What is trace?
Short answer
Trace is the point where the emulsified soap batter thickens. The book works with three stages: just emulsified, thin trace and medium trace.
Explanation
Just emulsified is thin and fluid like cream, with no oil streaks; that's the moment to divide a batch for layers or colors. Thin trace is like thin pudding. Medium trace is like warm pudding or cake batter that holds a drizzle on the surface. Fragrance, post-trace oils and most additives go in at thin to medium trace.
In butter-rich recipes, shea and mango can solidify when they meet cooler lye and fake a thick batter (false trace). That's why the Rosemary & Citrus bar is soaped at a warmer 43–46 °C.
What to do
- Use the stick blender in short bursts. For slow recipes like Castile, blend 20–30 seconds, rest, and repeat for 5–10 minutes.
- Stop at thin trace when working with fast-moving recipes.
Source: The Big Book of Homemade Soap — Recipe chapters, e.g. Castile Soap and Four Spices Layered Exfoliating Bar