Types of Custards
Custards are mixtures of milk and/or cream, sweeteners (sugar, honey), flavorings (vanilla, nutmeg, etc), and eggs or egg yolks. Custards are thickened by the coagulation of egg proteins during cooking. These egg proteins denature when heated and recombine to form a network that sets or coagulates, at the right temperature, to form the solid gel of a custard. All custard dishes are very susceptible to microbial contamination and should be covered and refrigerated as soon as possible after preparation.
Sweet custards are served as desserts in the form of puddings or as fillings for éclairs and pies. Savory (non-sweet) custards are used for dishes such as quiches. A popular quiche made with bacon and Swiss cheese is known as quiche Lorraine. Custards are further distinguished by their preparation method: stirred or baked.
Stirred Custard (Soft Custard or Custard Sauce). The ingredients of this custard are stirred while being heated on the range over low heat or in a double boiler. The mixture retains a smooth, creamy, fluid consistency. Stirred custard is often eaten as a pudding; however, it may provide the base for many frozen desserts, be served as a sauce for cake, fruit, and other desserts, or be used to replace eggnog. The repeated stirring prevents the formation of a gel, so the custard mixture thickens instead of gels.
Baked Custard. Unlike stirred custards, which are prepared with moist heat, baked custards are an example of dry-heat preparation. Both types of custards begin with the same ingredients, but are simply heated differently. Baked custard mixes are poured into ungreased custard cups that are placed in the oven, usually in a water bath (bain marie), where they sit undisturbed and gel during baking. A water bath is made by filling a large, low-side pan with 1 inch of hot water, into which are placed the cups containing the custard mix. The layer of water insulates the cups and prevents the outside of the custard from cooking to completion before the inside has had a chance to coagulate.
The internal temperature of custards should never be allowed to rise above the point of coagulation of the egg-liquid mixtures. Overheating causes the egg proteins to shrink, allowing liquid to be released from the egg and producing a product with a curdled, weepy, porous appearance. Another problem with baked custards is that they tend to have a runny texture, which makes then unsuitable for making solid pie fillings. As a result, custards to be used as pie fillings are often thickened with starch in the form of cornstarch or flour.
Custards should be baked at 350oF(177oC) until a knife inserted in the middle of the cup comes out clean - about 23 to 25 minutes for custard cups and 35 to 40 minutes for a casserole-size dish. Just before complete doneness is reached, the custard is immediately removed from the oven and placed on a rack. Some additional cooking will inevitably occur during cooling, but can be minimized by using a cooling rack. Should the custard be overcooked, the cups can be set in ice water to stop further coagulation. Undercooking should likewise be avoided, because it will prevent the custard from setting properly.
