Updated: Jul 24, 2019
Modern day soap making is so exciting because there is SO much information and many ingredient options available. You can truly make a one-of-a-kind soap. There are millions of different combinations of oils, butters, additives, liquids and other ingredients. There are quite a few recipes available right now that are highlighting one ingredient in particular: apple cider vinegar (or just plain vinegar).
The claims about using apple cider vinegar are vast and there are blogs and YouTube videos that proclaim that vinegar in soap making helps create the biggest and most abundant lather, turns a regular soap recipe into a shampoo soap, chelates minerals from hard water, reduces oxidation and dreaded orange spots, is the difference between a conditioning bar and a drying bar, and so much more. From these claims, it sounds like vinegar truly is an "all-powerful" ingredient, but does it live up to the hype? Let’s take a look at this ingredient and see how it reacts in your soap recipe. Does vinegar actually have the all of these claimed benefits? Is it the blessing people talk about or can these claims be busted?
Everyone who reads this article has probably had some sort of interaction with vinegar, whether it was for cleaning purposes, the flavor of your favorite salt and vinegar chips, or perhaps you used in your grade school volcano science project. For soap makers, having a solution of vinegar prepared and ready during soap making is essential because it can be used to clean up any lye spills and should be part of your lye safety arsenal.
But what exactly is vinegar? Vinegar is actually a very simple solution that consists of water and 5% acetic acid. Apple cider vinegar or ACV is a subtype of vinegar that is created from the production of alcohol from apples. Both classic white vinegar and apple cider vinegar are acetic acid solutions.
When an acid is combined with a base, a salt is formed. Soap itself is a salt and is created by the combination of fatty acids and sodium/potassium hydroxide. When acetic acid combines with our basic lye solution, the salt sodium acetate is formed. Although many people believe that sodium acetate is a chelator, or a chemical that has the composition capable of binding to and trapping minerals rendering them unable to bind with other chemicals, sodium acetate does not have the chemical composition or structure to be considered a chelator. It does not have the chemical composition that is capable of "trapping" minerals like other chelators, such as EDTA or sodium gluconate. Without the ability to prevent metals and other contaminants like calcium and magnesium from binding to the soap molecules, sodium acetate does not have the ability to chelate in the samr manner.
Many people also claim that sodium acetate can reduce the risk of oxidation and prevent DOS, but unfortunately, without a chelating or antioxidative composition, it is not capable of effectively reducing DOS like many people claim. There have been multiple tests done by prominent soap researchers, including tests that we have done, that have shown that sodium acetate is not an effective chemical for reducing rancidity and did not prevent the oxidation and formation of DOS in the final test results.
If you are adding vinegar to your soap for its chelating and/or antioxidant effects, consider another additive that has tested and research-backed results, including EDTA, ROE, sodium citrate, sodium gluconate, and BHT. EDTA (Sodium Ethylenediammine Tetraacetate) and sodium gluconate have been shown to be efficient as both a chelator and in the prevention of catalytic oxidation. Rosemary Oleoresin Extract (ROE) is a natural chemical compound found in rosemary that is an effective antioxidant. Sodium citrate is the sodium salt created by combining sodium hydroxide with citric acid. Sodium citrate is another option for chelating and possibly prevention of DOS. Citric acid can be purchased in powdered form or found naturally in citrus juices. The combination of Butylated Hydroxytoluene (BHT) and sodium citrate has been studied in multiple tests and found to be very effective at preventing rancidity and oxidation.
Another common claim that many soap makers have been making is that by adding vinegar to soap, you can use a low superfat and still create an intensely conditioning bar. In fact, this is recommended by several of the most popular shampoo bar soap makers who believe that shampoo bars should contain no more than 1% SF and should be made with 100% vinegar in the lye solution.
What happens when we use vinegar in the lye solution? If we combined vinegar (which is a solution of acetic acid and water) with sodium hydroxide to create a lye solution, a portion of the lye solution would be "consumed" and turned into sodium acetate. Remember, when we add an acid to a base, it creates a salt. Acetic acid (acid) and sodium hydroxide (base) create the salt sodium acetate. Because a portion of the lye is used to create sodium acetate, there is less lye in the solution to break the triglyceride bonds and saponify the recipe's oils. Using vinegar creates a lye discount, or more commonly called, a superfat. This is the opposite of using a low superfat.
Adding vinegar to your recipe and using it for the lye will increase the recipe’s superfat by approximately 6.6% because of the total amount of lye needed to break down acetic acid. Many recipes state that shampoo bars require a very low superfat, yet they should be made with an acidic vinegar lye solution. If the recommended SF is 3%, using a vinegar lye solution will result in a 9.6% SF, which is not a low superfat. This is actually a pretty significant increase and can affect the soap's qualities, increase the softness of the bar, and it significantly increases the risk of rancidity and oxidation, including dreaded orange spots. When people claim that adding vinegar to soap lowers the pH, it only does so because it slightly increases the superfat.
But what if we add the vinegar after the cook in a hot process soap, won't it lower the pH then? Adding vinegar after the cook will precipitate and free some of the fatty acids, and will lower the total pH of soap solution through a process called acidifcation (not the actual soap and it is important to note that this will be a very insignificant amount). Free fatty acids increase the risk of oxidation, and so does the increase of water in the soap bar through a process called hydrolytic oxidation (remember vinegar is 95% water). It should also be noted that the process of acidification naturally occurs over time due to the acidic carbon dioxide present in the air. This process doesn't require the addition of more chemicals or liquids. Acidification by carbon dioxide won't have an impact and lengthen your soap's curing time and it won't increase the possibility of warping due to the increased water content.
What if you are dead set on using vinegar in your recipe? If you must use vinegar in your recipe and still follow the other suggestions set forth in some of these popular recipes, like using a low superfat, you can neutralize the solution before hand with sodium bicarbonate (baking soda), use a 0%SF with the understanding that vinegar will add approximately 6.6% SF, or you can calculate and add additional lye. Each gram of vinegar consumes 0.033 grams of sodium hydroxide. For every gram of vinegar you use in your lye solution, an additional 0.033 grams of NaOH should be added to prevent additional SF and accommodate for the sodium acetate.
There are many different claims and people absolutely rave about some of the more popular ACV recipes, but to me, the ingredient doesn’t live up to its reputation, especially when there are other more documented and viable options for these reported benefits. For me, vinegar is a bust. Luckily, as soap makers, we have the freedom to formulate our recipes however we choose, so long as they are informed and made with intention.
Do you use vinegar or ACV in your recipes? Share more below!
Looking for added bubbles and lather stability in your soap, be sure to check out our What The Suds: Cetyl Alcohol Experiment. Are you a beginner or new to fatty acids? Check this article out to learn about the importance of fatty acids in soap making!