It's not practical to combine custard ingredients ahead of time and refrigerate them because most custard recipes require hot milk and immediate cooking. But you can cook custards and chill them until you need them. Custards can be grouped into three basic categories: egg-thickened custards, starch-thickened custards and gelatin-thickened custards. How you prep and cook them varies depending on the type of custard.
Custards: A Primer
Most custards, such as pudding, pastry cream, creme brulee or creme anglaise sauce should be cooked ahead of time and chilled for at least two or three hours before serving them. This chilling time improves the flavor and thickens the custard. You can cover and refrigerate most custards for up to two days before using it in a dessert. Custards contain perishable ingredients, such as eggs and milk, and should be refrigerated within two hours of making them at 40 degrees Fahrenheit. Use them within two days and throw any leftovers. Stir chilled custards, rather than whisking them, which can cause them to break down.
A Good Egg
Egg-thickened custards, such as creme brulee, creme anglaise and a basic ice cream custard, are the most delicate. They thicken at temperatures between 160 and 180 F and should be cooked over a double boiler or in a water bath in the oven. If you overcook them, they may curdle or become grainy or watery. To prevent this problem, use a thermometer and don't cook them beyond 180 F. Stir custards made on the stovetop constantly. Pour custards through a sieve to strain out any bits of egg. Allow the custard to cool before you refrigerate it and seal it tightly with plastic wrap, allowing the wrap to sit directly on the custard so a skin doesn't form.
Starch-based custards, such as pudding and pie filling, get their thickness from cornstarch, flour or tapioca, and sometimes also eggs. You can prep these custards ahead of time, but pay extra attention during the cooking process, especially if you use cornstarch. Eggs contain alpha-amylase, an enzyme that dissolves starch. You must simmer custards containing cornstarch for a minute or two, stirring constantly, to destroy this enzyme. Otherwise, the thickener breaks down during storage, leaving a watery mess. Allow the custard to cool, cover it with plastic wrap and refrigerate it for up to two days. To fix a watery starch-based custard, reheat it and allow it to boil for a minute, or until the custard thickens.
Gelatin is the muscle in the custard world. Its thickening power is strong enough to create firm desserts, such as Bavarian cream or chiffon pie, that can be sliced. In almost every instance, you should prepare and chill these desserts at least a few hours before serving, and up to two days ahead of time. For best results, soften or "bloom" the gelatin in cold water or juice before dissolving it in warm water. Let the gelatin cool and thicken before you beat in egg whites or whipping cream for the most volume. If you're making a pie, bake the pie crust until it's crisp before you add the gelatin custard to prevent sogginess.
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