Emulsion and trace

The point at which oils and lye have combined and will not separate again, and the moment everything else in the batch is timed from.

Emulsion is the real requirement

What actually matters is emulsion: the mixture is uniform and will not split.

Trace is the visible evidence of it, drizzled batter leaving a mark on the surface, and it is a proxy rather than the thing itself.

A batch at stable emulsion can be poured. Taking it further is a choice about design, not a requirement.

Stages of trace

Emulsion: uniform, still fluid, no separation on standing. Enough to pour.

Light trace: a faint mark that sinks back. The working point for swirls.

Medium trace: pudding-like, holds a mark. Suitable for layers.

Thick trace: holds peaks. Texture on top, and too late for anything poured.

The batch moves through these on its own and faster with heat, with a water discount and with an accelerating fragrance.

False trace

The trap. Hard oils solidifying as the batch cools look exactly like thickening, and the batch has not emulsified at all.

Poured at false trace it separates in the mold, giving an oily layer and a lye-heavy layer, which is both a ruined batch and a caustic one.

Tell them apart by temperature and by behavior: false trace appears while the batch is cooling and it looks grainy rather than creamy. If in doubt, warm gently and blend again.

Blending technique

A stick blender in short bursts, alternating with stirring, rather than running continuously.

Continuous blending traces fast and whips air into the batch, which gives bubbles in the bar.

Tap the blender on the bottom of the container before starting to release the air trapped in the bell, which otherwise goes straight into the soap.

And keep the head fully submerged, for the same reason.

References