What does an egg yolk do in lemon curd?

An egg yolk is an essential ingredient in lemon curd, playing several crucial roles in its texture, flavour, and overall composition:

- Thickening Agent: The egg yolk acts as a thickening agent, helping to create the characteristic creamy and smooth texture of lemon curd. When heated gently, the proteins in the egg yolk coagulate and form a network that traps the liquid, giving the curd its desired consistency.

- Emulsifier: The egg yolk acts as an emulsifier, helping to blend the fat (from the butter) and the water (from the lemon juice) into a stable mixture. Emulsifiers are substances that allow two immiscible liquids to mix and form a uniform dispersion. In the case of lemon curd, the egg yolk helps to keep the butter and the lemon juice from separating, resulting in a smooth and homogeneous curd.

- Richness and Flavour: Egg yolks contribute to the richness and flavour of lemon curd. They provide a source of fat and protein, adding depth and creaminess to the curd. The egg yolks also enhance the flavour by adding a slightly sweet and custard-like note.

- Colour: The egg yolks give lemon curd its vibrant yellow colour. The natural yellow pigment present in the egg yolks combines with the colour of the lemon juice, creating the signature yellow hue of lemon curd.

Overall, the egg yolk plays a vital role in the texture, flavour, and appearance of lemon curd, making it an indispensable ingredient in this delicious and versatile spread.