Regrinding Coffee Introduction
Effect of coffee beans addition speed to the grinder on the particle size distribution
Dear readers, thank you once again for your support and interest in my articles. I’ve been less active for a few weeks because of personal issues. Now I am back full of ideas and ready for some coffee science.
I suppose that everyone has watched the video from James Hoffmann about Regrinding coffee. If not, you can follow the link HERE. It is about the difference in coffee grind size distribution which appears as a result of the speed you use to add single-dose coffee to the grinder or grinder hopper. This is an interesting phenomenon that has some theoretical explanation. Namely that the difference is due to the time period the coffee beans spend in the grinder while grinding. Adding the beans slowly will decrease the time that a single bean spends in the grinder resulting in a hypothetical coarser grind. This could influence the coffee grinds uniformity and grinding consistency. And this is exactly what it is observed in practice. Adding the beans one by one generates a particle size distribution (shortly PSD) that is increasing the flow through the coffee puck resulting in quicker extraction time. In order to achieve the same brew time (for espresso), you must grind the coffee much finer.
* Please note, that this experiment was only about grinding whole beans and not about grinding coarser and then regrinding finer. I chose the name “Regrinding coffee” because I wanted to link that we are talking about the same topic with James Hoffmann, and my article is a kind of scientific explanation or extension to his video.
I decided to take a deeper look at what is happening when adding coffee slowly and what is the difference in the PSD compared with the standard grinding techniques.
And what is more appropriate to examine the coffee particle size than using a Lased Diffraction Particle Size Analyzer?
In parallel with the main goal – to see the difference in the PSD of coffee added slowly to the grinder compared with coffee added at once, I wanted to observe if there are additional variables that could influence this distribution. I tested four different grinders – one with conical burrs and three with flat burrs, but also tested different roasting profiles – light, medium, and dark roast. Here I’d like to give my appreciation to one of my Patrons - @blazarovbg for providing me with additional grinders and helping me collecting all the samples.
In Particle Size Analysis the most challenging part is the evaluation of the results or to extract valuable information from all the numbers that the instrument provides. Once the analysis is complete the user has a variety of approaches for reporting the results in a numerical or graphical view. Some might prefer a single number answer – what is the average size?
But in practice, a single number can’t describe the PSD of a sample.
The graphical representation is also often difficult to interpret as the differences are sometimes small to visualize but meaningful in practice. Adding the possibility that one result could be represented on a linear or logarithmic scale becomes even harder.