If you don’t know what I’m referring to about soap sweating, then consider yourself a lucky soapmaker so far! The rest of you know what I’m talking about! You’ve just made some lovely melt and pour soap. After it’s hardened, you pop your beautiful soap bars out of their molds and then the next day you see it. It looks like frost or fuzz at first, upon closer inspection you see hundreds of tiny little water droplets covering the surface of your soap. There’s another name for this phenomenon, it’s also called glycerin dew (that sounds nicer, hmm?)
What causes soap to sweat?
Melt and Pour soap base contains glycerin, an organic compound also known as glycerol. It’s a clear, odorless liquid at room temperature and is derived from animal fat and vegetable oil. It’s also a natural byproduct of the saponification process. Glycerin is a humectant / hygroscopic. That means it absorbs and attracts ambient water. If you left a cup of glycerin out in a humid room, it would actually absorb water from the air until it was about 20% water. In soap, glycerin helps moisturize your skin and seal in moisture. Glycerin is a key ingredient for making clear soaps. Okay so what is the point here?
The glycerin content in your soap actually causes your soap to become hygroscopic and so if your soap has a high level of glycerin in it and you let it sit out in a humid environment, the soap will collect water from the room and little droplets of glycerin dew will cover your soap. Humidity is the number 1 cause of glycerin dew on your melt and pour soap.
How can soap sweating be prevented in M&P?
The best way to prevent your soap from sweating is to wrap it in plastic wrap or shrink wrap once you remove the soap from the mold. You can also store your soap in airtight containers to help to prevent sweat on your soap. In the airtight container you could add silica packets or uncooked rice in a satchel to help absorb any humidity in the container so it stays off your soap! Reducing humidity is the key to preventing soap sweat
Another very helpful tip is to start with the right soap base. Some soap bases are much less susceptible to glycerin dew. Look for low sweat or an ‘LCP’ (like cold process) base. I find that bases by the manufacturer SFIC tend to sweat much less than others. Also certain types of bases (like clear/transparent ones) sweat more. Click here for Low Sweat soap base (“LCP” sold at Brambleberry, manufactured by SFIC)
If you don’t wrap or seal up your unmolded soap, store it in a cool dry environment. Keep a dehumidifyer in your soaping area. Keep the room temperature constant as you make your soap, let it harden, remove from the mold, and store because changes in temperature can affect humidity. Let your soap cool slowly and naturally rather than putting the soap in the freezer to unmold. When you pull the soap out of the freezer the cool temperature will attract water in the air just as an ice cold beverage glass does.
How does sweat on soap affect it’s properties?
Soap Sweat / Glycerin dew doesn’t affect your soap’s ability to clean. It just happens when your soap is in a humid environment – it’s doing the job it’s intended – attracting moisture! The only real effect is the appearance of your soap. Hopefully you can prevent glycerin dew with the strategies listed above but, soap sweat may still show up.
How to fix or remove glycerin dew
If you found this article because this has already happened to your soap, you are probably looking for a solution to soap sweating. To get rid of soap sweat, you could try remelting your soap in the microwave or double boiler (be sure not to over heat), and pour it back into molds again. This time around, make sure to keep soap in a dry environment. Otherwise you would just let your soap dry out a bit, but it will have a texture on the surface left over from the glycerin dew.
Do you have any other tips or a related story? Comment below and share!