What Causes Cracks in Soap? A Beginner’s Guide to Gel Phase

If you’ve ever noticed a crack forming on the top of your cold process soap, you’re likely seeing the first sign of the gel phase in action. Soap cracking often goes hand in hand with gelling, cracks can appear when the soap begins to overheat during this stage. In cold process soapmaking, a partial gel happens when only part of the soap goes through this transformation. Let’s break it down for beginners:

When you make cold process soap, you mix oils (like olive oil or coconut oil) with lye (a strong alkaline solution) and water. After blending, the mixture starts a chemical reaction called saponification, where the oils and lye turn into soap. During this, the mixture heats up naturally because of the reaction.

Sometimes, the soap gets warm enough in the middle of the mold to turn into a thick, jelly-like texture this is called "gelling." But if only part of the soap gets hot enough to gel while other parts (like the edges) stay cooler and don’t, you get a "partial gel." You might see a darker, shinier circle or area in the center of your soap (the gelled part) and a lighter, more opaque ring around the outside (the ungelled part). This can create a funky, uneven look in your finished bars.

Why Does It Happen?

• Temperature differences – If your soap batter, mold, or even your workspace is a bit chilly, only the middle might get warm enough to gel.
• Large molds – Bigger molds trap heat better in the center than at the edges, making partial gel more likely.
• Ingredients – Additives like sugar, honey, milk, or certain oils can cause your soap to heat up more—sometimes unevenly.

Is It a Problem?

Not really! Partial gel doesn’t affect the soap's quality. It’s more of an aesthetic issue. Some soapmakers love the contrast it creates, while others prefer a uniform look.

Tips to Prevent Partial Gel

• Control Temperature: Try to keep both your oils and lye solution between 90–110°F (32–43°C) when combining.
• Insulate Consistently: Wrap your mold evenly in a towel or place it in a warm spot to encourage a full gel.
• Cool It Down:  If you don’t want any gel, put your mold in the fridge or freezer after pouring to keep it cool and stop gelling altogether.

What to Do If It Happens

If you get a partial gel and don’t like the look, it’s still safe to use! You can cut your soap bars in a way that hides the unevenness or just embrace the unique design. It’s all part of the fun of handmade soap!

Want to learn more and get hands-on experience? Join a Wixy Soap Cold Process Method Soap Making Class and discover all the tips, tricks, and techniques to master your soap making journey.