Adding which ingredient is essential for flavoring Chow Mein?

Adding soy sauce is essential for flavoring Chow Mein because it provides the savory umami taste that defines this dish. Soy sauce is a fermented product made from soybeans, wheat, salt, and a fermentation starter. Its rich, salty flavor enhances the overall taste of Chow Mein, balancing the noodles, vegetables, and any protein that might be included. The depth of flavor that soy sauce contributes is vital to achieving the authentic flavors typically associated with Chinese stir-fried dishes like Chow Mein.

In contrast, while vinegar can add acidity and brightness to certain dishes, it is not a traditional element in Chow Mein. Water is used primarily for cooking and steaming, but it lacks flavor and wouldn't be used for seasoning. Pork broth might add richness if used, but it's not a common or essential ingredient for Chow Mein itself. Soy sauce, therefore, stands out as the key ingredient necessary for imparting the characteristic flavor that defines this popular dish.