What is this dark patch on my soap?

Well, let me explain…

When cold processed soap is blended and poured into the mold to set up, it goes through the saponification process, which is the chemical reaction that changes the raw ingredients into soap. The saponification process takes around 48 hours to complete. Then, it needs to cure for 4-6 weeks to allow excess water to evaporate. Curing creates a firmer bar that lasts longer in the shower.

When starting to make soap, the lye solution can reach temperatures of up to 93 degrees Celsius and so needs time to cool before blending with the melted oils. The melted oils and the lye solution should ideally be within 10 degrees of each other before blending together. I usually soap with my raw ingredients between 27- 40 degrees Celsius. Generally speaking, the cooler you soap, the more time you will have for intricate patterns and swirls.

When saponification is occurring in the mold, the temperature of the raw soap batter will increase, due to the chemical reaction taking place. Some additives to the soap batter can also increase this temperature even further, such as milks, alcohol, sugar, honey and molasses.

Many soapers will freeze their milks before blending into the lye solution to prevent scorching and to maintain the lowest temperature possible. Generally speaking, the hotter a milk soap batter gets, the darker it ends up in colour basically. A lot of soapers and their customers prefer a creamy white goat milk soap. Some add titanium dioxide to keep them white but if you want to keep them more natural, you try to manage the temperatures to control the colour outcome, instead of adding titanium dioxide. Sometimes it is difficult to manage the temperature of the inside of the soap batter in the mold. Managing the temperatures can depend on the temperature of the room you’re working in, the temperature of your raw ingredients when you started soaping and how much of the ingredient you used that accelerates the heat.

When a soap batter is going through saponification and gets to really high temperatures in the soap mold, it goes through a process called the ‘gel phase’ or ‘gelling’. This affects the colour of the soap when it comes out of the mold, the parts of the soap batter that gelled will be darker than the rest of the soap. The soap is the same, pretty much, whether light or dark in colour, it is just based on the preference of the soaper or customer.

Gelling soap can sometimes result in more vivid colours so some soapers actually try to achieve gel on purpose by popping the soap mold on a heating pad, insulating the mold or even popping it into a preheated oven for a while.

Most soapers who want to keep their milk soaps really white will try to prevent the gel phase by keeping the soap batter in the mold as cool as possible. They pop the mold into the freezer or fridge to set up to fight against the natural rise in temperature of the soap batter to maintain that light, creamy colour.

As you can now understand, it can be a very complicated process and my latest batch of goat milk soaps (Dreamy and Creamy unscented (pictured above) and Goatsmilk and lemon myrtle) went through a partial gel so they have some darker and some lighter areas, a bit like an ombre effect, so I just thought that I would explain the reason for this, as unfortunately, people sometimes throw out the soap thinking that it is no good, just based on the colour (even some soapers have wasted soap for this reason).

So, rest assured that if your soap has some darker patches, the reason for this is the soap has gelled, or partially gelled and is purely an aesthetic issue and does not change the effectiveness or benefits of your soap. Let me know, how do you like your milk soaps, creamy white or more of a honey colour?

Have a bubbly day!

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