Baked custards set because egg proteins coagulate into a network that traps water and fat. Heating that network too aggressively makes it contract and expel moisture.

What to do in practice

  • Use moderate, even heat.
  • A water bath can buffer rapid temperature change.
  • Remove custards before residual heat pushes them too far.

If it is going wrong, check these first

  • Boiling the custard in the oven
  • Overbaking until completely rigid
  • Whisking excessive air into a mixture meant to bake smooth