Firstly what the end products of the starch converting to glucose are soluble. Starch is converted to alpha glucose monomers by the addition of water to the glycosidic bonds which join the glucose...
If an object/substance has high density, it is most likely insoluble. Insoluble substances are incapable of dissolving in water. This is true for alluminum, copper, gold, silver, iron, tin, platinum,...