Mixing your own onion soup mix substitute gives you the opportunity to know exactly what is in your spice blend. With this diy version you can control the salt content, make sure there are no unwanted additives or gluten. A store-bought packet of lipton onion soup mix on the other hand contains a number of unwanted addititves, such as caramel color, yeast extract, soy sauce, high oleic sunflower oil, corn syrup, disodium guanylate or disodium inosinate, for example.