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  • QA 064
    Question:
    In percentage terms, how much soluble coffee can be extracted from roasted coffee beans?
    Background:
    I am a last year chemical engineering student at the University of Valladolid. I am working on a pre-project related to the extraction of soluble coffee, but I do not know the percentages of solubility in the roasted coffee, right before it enters the extracting machines. If it is not too much of a problem, could you please tell me that figure is?
    Asked by:
    Student - Spain
     
    Answer:

    Although your question is somewhat beyond the scope of this website we can nevertheless advise the following.

    A precise figure is not available because soluble extraction yields are variable in that they are influenced by a number of factors such as:
     

    • Blend composition: the yield from robusta is slightly higher than that from arabica.
    • Roasting conditions: the roasting cycle time, temperature used, degree of roast, etc.
    • Extraction conditions: draw-off, the extraction cycle time, pressure, temperature … 
       

    At normal pressure and at a temperature of not higher than 100°C the maximum extraction yield is roughly 30%. However, an extraction phase at higher temperature and pressure enables also substances that are insoluble below 100°C to be extracted, and so can add 10 to 20% more. Basically therefore, the global extraction yield from roasted coffee is between 40 and 50%.

    The International Coffee Organization in London (ICO - www.ico.org) uses an official conversion factor of 2.6 between green coffee and soluble coffee. This coefficient is used for statistical reasons and is an average value, also giving an extraction yield of between 40 and 50% depending on the roasting loss green coffee suffers during roasting. The European Union uses a yield factor of 40% for customs purposes.

    For more on extraction processes, substances and yields we would refer you to Chapter 5 of 'Coffee Technology' by R J Clarke and R Macrae - Elseviers Applied Science - ISBN 1-85166-034-8.  The Association Scientifique Internationale du Café - ASIC (www.asic-café.org) publishes scientific papers on many coffee science subjects whereas one of the leading manufacturers of spray and freeze drying equipment, Niro A/S, is at www.niro.com.

    Other potential sources of information include AFCASOLE, the Association of Soluble Coffee Manufacturers of the European Union (afcasole@coffee-associations.org) and of course the Spanish Coffee Federation (secretaria@tostadorescafe.com).

    Posted 19 December 2005.

     

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