What does when set mean baking a pie?

"When set" in the context of baking a pie refers to the desired state of the pie's filling before baking it. The filling is considered "set" when it has thickened and stabilized enough to hold its shape when the pie is cut and served. This is usually achieved by gelatinizing starches, coagulating proteins, or chilling the pie.

Here are the different ways to set a pie filling:

1. Gelatinization: Some pie fillings, such as fruit pies, contain ingredients like flour or cornstarch that act as thickening agents. When these ingredients are mixed with liquid and heated, the starch molecules absorb water and swell up, causing the filling to thicken. This is known as gelatinization. As the pie cools, the gelatinized starches further set and stabilize the filling.

2. Coagulation: Custard pies and other fillings that use dairy products, such as eggs, milk, or cream, rely on coagulation to set. When these dairy ingredients are heated, the proteins in them coagulate and solidify, causing the filling to thicken and become firm. Coagulation is the same process that causes scrambled eggs to set when cooked.

3. Chilling: Chilling is another way to set a pie filling. Some pies, such as cream pies or no-bake pies, do not require baking at all. Instead, the filling is refrigerated or frozen to set. In this case, the cold temperatures cause the filling to solidify and stabilize.

The specific method of setting a pie filling depends on the recipe and the desired texture of the pie. Some fillings may require a combination of techniques, such as thickening with cornstarch and then chilling, to achieve the desired consistency.