Lecithin

Lecithin is a group of fat-like molecules called phospholipids that act as natural emulsifiers. It is found in egg yolks, soybeans, sunflower seeds and the cell membranes of most living things, and it is the main reason egg yolk can turn oil and lemon juice into creamy mayonnaise.

What it is made of

The most common lecithin molecule is phosphatidylcholine. Its structure has:

• A phosphate-containing head that is attracted to water.
• Two fatty acid tails that are attracted to fat.

That split personality lets it sit at the boundary between oil and water, coating droplets so they stay suspended in an emulsion.

Where lecithin comes from

• Egg yolk: about 9–10% phospholipids by weight, which is why yolk is the classic emulsifier.
• Soybeans: the main commercial source, extracted from soybean oil.
• Sunflower seeds: a popular soy-free alternative.
• Smaller amounts in milk, liver, peanuts and wheat germ.

What lecithin does in cooking

• Mayonnaise and hollandaise: coats oil or butterfat droplets so the sauce stays thick and glossy.
• Chocolate: around 0.3–0.5% lecithin lowers viscosity so melted chocolate flows better and coats more thinly.
• Bread: softens the crumb and slows staling.
• Foams and "airs": a small amount of powdered lecithin whipped into a flavoured liquid makes light, stable foams.
• Release sprays: prevents food sticking to pans.

Using powdered or liquid lecithin

Start small. For a light foam, about 0.5–1% by weight is plenty (1–2 g per 200 ml of liquid). Blend at the surface with a stick blender to pull in air, then spoon off the foam.

For vinaigrette, about 1 g (¼ tsp) per 250 ml (1 cup) keeps it emulsified much longer than shaking alone.

Heat and lecithin

Lecithin itself tolerates heat well, but in egg-based sauces the yolk proteins don't. Above about 70 °C / 160 °F they set and the sauce curdles, even though the lecithin is still working.