13th April 2013: Grounds


Lovely, beautiful, clean, even grounds…


But where’s the dust? (There’s always dust, after all) Ah! There it is (a little):


Predictably, the Tanzania for my home coarse grinding (whilst being really quite something, naturally), is raising as many questions as answers. One direction that I find it leading me towards (contrary to what one might expect) is to consider investigating various aspects of sieving in more depth. But it’s a pretty deep rabbit hole to go down, especially as there are now already so many other newly designed avenues to explore with simple brewing alone. But it is tempting. After all, how else can one know certain things for sure?! Hence, I am trying very hard to not justify ‘investing’ in the next coffee gadget (an inevitability?). It seems that Compulsive Coffee Upgraditis will always find a way; even when you have already upgraded as far as one can go, there are always interesting tangents and diversions where it can find the path of least resistance. …Oh! And there is that other important measuring device I should really think about saving for as well!


It turns out that it might be possible to quell at least part of this latest urge for more coffee gadgetry, and have at least some of the questions that I have answered without going too deeply down the sieving route. This is one of the wonderful and surprising benefits that can materialise when one of your very BEST customers is also a scientist, who has access to a pharmacy lab with laser particle sizing equipment. This really makes my month!! So in terms of analysing the size(s) and distribution of particles within grind samples at certain (coarse) settings from certain grinders, this could satisfy some of my curiosity. And, far more accurately than sieving would. Actual brewing with separated or otherwise manipulated grounds would however, obviously still require those sieves… And I might still require them to do any extensive, repeated, multiple analyses at home, as potentially it would be really interesting to see the effects on the shape of the distribution curves caused by different bean types and densities, roasts, and different levels of freshness, at the same, and multiple, and recalibrated settings, and also the effects of small single doses popcorning vs larger amounts in the hopper – meaning numerous samples – many more than would be viable or polite through my contact! Like I said – a pretty deep rabbit hole. If I had all the time and gadgetry in the world, it would be great though (I think I’ve said before that the coffee world could do with a millionaire enthusiast with time on their hands to conduct all this sort of research – just imagine!). Although, having said that, much work has already been undertaken, and documented, by the coffee community regarding these topics (and there are various thoughts as to the relevance of fines, and/or any benefits regarding their removal, for brewed coffee), and there are those who understand the findings and the science much better than I could ever hope to.

I think the analysis will probably be Laser Diffraction based on Equivalent Spherical Diameter of particles, as it’s the range of roughly 0-1500 microns/um/micrometers that I’m interested in for my coffee grind samples. The sample/s from the grinder/s I am interested in testing might be a mixture of Mono or Unimodal (for the Tanzania), and potentially some Bi or even Multimodal grind profiles for the other grinder or two, all being ‘polydisperse’, naturally, and all measured on this same volume diameter/ESD basis. Laser diffraction is more accurate than sieves for a number of reasons. However, there is also still a degree of inaccuracy involved with expressing (assuming) the size of irregular particles in terms of ESD – because they are not spherical. The scattering of light from an irregular particle is not the same as from a sphere, even one of a similar volume. And also, in brewing terms, irregular shaped particles will not extract in the same way, or at the same rate, as a spherical or similarly uniformly shaped particle. Some laser diffraction measurement systems however, are equipped with an irregular particle analysis mode, which counteracts the inaccuracies when measuring irregular particles like coffee grounds.

This should theoretically provide data, and sizing, and graphs, which are more accurate to the actual individual particles within the sample. Quite how the irregular shapes are assessed for their size in this way, or how successfully the compensated irregular sizing analysis distinguishes the actual size and shape of the irregular particles, and how well it therefore correlates to the way that the irregularly shaped coffee ground particles actually extract, I am not sure. For instance, from what I understand, a fairly flat-shaped coffee particle that is 1800 microns wide, but only 600 microns thick, will extract in roughly the same time frame that a 600×600 micron diameter coffee particle with a much smaller total volume (more cube or spherically shaped for example) will extract in. Admittedly three 600x600x600 um coffee particles would probably extract a bit faster than the single 600x600x1800 um particle, due to their larger surface area. But nonetheless, the extraction rate of the 600×1800 particle would still be related more to its lowest measurement than its highest – the extraction rate of a particle is essentially defined by its smallest diameter (although admittedly the reality is more complex than this – coffee grind particles are utterly ‘organic’ in shape, and each will usually have a whole multitude of varying measurements, which will affect its extraction in incomprehensibly complex ways…! But, you could still attempt to generalise the basic shape and dimensions of an irregularly shaped coffee particle, to anticipate its general extraction characteristics and extraction rate). And therefore, hopefully this compensating irregular particle analysis mode would read that larger particle as something like 600 microns, not 1800 or anywhere near that. Whereas the ESD system might read it as a larger measurement. (This issue of individual particles is of course very different to the rate/way in which a whole coffee grind sample extracts, as that contains a population of many different sizes, and perhaps shapes.)

