Lecithin and why it is in your chocolate

Lecithin is a phospholipid emulsifier, usually from soy or sunflower. In chocolate it coats the surfaces of sugar particles, which are hydrophilic and would otherwise resist being wetted by fat.

That coating dramatically reduces viscosity. A fraction of a percent of lecithin does what several percent of additional cocoa butter would do, which is why it is used almost universally in commercial chocolate.

Typical use is 0.3–0.5%, and above about 0.5% it stops helping — the effect saturates and further addition can actually increase viscosity again.

So lecithin is present in genuinely tiny amounts. A bar listing it as the fourth ingredient after cocoa mass, sugar and cocoa butter contains a rounding error's worth of it.

Craft makers frequently exclude it, for two reasons. One is a preference for the shortest possible ingredient list as a statement of intent. The other is that at very high cocoa content the extra cocoa butter is wanted anyway, so lecithin's cost saving is irrelevant.

Neither reason makes lecithin harmful. A two-ingredient bar and a bar with 0.4% lecithin differ in philosophy far more than in anything you can taste.

PGPR — polyglycerol polyricinoleate — is the other common emulsifier, and it works differently: it reduces yield stress rather than plastic viscosity, which matters for moulding thin shells. It is often used alongside lecithin rather than instead of it.

Sunflower lecithin has largely displaced soy in products avoiding soy allergens, and behaves essentially identically.