Sugar in Soap Making: How it Affects Saponification, Lather, & More- Plus, Why Every Recipe Needs It
Updated: Sep 8, 2019
One of the best parts about making handcrafted soap is the “testing period”. This comes after you have spent countless hours studying and learning how to successfully formulate informed recipes that are created with the perfect blend of fatty acids and your own custom blend of additives, not to mention, you have waited patiently for your soaps to fully harden and cure. Watching that rich, white, full, and bubbly lather form is almost as if they soap is yelling “Yes! You did it! Job well done!”
Ok, so maybe our soaps don’t exactly yell at us, but the performance and soap properties can certainly give us some insight into our recipe formulating strategies and provide us with ample information for future batches. As a handcrafted soap maker and an UG2HP student, you know that the most important aspect of recipe formulating is studying and creating a fatty acid composition that suits your needs and desired soap properties, whatever they may be. These little fatty acids control everything about your soap- how hard or soft it is, how bubbly or creamy it will be, if it will be short-lived or long-lasting, and so much more. (New to soap making? Read more about Fatty Acids for Beginners here)
After reading The Ultimate Guide to Hot Process Soap, you also know that in addition to a fatty acid blend that supports a rich and bubbly lather, there are optional additives that can be included to enhance these super sudsy properties. Some of these suggestions include the addition of a chelator such as citric acid to form sodium citrate or sodium gluconate to help combat hard water, cetyl alcohol or jojoba oil for increased lather stability, a eutectic blend of sodium laurate and sodium oleate, and one of my personal favorites- SUGAR.
So, what exactly is sugar and how does it affect our soap? Sugars are chemicals that consist of carbon (C), oxygen (O), and hydrogen (H) atoms, and can be classified broadly as a carbohydrate. There are three main groups of sugars, classified according to the way the atoms are arranged together in the molecular structure. These include monosaccharides, disaccharides, and polysaccharides (saccharide derived from the Latin term for sugar). Monosaccharides (mono-one) are simple sugars that consist of only one molecule and include glucose, fructose (found in honey and fruits), and galactose (milk sugar). Disaccharides (di-two) are more complex sugars and include sucrose (table sugar), maltose, and lactose (milk). Polysaccharides (poly-multiple) are even more complex and include starches, dextrins and cellulose (plants).
When a soap maker makes the suggestion “add sugar for extra lather,” they are most often referring to the disaccharide sucrose, more commonly known as table sugar. Sucrose is a molecule that is comprised of 12 atoms of carbon, 22 atoms of hydrogen, and 11 atoms of oxygen or C12H22O11, which can also be written as C12H14O3(OH)8. Sucrose is actually a combination of the two monosaccharides fructose and glucose. Another common sugar used in soap making is found in milk (goat milk soap anyone?) and is called lactose. Lactose also has a chemical formula C12H22O11 or C12H14O3(OH)8. Notice something about each of these? Both sucrose (table sugar) and lactose (milk sugar) both have eight OH groups.
What the heck is an OH group and what does it mean for our soap? An OH group, or a hydroxyl group, is comprised of both an oxygen and hydrogen molecule. Sucrose and lactose both have eight of these OH groups (see the image above). These OH groups comprise a large portion of the sugar molecule and are hydrophilic, or water loving (hydro-water and phillic-loving). This is in comparison to the relatively small hydrophobic or water fearing part (hydro-water and phobic-fearing).
What does this mean? This means that sugar molecules have both a hydrophilic (water loving) end and a hydrophobic (water fearing) end, and that they are more hydrophilic (water loving) than hydrophobic (water fearing). Because of this, sugar is very soluble in water. If you added a few spoonfuls of table sugar to a cup of water and stirred the mixture, what would happen? It would rapidly dissolve to a clear solution in a matter of seconds.
What else in our recipe has both a hydrophilic and hydrophobic end? Our soap of course! Soap molecules also have both a hydrophobic fatty acid end and a hydrophilic head. These characteristics allow soap to function as a surfactant because it can bind to dirt and oil molecules at the hydrophobic end and bind to water molecules at the other hydrophilic end. This allows dirty oil molecules to become trapped in little micelles which can then be washed away with water. (We covered this extensively and with fun video tutorials in UG2HP!)
Unlike sugar molecules, the hydrophobic, or water fearing end of a soap molecule is much larger than its hydrophilic, or water loving end. This means that soap is more hydrophobic than it is hydrophilic, which makes it less soluble in water than sugar. Isn’t that bad? Don’t we want soap to be extra water soluble so that it dissolves when we need it?
In bar soap, its more hydrophobic nature is actually a good thing! We don’t want soap to be too hydrophilic; otherwise it wouldn’t last very long. Because soap has larger hydrophobic fatty acid end, it is able to withstand daily use in the shower. If you added a bar soap to a glass of water and stirred, what would happen? The bar of soap would swirl around with your spoon, and only after a very prolonged period of time and lots of agitation would it dissolve. These chemical properties are what allow us to drop a bar of soap in the shower, and still pick it up and be able to use it without it completely dissolving in our hands (like sugar would!)
