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  • QA 121
    Question:
    What, if any, is the difference between 'powder coffee' and 'soluble coffee'?
    Background:
    I have recently read about a coffee factory being opened in Kampala, Uganda, that will process what is called 'powder coffee'. Wondering what type of coffee this is. Kindly advice if there is a difference between 'powder coffee' and what we know to be 'soluble coffee'.
    Asked by:
    Producer Association - Zambia
     
    Answer:

    The brief answer is that there is no difference in the sense that by their nature all types of instant coffee are soluble. Or, all soluble coffee is 'instant' because it offers an instant brew… 

    The term soluble was originally used in the early 1900's to describe the first coffees that were, well, soluble*. However, these were quite expensive and the concept did not reach 'critical mass' until the introduction of the spray drier. Spray drying requires a large cylindrical tower with a conical base. Concentrated coffee liquor is introduced into the top under pressure, with a jet of hot air. The falling droplets dry into a fine powder that cools as it descends. This produces a free-flowing coffee powder of a consistent density, allowing consumers to measure it out correctly 'spoon by spoon'. Instant or powder coffee was part of the staple rations provided to US forces during World War Two and as a result became widely known.

    Further improvement came with the introduction of the agglomeration process that basically wets the powder particles in low-pressure steam, allowing them to stick together. The wet granules are then dried as they descend through a second tower, and are sifted to provide a uniform final granule size.

    Yet more change came with freeze-drying, a process that freezes concentrated coffee liquor (see topic box 02.10.04). After the freezing operation the water is eliminated by gentle evaporation under vacuum and the remaining cake is subsequently broken into small particles. This is gentler on the product and is therefore used for the finer tasting and more expensive blends of instant coffee that are always presented in agglomerated form. The key to freeze-drying is "sublimation". This is where solid ice is changed to vapor without passing through the normal liquid form by applying small amounts of heat while in a vacuum. The fact that only small amounts of heat are used protects the volatile flavors of coffee from burning off.

    It is our understanding that the term 'soluble' was introduced on retail packaging to help consumers differentiate between the better looking and easier to handle agglomerated particles, and the original powder coffees. Freeze-dried coffees too are described as 'soluble'.

    We cannot be sure but could imagine that the article you referred to simply used the term 'powder' as a generic term. However, we would mention that fine powder type soluble coffees, non-agglomerated, still exist, either as low cost products or as more sophisticated foaming products, mimicking espresso coffee. Indeed, technical advances in the spray drying process are allowing it to compete more effectively with freeze-dried, basically because the latter process requires more energy and, therefore, is more costly.

    * For those interested in more detail we suggest the book by R J Clarke and R Macrae, Volume Two 'Technology' of the 'Coffee' series published by Elseviers Applied Science, New York. ISBN 1-85166-034-8

    Posted 01 November 2006

    Related chapter(s):
    Related Q & A:
    QA 064, QA 075