Freeze-dried coffee is a soluble coffee (instant coffee) product.
How To Make Freeze-Dried Coffee
Freeze-dried coffee is made by first extracting a coffee concentrate from coffee beans under high pressure. This allows the extraction to take place using water which is above the boiling point yet doesn't actually boil.
The Crystallization Process
The next step involves removing the water from the concentrate, and this is done by freezing the concentrate in a vacuum chamber so the water molecules crystallize.
This crystallization results in the separation of the coffee flavoring materials which form into a solid mass. In freeze drying the coffee granules are frozen very quickly to avoid the formation of large ice crystals, the creation of a porous quality, and an undesirable color change.
The Drying Chamber
Next the frozen mass is put into a drying chamber (vacuum chamber), usually on a metal tray, and the chamber is made into a vacuum of sufficient strength to very quickly dry the coffee. The rapidity of drying is very important to insure product quality.
The drying chamber is heated using either radiation (most common), conduction, or convection, which rarely used due to the problem of uneven drying rates deteriorating the quality of the final product.
The Condensation Phase
A condenser is then used to expand the water frozen into the granules, which grow ten times in size as water vapor is removed from the chamber. Following condensation, the granules are packaged for sale.
The temperature of the frozen concentrate in the vacuum chamber is typically raised to just above freezing, yet the concentrate doesn't melt due to the effect of the vacuum. Instead the solid ice becomes a vapor.
This vapor is vented out of the vacuum chamber leaving only the coffee residue. Because the water is removed without using heat, many of the coffee's valuable flavors are preserved.
Now that you know how freeze-dried coffee is made, read about the History of Instant Coffee.
Coffee and Espresso Brewing Tips
For tips on brewing the perfect cup of coffee see our section on Coffee Brewing. You can also read detailed coffee flavor profiles of gourmet coffee and instructions on preparing Espresso Drink Recipes.