So now that we know that sugars have a more water loving end than soap molecules, how does this affect our soap? Because of their chemical properties, sugar molecules are able to gather around the hydrophilic end of the soap molecule. This makes soap molecules more attractive to water molecules, which can have some pretty amazing effects on our soap.
During the saponification process, the addition of sugar will accelerate the rate of trace, which is really a visible sign that an emulsification has formed. The accelerated rate of emulsification leads to an accelerated reaction rate, which requires less time for our recipe to saponify and produces an even more exothermic reaction. Sugar also makes soap molecules more attractive to water after production, which increases the rate at which soap is dissolved during use. By increasing the solubility of soap, it decreases the amount of work energy and rubbing necessary to create lather. The OH groups in sugar act in a similar fashion as the OH groups in sodium ricinoleate, the soaps produced from the saponification of castor oil, and we know how awesome castor oil is in our recipes!
Surface Tension and Bubbles
Sugar not only accelerates the rate of emulsification, saponification, and lather formation, but it also affects water tension. Soap molecules affect the surface tension by increasing the distance between water molecules and reducing those molecules' ability to interact with each other. This decreases the attraction the water molecules exert on each other, lowering the surface tension of the solution.
Soap lowers the surface tension of water to about 1/3 of that of pure water and by doing this, it allows the bubbles to last longer. This is why soapy water bubbles are able to last much longer than just the bubbles that are formed from water alone.
A common recipe for children’s play bubbles is comprised of water, dish soap, and glycerin or corn syrup. Both glycerin and corn syrup contain chemical compounds that include sugars and/or sugar alcohols, all of which have OH groups. Although bubbles can be made from just dish soap and water, by adding an ingredient like glycerin or corn syrup, the bubbles produced are able to last much longer. Bubbles that are formed burst when the layer of water molecules between the soap molecules evaporate, but when compounds like glycerin or corn syrup are added in conjunction with the soap, it forms weak bonds with the water molecules and slows down the evaporation process. Because the evaporation process is slower, it significantly improves the lifespan and the durability of the bubbles. Glycerin and sugar make stronger, longer-lasting bubbles. Glycerin is naturally produced by saponification and with added sugar, we get the best of both worlds.
Feel like your brain is going to explode from all this sugar science?
Let’s simplify and review- sugar is an amazing additive in soap making. It is such an awesome additive that chemists and cosmetic chemists are learning how to use sugar to help create new and exciting surfactants and detergents that create larger, bigger and fuller bubbles, that form at a faster rate. Sugar has the power to accelerate trace, accelerate the overall reaction rate, accelerate the transition to gel phase, increase the rate of lather formation, positively change the lather texture, increase the lifespan of bubbles, and increase the durability of bubbles. I would say that sugar is well worth its reputation and now you know why.
How to Use Sugar in Soap
So now that we know what sugar does and how it does it, how can we include it in our recipe formulations to take advantage of the benefits it has to offer? Sugar can be added at different times during the process of soap making. You can add it to the lye solution, to the oils, or at trace to help accelerate the reaction rate and to help with the lather. In hot process soap making, you can also add it at gel, after the cook, or even sneak it in with your colorants. We all know that I love to add sugar to both my lye solution for its emulsion and saponification accelerating benefits and also to my colorants for an increase in the lathering and bubble stability benefits (not to mention that it makes mixing colorants in hot process a smooth and seamless process, with bolder brighter colors).
How much sugar can we add? Sugar is commonly added at anywhere from 0.5-5% of the total oil weight. I most commonly use 4% of the total oil weight pre-cook and 1% of the total oil weight in my colorants. Sources of sugars can include table sugar, goat milk, cow milk, coconut milk, honey, molasses, fruit juices, and more.
Sorbitol in Soap Making for Extreme Lather and Softening
I have personally switched from sucrose (table sugar) to sorbitol, a sugar alcohol that is commonly used in cosmetics and baking. It can be purchased from cosmetic suppliers, baking stores, and online retailers like Amazon, and it is available in a white powdered form or a liquid sorbitol solution. I purchase mine in powdered form and create my own solutions because it is much more economical. Sorbitol not only provides all of the same benefits of sugar, but it significantly increases the rate of lather formation, holds the bubbles better, is a humectant and it has skin-conditioning benefits. Sorbitol can also be used in other cosmetics and is a primary solvent in transparent soap making, so it serves multiple purposes in my cosmetic arsenal.
Out of all of the sugar sources that I have used, sorbitol is by far my absolute favorite sugar-like additive and it goes into every recipe that I make. I combine all of the tools and resources from The Ultimate Guide to Hot Process Soap to create The Ultimate Lather and everyone who receives my soaps absolutely adores them.
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Do you use sugars in your soap recipes? Feel free to share your favorite experiences or questions below!