Lemon curd: gentle heat
Lemon curd thickens because yolk proteins heat up and link into a loose gel that holds the juice and sugar. Push the heat too hard and the proteins tighten into clumps that squeeze water out, leaving scrambled bits in thin liquid.
Gentle heat and the spoon test
A bowl set over barely simmering water heats more gently than a pan on a flame, which gives you time to react. Keep whisking, and pull the curd off the heat once it coats the back of a spoon. It thickens a little more as it cools.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Why cook lemon curd over gentle heat and keep stirring?
Fast heat clumps the yolk proteins. Rapid heat makes proteins tighten unevenly, giving a grainy or scrambled texture.
True or false: Straining lemon curd removes little bits of overcooked egg and zest, leaving a smoother texture.
True. A fine sieve catches tiny cooked egg bits and zest for a silkier curd.
What went wrong? You crank the heat to hurry the curd along. It ends up as lumpy bits floating in thin liquid.
The fast heat set the yolks into clumps. Proteins tightened too fast and pushed out liquid instead of forming a gel.
Fill the blank: Lemon curd is ready to come off the heat when it ___ the back of a spoon.
Lemon curd is ready to come off the heat when it coats the back of a spoon. A visible layer that stays when you draw a line shows it has thickened.
Your finished curd has a few grainy bits. What is the best rescue?
Push it through a fine sieve. A sieve catches the cooked bits and lets the smooth curd through.