Types of Instant Coffee
These are some of the different methods used to make instant coffee
Freeze drying
The removal of water from the coffee powder via a method known as sublimation. Freeze drying has grown in
popularity to become a common method. Although it is sometimes more expensive it generally results in a higher
quality product. These are the steps which are involved in the freeze drying process.
- Agglomerated wet coffee granules are rapidly frozen (slow freezing leads to large ice crystals and a porous
product and can also affect the colour of the coffee granules).
- Frozen coffee is placed in the drying chamber, often on metal trays.
- A vacuum is created within the chamber. The strength of the vacuum is critical in the speed of the drying
and therefore the quality of the product. Care must be taken to produce a vacuum of suitable strength.
- The drying chamber is warmed, most commonly by radiation but conduction is used in some plants and
convection has been proposed in some small pilot plants. A possible problem with convection is uneven drying
rates within the chamber, which would give an inferior product.
- Condensation - the previously frozen water in the coffee granules expands to ten times its previous volume.
The removal of this water vapour from the chamber is vitally important, making the condenser the most critical
and expensive component in a freeze drying plant.
- The freeze dried granules are removed from the chamber and packaged.
Spray drying
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Spray drying produces spherical particles about 300 micrometres (0.012 in) size with a density
of 0.22 g/cm³ (ref 2). To achieve this, nozzle atomization is used. Various ways of nozzle
atomization can be used each having its own advantages and disadvantages. High speed rotating
wheels operating at speeds of about 20,000 rpm are able to process up to 60,000 pounds (27 tonnes)
of solution per hour (ref 3). The use of spray wheels requires that the drying towers have a wide
radius to avoid the atomized droplets collecting onto the drying chamber walls.
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- Completed in 5–30 seconds (dependent on factors such as heat, size of particle, and diameter of
chamber).
- Moisture content change: IN = 75-85% OUT = 3-3.5%
- Air temperature: IN = 270°C OUT = 110°C
Solvent Decaffeination
Additional moisture is required in the coffee bean in order for solvent decaffeination to function. The method
for introducing this moisture does not matter -- the importance is the water content of the bean, and typically
anything between 18% and 55% is sufficient. The moisture is required to soften the cellular structure of the
bean.
- Basic steps of solvent decaffeination
- Steaming of coffee beans for 30 minutes at 110°C.
- Increase of coffee bean moisture content to above 40%.
- Beans flow through extractor columns with solvent at temperatures between 50 to 120°C. Caffeine is removed
from beans.
- Decaffeinated beans are "steam stripped" of solvent for 90 minutes.
- Decaffeinated beans are removed from extractors and dried.
- Caffeine rich solvent is recycled to be used in step 2.
Water Decaffeination
Water extraction of caffeine was first patented in 1941 by General Foods. Its claimed advantages are:
- Higher extraction rates
- Caffeine recovery by this method produces a purer product
- Less heat treatment of the coffee bean
- No direct solvent contact with the bean
This method takes about 8 hours, considerably longer than solvent decaffeination; however it does seem to
produce a better quality end product.
The basic method involves the use of a water extract of green coffee beans in a battery of columns in contact,
countercurrently, with green beans. As contact is made the green beans preferentially absorb water. The solid
content of the water extract of green beans doubles (from 15% to 30%) as caffeine is taken up. During the 8 hour
process about 98% of the caffeine is removed, which is comparable with the solvent extraction method. The
decaffeinated beans, now 58% moisture by weight, are washed and dried.
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