Is there a substitute for flour or starch as a thickening agent?
Flour is often used for thickening gravies, gumbos, and stews. It must be cooked in thoroughly to avoid the taint of uncooked flour. Roux, a mixture of flour and fat, made into a paste before the liquid is added, is used for gravies, sauces and stews. Cereal grains (oatmeal, couscous, farina, etc.) are used to thicken soups. Yogurt is popular in Eastern Europe and Middle East for thickening soups. Soups can also be thickened by adding grated starchy vegetables before cooking, though these will add their own flavour. Tomato puree also adds thickness as well as flavour. Egg yolks have rich flavor and offer a velvety smooth texture but can prove to be difficult to use. Pectin is used as a gelling agent for jams and jellies. Other thickeners used by cooks are nuts or glaces made of meat or fish. For acidic foods, arrowroot is a better choice than cornstarch, which loses thickening potency in acidic mixtures. At (acidic) pH levels below 4.5, guar gum has sharply reduced aqueous solubility,
