Instant coffee soared in popularity in the mid-20th century after becoming a global consumer food product distributed by Nestle. This fast, hot drink was produced entirely from coffee beans using spray drying and freeze drying techniques. You can make your own instant coffee from coffee powder using a simplified version of freeze drying.
Grind the roasted coffee beans into a powder.
Sprinkle the coffee on a metal mesh tray so there is air circulation below and above the coffee at all times.
Remove all items from your freezer. Turn down the temperature as much as possible so that the air can absorb the water in the coffee, or cause it to sublimate. In industrial settings, a vacuum installed in the freezer will complete this process.
Put dry ice in the freezer to aid the process. Allow the coffee to remain in the freezer for at least one week, periodically replacing the dry ice. Dry ice preserves coffee emulsion and aroma.
Remove the coffee from the freezer and immediately seal in a moisture-free, airless container. Achieve this by putting the coffee in a zip-lock bag and using a vacuum hose to suck all of the air out through one small open end of the zipper. Instant coffee is usually packaged in a low-oxygen area, however at home this environmental factor may not be possible to achieve.
Store your homemade instant coffee in a cool, dry place where the airless container cannot be punctured. Reconstitute a teaspoon of coffee with 236ml of hot water and enjoy.
Consider using a French press as an alternative to making your own instant coffee.
Thanks to the industrial vacuums, industrial freezers, oxygen removal to preserve flavour and climate control, commercially available instant coffee products may have higher quality and lower prices than homemade freeze-dried versions.