Arrowroot starch is a powdered product extracted from the roots of the arrowroot plant. It contains about 23 percent starch. Arrowroot starch is mostly used as a thickening agent in foods like puddings and sauces. Its thickening power is twice that of regular flour. It should be mixed with cold water before adding to a hot liquid to prevent clumping. It's also used in cookies and crackers as a substitute for regular flour and therefore is a good option for those who are gluten intolerant.