Spray Dried ProcessThe manufacture of instant coffee begins with brewing coffee in highly efficient extraction equipment. Hot water is passed through a series of five to eight columns of ground coffee beans. The water first passes through several "hot" cells (284-356°F), at least some of which operate at higher-than-atmospheric pressure, for extraction of difficult components like carbohydrates. It then passes through two or more "cold" cells (about 212°F) for extraction of the more flavorful elements. The extract is passed through a heat exchanger to cool it to about 40°F. By the end of this cycle, the coffee extract contains 20-30% solids.
After a filtering step, the brewed coffee is treated in one of several ways to increase its concentration. The goal is to create an extract that is about 40% solids. In some cases, the liquid is processed in a centrifuge to separate out the lighter water from the heavier coffee extract. Another technique is to remove water by evaporation before cooling the hot, brewed extract. A third alternative is to cool the extract enough to freeze water, and then mechanically separate the ice crystals from the coffee concentrate.
Cooled, clarified liquid concentrate is sprayed through a nozzle at the top of a drying tower. The tower is at least 75 ft tall. Air that has been heated to about 480°F is blown downward through the mist to evaporate the water. The air is diverted out of the tower near the bottom, and it is filtered to remove fine particles, which can be recirculated back through the tower or reintroduced during the agglomeration step. The dry coffee powder collects in the bottom of the tower before being discharged for further processing. The resulting powder contains 2-4% moisture and consists of free-flowing, non-dusty particles.
Optionally, spray drying could be followed by a step to form the powder into coarser particles that will dissolve more completely in the consumer's cup. The agglomeration process basically involves rewetting the surfaces of the coffee powder particles and bringing the particles into contact, so that they will adhere to each other and form larger, more granular particles. This is accomplished by exposing the powder to steam or a fine mist, while tumbling it in the air.
Source: http://www.madehow.com/Volume-3/Instant-Coffee.html#ixzz10I2OdBOQ