If you haven't heard of guar gum, it's a thickening agent that you can use for a wide variety of cooking applications. It's far more powerful than cornstarch or flour for thickening, and it doesn't have to get hot to thicken, so you can use it in cold salad dressings or other sauces very successfully.
You can find guar gum at many specialty food stores or health food stores, and it usually comes in powder form that you can sprinkle into your recipes quickly and easily. It can clump or become gummy if you add too much, so remember to sprinkle just a bit of it gradually throughout the food and stir thoroughly after you add it.
It's important to remember how much to use, because guar gum is quite powerful and quick-acting. If you're substituting for cornstarch in a recipe, use an eighth of what the recipe calls for. For example, if your recipe calls for 1 Tablespoon of cornstarch, use one sixteenth of a teaspoon of guar gum, and if it calls for half a cup of cornstarch, use 3 teaspoons of guar gum. When you use flour, the measurements are different. If you need 2 tablespoons of flour, substitute 3/8 teaspoon of guar gum, instead. If you need 1/4 cup flour, substitute 3/4 teaspoon of guar gum. You can always add a bit more if you're not happy with the thickness, but if you add too much, you can gum up the recipe.
Guar gum is great to use in cold recipes, and it's tasteless, especially in the small amounts you use, so it won't change the flavor of your recipe. It's perfect for people on a gluten-free diet, because you can use it in recipes to act as a binder instead of flour or cornstarch. It's gluten free, and it's easy to add to gluten-free recipes and baked goods. A good rule of thumb is to use 1/2 teaspoon of guar gum per cut of gluten-free flour in the recipe for cakes. For example, if your recipe calls for 2 cups of flour, use 1 teaspoon of guar gum. For cookies, use 1 1/2 teaspoons per cup of flour, and for breads, use 1 teaspoon of guar gum per cup of flour.
Guar gum is also good for people on low-carb diets, because it is extremely low-carb, especially in the amounts used in cooking, and it's tasteless, so it won't affect the taste of the recipes. Low-carb dieters can use it in place of flour or cornstarch to thicken soups, stews, and sauces, and it is often available in low-carb sections of the grocery store, or in special low-carb stores.