I don’t know yet whether the laser system analysing my own sample/s has this feature nor not, but either way, it will still provide a much more accurate measurement than the sieves.

Apparently some laser diffraction systems are also capable of measuring particles smaller than a micron – down to nanometers. Whereas measurement of particles smaller than nanometers (sub-nanometer) would require something like a Dynamic Light Scattering measurement system, or ultra microscopes – but fortunately this is not necessary for my purposes where coffee grounds are concerned. The fines occupy (as far as I know) the 0-150 um region, roughly (depending on your definition), with the rest of the general grind population, depending on the setting, going up to as much as 1.5-2mm at the coarsest press settings (1500-2000 um), with some particles (at their widest points) even going as high as 3-4mm (3000-4000 um), but with most particles usually occupying the 500-1500 um range for most filter and press purposes – and normal Laser Diffraction sizing is ideally suitable for this range. What it might be able to tell me about the shape of the particles, if anything (and what it would mean), I’m not so sure (casually, for instance, I have observed that the largest Tanzania particles at the coarsest settings are often quite wide and flat in shape (flake-like), meaning they would extract faster than their widest diameter/sieve mesh size might suggest).

But what I’m most interested in for now is simply confirming the size in microns at certain varied grind settings, and the % distribution/spread of sizes within the sample. Fascinating and exciting!

Please excuse any cack handed, poorly informed, misinterpretation of any of the science/equipment terms, some of which I have gleaned rather rapidly this evening whilst looking into some aspects of this topic a bit further than before!

Naturally, I’m aware of those fascinating Marco/Ditting/Mahlkonig filter profile graphs that are out there (and the HB Titan Grinder Project espresso profile graphs). But the data is limited, and not necessarily precisely specific to my own grinder/s.


2 Responses to “13th April 2013: Grounds”

  1. Mukhtar Says:

    Hi Trevor,

    I’m glad you brought up the topic of grounds and consistency. I’ve been using a Hario Mini Mill as of recent and whilst I can get a pretty consistent grind if I’m grinding quite to a filter consistency for using in an Aeropress, every once in a while when I fancy a french press, I find that a coarses grind yields much more ‘dust’ which leads me to believe that the cup I am drinking is too ‘sludgy’ and over extracted…? Please shed some light on this matter… I don’t think I have ever seen anything as consistent as those photo’s out of my mill, after all it is a ~£20 device compared to… let’s not mention how much you spent on your machine :).


  2. thebeanvagrant Says:

    Hi Mukhtar,

    Firstly, the grounds in the photos are from a coarse setting on my Tanzania, but it is one sample that has been separated with sieves (one sieve at about 400 microns which separated that small amount of fines/dust out, and one larger sieve at maybe 650-800 microns which separated those coarser particles from the medium sized ones). So don’t worry – that stuff’s not stright from the grinder! NO grinder is capable of delivering completely fines-free grounds, the physics of bean breaking just don’t allow for it.

    That said, different grinders will produce different amounts of fines, and different distributions of various sizes. The Tanzania is one that tends to give a much more uniform grind at medium to coarse settings – but there’s still a population of different sizes, and a % of fines within each grind sample.

    And there are differences of opinion about whether or not it’s actually a good thing to have 0 fines anyway.

    It might well be that your Hario produces a more even, uniform grind at a more medium setting, and more fines at a coarser setting. But it might just be easier to perceive the fine particles amongst the coarser ones – there might still be a similar level of fines and variance (perhaps even more fines) at the finer settings – it just becomes harder to see them.

    Also – your Aeropress will naturally deliver a cleaner cup due to the fine paper filter. Whereas FP will always be more sludgey, as the filter is coarser, and allows more fine particles and sediment through.
    That said, there are many various techniques for FP – some of which can reduce the amount of sludge, and improve the brew.
    And, many people actually prefer (or appreciate equally, just in a different way) FP over more filtered brew methods – becuase of the greater body you get with it, and because the full immersion method of FP, together with that wider, metal filter which lets more flavours and oils through, can actaully give a more complex and sincere representation of the coffee in some ways – much like the Cupping process used to professionally taste and assess coffee.

    With all methods, you might well have your preferences, but you might also find that playing and experimenting with all the parameters, and persevering with each method some more, will end up giving you great results that you hadn’t originally expected.

    Your grinder might not give the very best results, but it’s probably fine for starters at least, and way better than a blade grinder! 🙂

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