What is Soluble Coffee?

Soluble or ‘instant’ coffee was invented in 1901 by Japanese-American chemist Satori Kato of Chicago but was not marketed commercially until 1938. Since then quality and diversity have grown dramatically. Soluble coffee has a number of advantages including speed of preparation, lower shipping weight and volume, long shelf life and being relatively inexpensive.

Soluble coffee is manufactured, just like any other coffee, from ground beans and is commercially prepared by either freeze-drying or spray drying methods. The first stage involves the preparation of a coffee concentrate from which the water is removed, either by heat, known as spray dried, or by freezing, to produce a soluble powder or granules. During the process of dehydration, the coffee essences may be lost, but these are captured and returned to the processed coffee.

Instant coffee is available in powder or granulated formats contained in multiple packaging solutions. The strength of the yielded beverage is determined, by adding more or less powder to the water.  Soluble coffee is a convenient way for preparing iced coffee as it instantly dissolves even in cold water.

Soluble Coffee Production

The green coffee beans are first roasted to bring out their flavor and aromas. Once roasted the beans are then finely ground. Grinding is performed in order to allow the coffee to be put in solution with water for the drying stage.  Once roasted and ground, the coffee is dissolved in water. This stage is called extraction. Hot water is added and this concentrates the coffee solution to about 15–30% coffee by mass. If required this may be further concentrated before the drying process begins by either vacuum evaporation or freeze concentration.

Freeze Drying Soluble Coffee

The principle of freeze drying is the removal of water by sublimation. Although it is sometimes more expensive then Spray Drying, it generally results in a higher-quality product.

1. The ground wet coffee granules are rapidly frozen.
2. Frozen coffee is placed in the drying chamber.
3. A vacuum is created within the chamber.
4. The drying chamber is warmed.
5. The previously condensed frozen water in the coffee granules expands to ten times its previous volume. The removal of this water vapor from the chamber is critical component in the freeze-drying process.
6. The freeze-dried granules are removed from the chamber and ready to be packaged.

Spray Drying

Spray drying is preferred to freeze drying in some cases because of its economy, short drying time, and usefulness when dealing with such a heat-sensitive product and the fine, rounded particles it produces.

Spray drying produces tiny spherical particles by using nozzle atomization through high speed rotating wheels. The use of spray wheels requires that the drying chambers have a wide radius to avoid the atomized droplets collecting onto the drying chamber walls. One drawback with spray drying is that the particles it produces are too fine to be used effectively by the consumer; they must first be either steam-fused or by belt agglomeration to produce particles of suitable size.