Why did my vanilla or chocolate-scented soap turn brown?
Short answer
Vanillin in the fragrance oil oxidizes in alkaline soap and turns it from beige to deep brown. A vanilla stabilizer slows or prevents it.
Explanation
Vanilla, chocolate, pastry, amber and spice fragrances often contain vanillin. Premix a vanilla stabilizer 1:1 with the fragrance oil (for example 10 ml + 10 ml) and add it at thin to medium trace. Use less stabilizer for low-vanillin fragrances.
Coffee and cocoa give color and texture, but the book notes they leave no lasting coffee or chocolate scent.
What to do
- Check your supplier's vanillin percentage before planning a light-colored design.
Source: The Big Book of Homemade Soap — Fragrances and Colorants for Cold & Hot Process Soap