Sunday, November 11, 2007

When soap goes rogue

Soap making is an art, but it's also a science. At its most basic, soap is made through the chemical reaction between a base and an acid. The fatty acids found in oils create specific properties in the soap, and each fatty acid reacts differently with the sodium hydroxide. The responsible soap maker carefully calculates these reactions and measures the ingredients as accurately as possible. In a perfect environment this would create the perfect soap every time.

However, there are three main variables that can interfere with this chemical reaction. They are heat, humidity, and the homogeneous blending of the ingredients. I will talk about heat and humidity in other articles. It is the importance of proper blending that is occupying my mind at the moment.

In properly blended soap, the sodium hydroxide reacts in its entirety with the fatty acids in the oils. No sodium hydroxide will remain in the final product. Most modern soap makers use stick blenders to achieve this even mixing of the soap ingredients.

Recently, I made a goats milk and oatmeal soap. As it was curing, it continuously wept oil. This is not a good sign! When I took it out of the mold, this is what I saw.

Click to enlarge

In this soap, the ingredients were not mixed homogeneously, allowing pockets of sodium hydroxide to form. Note the uneven colors and the vertical lines between layers. Those vertical lines are sodium hydroxide crystals, leftover due to uneven mixing.

This soap has gone into the trash, and my stick blender has been replaced. I shouldn't see this again for a very long time (knock on wood). However, this experience underscores the importance of testing the pH of every batch of soap. Soap, whether handmade or commercial, should have a pH of 9-10. Any higher, and the soap will be too harsh on the skin; any lower, and the soap won't be able to clean.

If the soap fairy should visit you with a bad batch of soap, remember each one is a learning experience. Put your gloves back on and try again!

Happy soaping!