Sweating and glycerine dew

Droplets on the surface of a cured bar, which is the failure that makes wrapping a technical decision rather than a presentational one.

Beads on the surface

Clear droplets, sometimes a sticky film, on a bar that was dry a week ago.

It looks like the soap is weeping, and in a sense it is: it is pulling water out of the air.

Why soap attracts water

Saponification produces glycerine, and glycerine is hygroscopic: it draws moisture from the atmosphere.

Handmade soap retains its glycerine, which is one of the things that makes it good and is exactly what causes this.

Commercial bars frequently have it removed, which is why they do not sweat.

When it happens

High humidity, most obviously.

A change in conditions: a bar moving from a dry cure room to a humid shop, or a cold bar warming in a warm room, which condenses moisture on it.

Summer, in most climates.

And inside airtight packaging, which is the important one: a bar sealed in film before it has finished curing sweats inside the wrapper, and the customer opens a wet, slippery bar.

What to do about it

Cure fully before wrapping, confirmed by weight rather than by calendar.

Wrap in something breathable, paper, a cigar band, a box, rather than sealing it, which is why so much handmade soap is wrapped this way rather than shrink-wrapped.

Store and display cool and dry, and away from a bathroom.

And tell the customer how to keep it: on a draining dish, out of the shower stream. A bar left in standing water dissolves, which is the commonest complaint in the craft and is entirely a storage question.

References