The real reason eggs are used in custard

Unlike the 17-ingredient, only-grandmasters-of-the-cooking-world-need-apply mole sauce, simple custard only relies on a handful of ingredients. According to Crafty Baking, custard is made up of eggs, cream or milk, sugar, usually salt, and flavorings. Some recipes call for a thickening agent like flour or cornstarch, but the number one thickening agent in custard is eggs. But, how do eggs thicken custard?

Time for a little science: Egg yolks and whites contain proteins that unwind, break apart, and reconnect to form long strands. Liquid gets trapped in the strands, causing the mixture to thicken. The liquid egg becomes firmer as it cooks, becoming semi-gelled or fully gelled when cooled. This consistency gives custard its velvety, smooth texture. Since eggs are key to the structural integrity of custard, it's paramount they are fresh and preferably large Grade A. As far as cooking, low and slow is the way to go.

Keys to custard success

Egg-based custards are usually baked in water baths (a pan of hot water placed in the oven) or a double boiler to prevent overheating. Since cooking eggs to the right consistency can be a little tricky, some custard recipes call for starch. Starch thickeners like flour or cornstarch can help prevent the eggs from overcooking since the starch molecules slow protein coagulation. Custards using starch can even be baked under direct heat, and Crafty Baking recommends cooking the mixture to just below boiling.

Adding sugar to custard can be a matter of finding the sweet spot. Sugar increases the coagulation temperature and time, so sugar should be added while your whisk is moving. However, too much sugar prevents the eggs from coagulating. Flavorings like melted chocolate, vanilla extract, or fruit can up your custard game. Be forewarned, flavorings can also decrease coagulation time, and most should be added after the custard has cooked, but not set. We really like the sound of this caramel custard from Taste of Home; feel free to call us when it's ready.