The greasy basics

Every wonder why some oils are thick, thin, buttery soft or hard as a rock? Want to know the science to why some oils/butters have a long shelf-life? Do you fancy chemistry? Particularly Organic chemistry? You are in the right place. I am going to pretty much explain this as easily as possible. If you want to formulate and not care about the nitty gritty, tune into future posts that are not so scientifically oriented. We will add an oil, butter and/or wax every three to four days, so check us out.

Triglycerides have a glycerol back bone and three fatty acid chains.  Saturated fatty acid chains have no double bonds, a fatty acid chain with double bonds are called unsaturated, chains with a single double bond are called monounsaturated, and a chain with greater than one double bond is called polyunsaturated, are you still with me? The image above is unlikely but a perfect example of a triglyceride, a triglyceride usually does not have three identical chains.

Those chains with a single bond (saturated) are least likely to oxidize because those bonds are harder to break. Expect saturated fats to be able to hang around longer before they become rancid. Fatty acids with double bonds are not very stable and go rancid more quickly, especially those with polyunsaturated chains. Utilizing lipid numbers, you can tell how many bonds there are in a fatty acid. Ex. C18 (stearic acid), C18:1 (oleic acid), C18:2 (linoleic acid) and/or C18:3 (alpha-linolenic acid). These are lipid numbers. The letter C is the carbon atom, the number after the letter C represents the number of carbon atoms within the fatty acid and the final number after the colon is how many double bonds within the fatty acid chain.

HYDROGENATION

So fatty acid chains with double bonds can be broken and tend to react with oxygen causing oxidation. Some manufacturers hydrogenate oils by breaking the double bond and placing hydrogen into those open sections. They basically have created a saturated chain. I haven't seen much research on hydrogenated oils in skin care, but have heard a lot about why we shouldn't eat hydrogenated oils. The plus side to hydrogenated oils is that they are now going to have a longer shelf-life and becoming rancid early has been decreased, plus they look more like a butter.

So why are some oils solid and some liquid? It is all in the shape of the fatty acids. Saturated fats pack in nicely together because they form a straight line. So they tend to be more solid. When the fatty acid has a double bond, it forms a bit of a kink, and in some cases, a bend. Those double bonds can't play close together and oils with these bonds tend to be more liquid at room temperature. See pic below.

DOUBLE BOND TERMINOLOGY

So, have you been seeing Cis- or trans- ? This terminology is seen when describing the double bond on a fatty acid. Cis- is when the hydrogen atoms at the double bond occur on the same side of the bond. These chains have a bend at the double bond. These also tend to be more liquid and have a shorter shelf-life.

Trans- has the hydrogen atoms on opposite sides of where the double bond occurs. These chains tend to be straighter. The lay nicely together and make a thicker product that has a longer shelf-life.  Trans- in a sense, behave more like they are saturated fatty acids.

Partial hydrogenation basically turns a "cis-" bond into a "trans" bond using a chemical process. Trans- fats are rarely a natural occurance.



As a home crafter, if you know the properties of oils and butters you plan on using in formulating recipes, you can figure out if the final product will have a short or long shelf-life. No double bonds makes a butter (long shelf-life), many double bonds and light oil (shorter shelf-life), few double bonds makes a heavy oil (longer shelf-life than lighter oils).

Look for my next blog,  I will discuss the fatty acids commonly utilized in the soap-making process.

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