A custard is a liquid that is thickened or set by the coagulation of egg protein.
There are two basic kinds of custard:
- Stirred custard is stirred as it cooks and remains pourable when done.
- Baked custard is not stirred and it sets firm.
One basic rule governs the preparation of both custards: Do not heat custards higher than an internal temperature of 185°F (85°C).
This temperature, as you know, is the point at which egg-liquid mixtures coagulate. If they are heated more than this, they are likely to curdle. An overbaked custard becomes watery because the moisture separates from the toughened protein.