired in an anhydrous formula, then rapid cooling prior to filling, or freezing after hot pouring is recommended. This is specifically for products containing more then 50% shea or similar butters.
For Whipped Butters: The best way to whip a butter that has been melted is to place the melted mixture into the freezer for about 10-20 minutes until the mixture has almost solidified. Then, using a hand held mixer or kitchen aid, whip the ‘solid’ mixture for about 15-25 minutes. The longer you whisk the fluffier the whipped butter will be.
For Body Butters: This takes some degree of experimenting however I have found that typically once all ingredients have been melted down, you can then pour the mixture into jars, close up jars and place in refrigerator for up to 12-24 hours.
Use a Double Boiler: One lesson we have learned over the years is that it does matter what you heat your butters in. We highly recommend a double boiler versus placing a pyrex cup in a pan with water as the double boiler is able to gently heat the shea, mango or cocoa butter (*very important not to over heat cocoa butter!).
Either way, best to use a proper double boiler, even if you simply place a pot on top of another pot to keep the ingredients off of direct heat. The double boiler along with rapid cooling of your butters, should prevent graininess from occurring, unless of course, other factors have come into play as mentioned above (e.g. storage of butter, melting and cooling during transport, etc.).
Interested in learning more?