The Science of Using Cornstarch in Pastry Creams and Custards

Cornstarch is an essential ingredient in many pastry creams and custards, acting as a thickening agent to create smooth, velvety textures. It plays a critical role in achieving the right consistency in these delicate desserts, offering stability while preventing them from becoming too runny or too firm. To understand how cornstarch works in pastry creams and custards, it’s important to explore its chemical properties, how it interacts with other ingredients, and the techniques used in incorporating it into the recipe.

What is Cornstarch and How Does It Work?

Cornstarch, also known as cornflour in some regions, is a fine, white powder derived from the starchy part of corn kernels. It is predominantly composed of amylose and amylopectin, two types of starch molecules. When cornstarch is mixed with a liquid and heated, these starch molecules undergo a process called gelatinization.

In this process, the starch granules absorb water and swell, causing the liquid to thicken. The result is a smooth, dense texture that gives pastry creams and custards their luxurious consistency. The temperature at which cornstarch activates is typically around 160 to 170°F (71 to 77°C), and it requires the proper technique to achieve the ideal texture without overcooking or undercooking.

Role of Cornstarch in Pastry Creams and Custards

Pastry creams and custards both require a thickening agent to achieve the right consistency. However, their methods of preparation and their final textures are slightly different, and cornstarch plays a crucial role in both.

1. Pastry Cream: Pastry cream (or crème pâtissière) is a rich, custard-like filling often used in tarts, cakes, and pastries. The recipe typically involves a combination of milk, eggs, sugar, and cornstarch. The cornstarch in pastry cream ensures that the mixture thickens sufficiently to hold its shape when used as a filling, but it must also remain smooth and pourable for easy application.

   Cornstarch in pastry cream helps to stabilize the egg-based mixture, preventing it from curdling when it’s heated. It also helps achieve the ideal creamy texture, so the cream is neither too runny nor too stiff. When making pastry cream, it’s important to constantly stir the mixture to prevent lumps from forming as the cornstarch activates.

2. Custards: Custards are generally made with milk, cream, eggs, and sugar, with some variations including cornstarch. Traditional custards, like crème anglaise, rely on eggs for thickening, but when cornstarch is included, it aids in achieving a smoother, silkier texture. For egg-based custards, cornstarch provides extra stability, ensuring the custard does not break or separate when cooking at high temperatures. It also prevents the custard from becoming too runny, giving it a firmer texture that can stand up to baking or being served chilled.

How Cornstarch Affects the Texture of Pastry Cream and Custard

The texture of a pastry cream or custard is one of the key elements of its appeal. A smooth, creamy consistency is desirable, but it’s also important for the dessert to hold its shape without being too firm. Cornstarch is instrumental in achieving this balance.

• Creamy and Silky Texture: The starch molecules in cornstarch form a gel-like structure when cooked, trapping liquid and creating a thickened, smooth mixture. This is especially important in pastry creams, where the texture needs to be dense enough to hold its shape yet smooth enough to flow easily when spread into pastry shells. Cornstarch helps prevent the creation of a grainy texture, which can occur when the starch is not properly integrated.

• Avoiding Lumps: One of the challenges when using cornstarch in pastry cream or custard is avoiding lumps, which can ruin the smoothness of the dessert. To prevent this, the cornstarch should be mixed with a small amount of cold liquid (such as milk or cream) before being added to the hot mixture. This process, called a slurry, ensures that the starch is fully dissolved and evenly distributed before it’s exposed to heat.

• Setting the Cream or Custard: The starch molecules continue to absorb liquid as they heat up, thickening the mixture and helping it set. In the case of pastry cream, the thickened mixture is often chilled, where it continues to firm up and reach the ideal consistency for filling pastries. For custards, cornstarch provides additional structure, helping it to hold its shape when poured into molds or baked.

Cornstarch vs. Other Thickeners

While cornstarch is commonly used in pastry creams and custards, it is not the only thickening agent available. Several alternatives, including flour, egg yolks, and gelatin, can also be used. Each thickener has distinct properties that can affect the final texture and stability of the dessert.

• Flour: Flour is another common thickener used in custards and creams, but it can leave a slightly different texture compared to cornstarch. Flour thickeners tend to create a more opaque, heavier texture and may not provide the same silky finish as cornstarch.

• Egg Yolks: Egg yolks are often used as the primary thickening agent in traditional custards. They create a rich, smooth texture and provide natural emulsification, resulting in a velvety consistency. However, egg yolks can sometimes be tricky to handle, as they may curdle if heated too quickly or at too high a temperature. Cornstarch, in contrast, provides a more stable structure and is easier to control in the cooking process.

• Gelatin: Gelatin is sometimes used in custards or creams that require setting without additional cooking, such as in no-bake cheesecakes or mousse-like desserts. However, gelatin works differently from starches and doesn’t provide the same creamy, custard-like texture as cornstarch does.

Techniques for Using Cornstarch in Pastry Creams and Custards

To get the best results when using cornstarch in pastry creams and custards, certain techniques should be followed:

1. Make a Slurry: As mentioned earlier, mixing cornstarch with a cold liquid (such as milk or water) before adding it to the hot mixture helps prevent lumps. This process allows the starch to dissolve evenly and be incorporated smoothly.

2. Gradual Heating: When making pastry cream or custard, it’s important to heat the mixture gradually. Rapid heating can cause the starch to gelatinize unevenly, leading to lumps or a grainy texture. Stir the mixture constantly as it heats to ensure even thickening and prevent scorching.

3. Tempering: When adding hot liquid to egg yolks in custard recipes, it’s essential to temper the eggs to prevent them from curdling. Gradually add a small amount of hot liquid to the egg mixture while whisking vigorously, then slowly combine the two mixtures. This technique helps avoid sudden temperature changes that could cause the eggs to scramble.

4. Cooling and Resting: After the custard or pastry cream has thickened, it should be allowed to cool before being used in desserts. Cornstarch thickened creams often benefit from a resting period to fully set and develop the ideal texture.

Conclusion

Cornstarch is an indispensable ingredient in pastry creams and custards, providing the necessary thickening and stability for these delicate desserts. It enhances the texture, ensuring the mixture is smooth and creamy while allowing it to hold its shape. By understanding how cornstarch works and applying the right techniques, home bakers and professionals alike can create perfect pastry creams and custards every time, achieving that ideal balance of texture, flavor, and consistency.