Coffee dissolves in water, but the extent of coffee solubility varies. Ground coffee beans do not completely dissolve in hot water, while instant coffee, otherwise called soluble coffee, does.
According to CoffeeChemistry.com, a typical coffee bean is composed of 28 percent organic, water-soluble material and 72 percent insoluble cellulose. When hot water is added, as in brewing or boiling, only the soluble material is completely dissolved, giving the solution its distinct coffee flavor and aroma.
Instant coffee is made from coffee beans that have undergone a process of roasting, grinding, extraction and freeze-drying or spray-drying. The process alters the composition and property of the coffee beans so that the resulting product, instant coffee, can dissolve completely and instantly in hot water.