The industry standard approach for measuring grind size distribution is to use a laser diffractometer. These machines cost hundreds of thousands of dollars, and so they are inaccessible to most coffee roasteries. These machines produce highly replicable results, and they have long been considered the ‘gold standard’ for measuring grind size distributions.
In this video, Matt explains how the machines work
However, as well as being out of reach for all but the largest roasteries and equipment manufacturers, the way these machines work is something of a ‘black box’, according to Professor Abbott. ‘They’re just awful. They’re full of artefacts because you have to dilute the coffee,’ he says. ‘In the actual diluting, who knows what’s happening there?’
The results can’t be examined in the way a simple image analysis can, to ensure that no artefacts or outliers are affecting the results. When using image analysis-based methods such as in these apps, ‘you can see what’s going on, you can see if you’ve mis-sampled, you can see the odd big rocks’, Abbott explains.
Before the development of these apps, the only other option available was to pass the coffee through a set of sieves of different sizes and then weigh the results. While lab-grade sieves are expensive, sieves designed for coffee, are widely available.
‘This approach is valid … [but] quite painstaking, and to my knowledge very few people have used sieves to communicate coffee grind size … or to compare the performance of different grinders,’ Gagné explains.