{Added in 2012: This thread shows that laser diffractometers are not quite sensitive enough to tell the difference between the same grinder making espresso at slightly different doses, or different grinders set to make the shots with the same dose, time and brew ratio. Laser diffractomeerts size particles by measuring the average dimaeter of the shadow they cast. This is too approximate to work for the small size differences in the working range of espresso grinders. However, there's alot of cool graphs for those who are interested}

My apologies for the delay. Kendall finished the laser sizing very quickly; but the results have been head scratchers, so they took a while to analyze.

I am going to put up two posts.

• This first one contains 12 graphs for the 12 grinders submitting samples. Each graph shows the distributions of the two or four samples submitted for that grinder. The title of each graph shows what these are. Glancing at these graphs, you'll see where the hitch lies -- the 18 gram samples aren't always coarser than the 15 gram samples
• The second shows a single analytical graphic displaying the 18 versus 15 gram dose differences for all grinders. Based on this, I discuss the problems with the data and how we intend to proceed.

Please feel free to comment and suggest.

And here it is -- the most complete set of espresso grind distributions ever collected:

Baratza Vario, Single, Basaric


Versalab M3, Single, Basaric


Ascaso I2, Hopper, Campbell


Lelit PL53, Hopper, Cunha


Macap MXK, Single, Leighton


Compak K10, Single, Schulman


Macap M7K, Single & Hopper, Campbell


Compak K10, Single & Hopper, Cobo


Mazzer Kony-E, Single & Hopper, Ivanitzky


Mazzer Robur-E, Hopper two pair, Lampert


Compak K-10, Single & Hopper, Lundgaard


Baratza Vario, Single & Hopper, Lundgaard


Cimbali Junior, Single & Hopper, Wookie

As you can see from the set of graphs, sometimes there appear to be more coarse particles in the finer ground 15 gram samples. What is the source of the problem? Kendall did two sample test/retests and we had two pairs of identical samples submitted by Lampert (thanks!). These test/retest of identical samples allow us to establish a no difference zone. All the anomalous samples fall int this no difference zone. So do some of the samples that are not anomalous. In the end, only five pairs have enough difference between the 15 gram and 18 gram set to be significant, and on all these the 18 gram sample is coarser.

The following graphic shows all the grinder results in one result. To do this, I summarised the distribution data into two parameters - the proportion of coarse particles to fine particles (by volume) and the average size of the coarse particles. The graphic displays the difference between the 18 and 15 gram sample of each pair as a letter a through t.

There are also four red # showing the test/retest difference of identical samples (they have all been put in the upper right quadrant for convenience sake. The circle whose center lies at the intersecting axes and whose diameter passes through the outer points is the no difference zone. !5 of the twenty samples fall in this zone. The five significant samples all show various degrees of either larger coarse particles or a higher proportion of coarse particles. I have placed the legend showing which letter belongs to which grinder below the graphic.


Discussion: Why do fifteen of the samples show no real difference in grind size? Kendall tested and retested samples, and this shows that both he and the machine are operating properly. People submitting no difference samples followed the proper procedure, and set the grinders coarser, there is no change of massive errors on their part, i.e fifteen mislabels or forgetting to set the grinders etc.

There is also no gap in the analysis. The fines do not change in size when the grind is adjusted, and looking at the raw data as counts or areas does not yield anything different either -- the same five pairs show up as different, and the other fifteen as the same, no matter how one looks at them.

This leaves just one hypothesis. The laser sizer isn't all it is cracked up to be. In fact, it usually misses the effect of grind adjustments in the espresso range. How can this be? Here's the theory. Several lasers are used so that each particle casts several shadows. From this, a particle size is computed that is the diameter of a sphere that would cast shadows of equal area. This conversion may not be right when investigating particle packing, since if the particles are not at all spherical, but say flakes, they would pack based on their thinnest dimension, not their average one.

To check this theory, Kendall will test one of the big difference and one or two of the no difference samples on more exotic and far less available equipment (I got the mass production SEM, but there is other stuff beyond my ken). These are capable of giving shape sensitive distribution data. These may show whether the laser sizer muffed the no difference pairs, or whether we are all deluded when we think adjusting our grinders makes a difference.

Good question.

There is a strong positive correlation between mean coarse particle size and the proportion of coarse to fine particles. This is expected: The fines are like bread crumbs, the same size no matter how thin or often you slice the loaf. So if the coarse particles are larger, they were created by fewer breakages of the bean, and therefore also mean less fines. This is why you don't see any grinder points in the off quadrants.

Since all the anomalous sets in the bottom left quadrant are in the zero zone (as are all the hopper/single differences), we can only say that five sample pairs from four grinders (two K10s, one Kony-E and one Cimbali Junior) produced definitively different sized samples for 15 and 18 grams.

But this is impossible -- all the samples pairs have to be different, otherwise the grinders they came from don't work. This means the laser sizers don't have enough resolution for the job, and that the data that has been previously published or posted has questionable relevance to grind or grinder quality.

This is an interesting, albeit unilluminating result; since it contradicts the implicit claims in the literature that laser sizers are adequate for analyzing ground coffee and coffee grinders.