When coffee extract is discharged from the extractor, it has a solids
content of 6-8 % TS, depending on how the extraction and aroma recovery is performed.
Concentrate evaporation
To obtain a first class
instant coffee powder, it is necessary to concentrate the extract (without the
aroma fraction). This is typically done in a falling-film evaporator with 2-4 stages to save
energy, either in form of steam in a TVR evaporator or electricity in an MVR
evaporator. In both cases, the evaporator is operated under vacuum at low
temperature. Hereby a very lenient treatment of the extract is obtained and
deterioration of the coffee taste is avoided. In combination with the aroma
recovery system, an excellent concentrate with all the valuable aroma and taste
elements preserved is produced.
If the concentrate is to be spray dried, it is possible to increase the solids content to
approx. 50 % TS. For freeze dried
coffee, the solids content is approx. 45 %.
Freeze concentration
It is also possible to use freeze
concentration where water is removed as ice crystals. This process
operates at temperatures below the freezing point and obviously all the aroma
is maintained.
Membrane filtration
The aroma fraction of the extract
can be preconcentrated when it is discharged from the aroma recovery plant by reverse
osmosis in a membrane filtration system. This slightly changes the taste
profile, which is an advantage for some coffees and in some markets.