The addition of cornstarch to Egg Drop Soup is a specific American method of making the soup thicker. In theory, yes, you can leave out the cornstarch if you follow a gluten-free diet; however, it is a personal preference. The addition of cornstarch to Egg Drop Soup offers the following benefits: It makes the soup thicker. Cornstarch is not a thickener, but it gives your food a rich mouthfeel and creaminess you simply can't get otherwise. Makes silky egg flowers. Cornstarch prevents protein bonds from forming in the eggs, making them rubbery rather than smooth and tender.