Why it happens
A custard works by holding egg yolk proteins in a narrow temperature band. Heated gently, they unfold and link loosely, trapping the liquid around them and thickening it to a pourable cream. Heated further, they link tightly to each other, squeeze the liquid out, and form solid lumps — which is scrambled egg.
The band between those two states is narrow, roughly ten degrees, and the transition is fast. Worse, the temperature at the bottom of the pan is always higher than the average, so a custard can be curdling at the base while the bulk of it is still fine.
Everything below is about staying inside the band and knowing the moment it is time to stop.
Rescuing it
Speed matters — the first thirty seconds is when this is recoverable.
- Get it off the heat immediately and pour it into a cold bowl. The pan will keep cooking it otherwise.
- Whisk hard, or blitz it with a stick blender for ten to twenty seconds. This physically breaks the curds apart and will often restore something close to smooth.
- Strain it through a fine sieve to catch what is left.
- Add a splash of cold cream or milk while whisking, which drops the temperature and dilutes the curds.
- A teaspoon of cornflour slurry whisked in and briefly reheated will stabilise a marginal custard.
- If it looks like scrambled eggs in milk, it has gone too far. Nothing brings that back.
Making one that does not curdle
- Whisk the yolks and sugar together first, until pale. The sugar physically gets between the proteins and raises the temperature at which they set — this is genuine insurance, not a flourish.
- Heat the milk or cream separately until steaming, not boiling.
- Temper: pour a little of the hot liquid into the yolks while whisking, then a little more, then return the whole lot to the pan. Never pour cold eggs into hot liquid.
- Cook over low heat, stirring constantly with a spatula that reaches the corners of the pan. The base is where it curdles first.
- Watch for the thickening. It happens suddenly. The classic test is that it coats the back of a spoon and holds a line when you draw a finger through.
- Take it off the heat the moment it does, and pour it immediately into a cold bowl. Residual heat in a hot pan will curdle a finished custard in seconds.
- Strain it anyway. It takes ten seconds and catches anything that started to set.
Insurance policies
- Cornflour
- A teaspoon or two per 500ml makes a custard far harder to curdle, because the starch interferes with protein bonding. It is why pastry cream can be boiled and crème anglaise cannot.
- A bain-marie
- A bowl over simmering water cannot exceed 100°C and heats gently. Slower, and much safer.
- A thermometer
- Custard thickens in the region of 80°C and curdles not far above. If you own one, use it.
- A heavy pan
- Thin pans have hot spots, and hot spots are where curdling starts.
- A cold bowl ready
- The most under-rated step. Pouring the finished custard out of the hot pan immediately is what stops it going over at the last moment.
Common questions
Can I fix curdled custard with a blender?
Often, if you catch it early. It shears the curds small enough to be unnoticeable. It will not fix a fully scrambled one.
Why can pastry cream be boiled?
It contains cornflour, which stabilises the eggs. Crème anglaise has no starch, which is why it is so much more fragile.
Does adding cornflour change the taste?
A little — it makes the custard slightly heavier and less silky. For most purposes the trade is worth it.
Can I use a whole egg instead of yolks?
You can, and the white sets at a lower temperature than the yolk, so it curdles more easily and tastes less rich.
Try this next
- Egg the setting range this depends on
- Double cream and why fat stabilises
- Split sauce the same failure in other sauces