More on density

May 15th, 2009

I had a brief moment to dig into a couple of books and was pleased to come across the following passage in  Coffee: Recent Developments  that was very kindly sent to me by Jim Schulman.

Maier (1985)1  compared the chemical composition of traditional and fast roasted coffees, using samples of similar roast colour, and found that the water-soluble extract (soluble solids) increased as the roasting time decreased.  The content of specific substances (such as saccharose) changed with the roasting, indicating that chemical compositions of traditional and fast roasted coffee are similar but not identical.  As expected, fine grind of coffee samples led to an increased amount of extract.  Interestingly the difference in the soluble yield between traditional and fast roasted coffee was dimished by fine grinding. This supports the thesis that fast roasted coffee shows increased brew strength due to structural but not chemical changes.

I hope to have some time this weekend to look at a few more things, I just wanted to keep the debate going.  There is some more info on bean swelling that I want to post up too.

Footnotes:
  1. Maier, H.G. (1985) Zur Zusammensetzung kurzzeitgerosteter Kaffees. Lebensmittelchem. Gerichtl. Chem., 39, 25-9 [↩]

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  • http://barismo.com Ben Kaminsky

    Interestingly the difference in the soluble yield between traditional and fast roasted coffee was dimished by fine grinding.


    So just to clarify, the observation here was that fast roasted coffees will have a higher soluble yield at a coarser grind than “traditional” roasted coffees, but that difference decreases as the grind moves towards say, espresso, correct?

    Also, define “fast” and “traditional” or are these simply relative terms?

    • http://www.jimseven.com James Hoffmann

      I only have the summary of the paper, not the paper itself so I don’t know how fine their fine grind is – could be Turkish, could be espresso.

      As for fast roasting – 1 to 2 minutes total would be considered fast, where as 8+ would be considered traditional I think. The 8 is a fuzzier number than the 1-2 of which I am sure.

  • http://www.lux-delux.com/ David Pier

    If you are actually looking for a method of determining the density of a particular batch of roasted beans, I can think of a method. However, it might be more complication or time than you are willing to deal with. My idea:
    1. Pick out a good volumetric piece of glassware, say about 200 ml; this volume will be the variable “VC”.
    2. Zero your scale with glassware.
    3. Fill almost to the measurement line (doesn’t need to be exact as long as it is under the line) with the beans in question and record their mass; this will be the variable “MB”.
    4. Add a fine granular material, about 60-90 mesh, such as coarse rice flour. Tap the container to ensure that the granular material has filled all voids between the beans, then make sure that the granular material comes right to the volumetric marking.
    5. Put the beans and granular material in a coarse sieve and shake out the granular material into a pan. Pour the retrieved granular material back in to the volumetric container.
    6. Record the volume of the recovered granular material; this is the variable “VG”.
    7. The density of the beans is (MB)/(VC-VG)

  • http://www.transcendcoffee.com Poul Mark

    James, when you refer to 1 – 2 minutes of roasting, are you then referring to some form of flash roasting, where you just nuke it? What kind of application would employ this kind of roasting? I am now confused?

    • http://www.jimseven.com James Hoffmann

      You would need a specific kind of roaster for this – perhaps a centrifugal roaster or similar.

      I will see if I can find some kind of info on HTST roasting online.

  • http://tx-coffee.com Jason Haeger

    This doesn’t really raise any questions for me, personally. It sort of confirms what I already suspected based on repeated observations.

    Isn’t the kind of roaster sort of irrelevant to the point of the quoted content?

    Interesting, for sure, but better to see that there is some logic to my intuition.

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