Starch

Starch increases the temperature of egg coagulation by interfering with the process. To understand how effective starch is at slowing the process and increasing the temperature of egg coagulation, compare the cooking of pastry cream with that of vanilla custard sauce. Pastry cream is essentially custard sauce with added cornstarch or flour. Pastry cream is—must be—brought to a boil and boiled for 2 or more minutes. Vanilla custard sauce could not survive 2 minutes of boiling. In fact, custard sauce generally curdles before it reaches 185°F (85°C). While other differences between the two formulas exist, the main reason pastry cream can be boiled without curdling is because it contains added starch.