Fact of the week: Freeze drying

The freezing part is self explanatory. You take food or drinks and then you freeze it. 

So what is the drying part?

You reduce the pressure of the container and then you apply heat. The ice will sublime and the water vapour is extracted with the reduced pressure.

For instant coffee, it means that the mixture was not heated until all the water had evaporated. Btw, the mixture is sprayed (aerosol or atomized) into a hot chamber where the droplets are exposed to heat. There are collectors at the bottom collecting the residue.