What key ingredient is typically used to add spice to Kung Pao Chicken?

The key ingredient that typically adds spice to Kung Pao Chicken is dried red chilies. These chilies are a crucial part of the dish, providing the signature heat and flavor that characterize authentic Kung Pao Chicken. The chilies are often stir-fried with the other ingredients, releasing their oils and infusing the dish with a moderate level of spiciness that is balanced by the sweetness of other components, such as the sauce made with soy sauce, sugar, and vinegar.

In contrast, while other options like dried red berries, black pepper, and fresh ginger add various flavors to Chinese cuisine, they do not specifically contribute the traditional spiciness expected in Kung Pao Chicken. Dried red berries might refer to an ingredient that is sweet rather than spicy; black pepper offers a different flavor profile that is more pungent than hot; and fresh ginger, while aromatic and warming, does not provide the same level of heat as dried red chilies do. Therefore, dried red chilies are the authentic choice for achieving the desired spiciness in this popular dish.