Freeze dried coffee is made by the sublimation of ice.
Freeze-dried coffee differs from ordinary instant coffee in an important way. To make either kind of fast-beverage powder, they first brew two-thousand-pound batches of incredibly strong coffee.
If they are making instant coffee, they then quick-dry this thick brew by dropping it down through a high-temperature chamber. All the water evaporates and only powdered solids reach the bottom. Unfortunately, the heat drives off some of the most flavorful coffee chemicals.
On the other hand, when making freeze-dried coffee, they freeze the strong brew into blocks of solid coffee-ice. Then they pulverize it into granules and put it in a vacuum chamber, where the water molecules are sucked directly out of the ice, by sublimation.
Most connoisseurs of coffee-in-a-hurry believe that, compared with ordinary instant coffee, freeze-dried coffee has a truly sublime flavor.