Why does sugar not turn blue-black with iodine solution?

Sugar does not turn blue-black with iodine solution because it does not contain starch or amylose, the starch component that reacts with iodine. Simple sugars such as glucose and sucrose have a different chemical structure and cannot form the blue-black starch-iodine complex.

As a result, when iodine solution is added to sugar, it remains brown or yellow-brown, indicating that starch is absent. This difference helps distinguish starch-containing foods from foods that contain only simple sugars.