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Testing Manual Grinders – Flair Royal Part 1 Introduction

Different effects influencing Particle Size Distribution in manual grinders


This is a continuation of a project I started almost a year ago. In the next few months, I’ll publish a series of articles related to coffee grinding and the main idea is to better understand the physics and effects of grinding using several of the widely used manual grinders on the market. This won’t be a product review or product comparison, but every grinder will be put to a test and the results will show how they are performing. Keep in mind that the main goal is to find dependencies, effects, and correlations that are influencing the consistency and performance of the grinders. To have better statistical results several grinders will be used in this series of experiments.


The first thing I wanted to test was to transfer my previous experiment to a manual grinder. If you haven’t read my previous experiment, please follow the link HERE to learn more on the topic. It showed some remarkable results for grinders and the effect of coffee bean addition speed. It was assessed that the slow addition of the coffee to the grinder is leading to narrower distribution of the particles leading to better and more unified coffee extraction. The experiment clearly shows that better results are achieved using this approach. This difference in the performance is measurable and has a significant effect on the espresso preparation and extraction results. According to this experiment, it is always preferable to add coffee slowly for the best results. As a summary, it generates a narrower Particle Size Distribution width (Span and COV), Higher D50 (meaning coarser grind), and fewer fine particles (D10).


The previous experiment was conducted with Laser Diffraction – a powerful tool for analyzing the Particle Size Distribution (PSD) of a sample. The same instrument will be used for all future articles related to the performance of the manual grinders I’m testing. All the data will be processed because in Particle Size Analysis the most challenging part is the evaluation of the results or extracting valuable information from all the numbers that the instrument provides. Understanding PSD is a very challenging task. PSD is not just a single answer, a number, or a graph. The answer is much more complex and analyzing every part of the result could give us information about the processes happening in the grinder and later during coffee extraction.


Flair Espresso was the first company to respond to my project. After several e-mails, they send Flair Royale – a manual grinder from their portfolio. And this will be the first grinder I’ll put on the test. Two of the most important questions and the ones I’m truly interested in are:


1. Does adding the coffee little by little to the grinder influence the PSD, grinding performance, and consistency?

2. Does the speed of rotation influence the PSD, grinding performance, and consistency?

Together with these two important experiments, I’ll test how good the grinder is performing in general, but more thorough testing will be left for future experiments and articles.


Coffee addition speed has a huge impact on PSD and grinder performance when working with an electrical grinder as previously outlined. Prior to this experiment, I was thinking that coffee addition speed could have little to no effect on manual grinder because the rotation speed is very low compared to electrical. Grinding speed for an electrical grinder could vary from 350 RPM up to 1500 RPM. Using a manual grinder with a lot of effort I can achieve around 120 RPM, or 3-10 times slower. This was a premise for a lack of an effect observed in the electrical grinder caused by the coffee bean addition speed. The main explanation for this effect in an electrical grinder is the pressure that the beans entering the grinder are exerting on the particles already inside (the “pressure effect”). This could lead to additional beans cracking and fragmenting. Another proposition was made for this effect – the time the upper beans spend in the grinder being a grind. If there are many smaller particles already inside, this could cause something like a “clogging effect”, slowing the speed the coffee is passing through the grinder. This will extend the time for a single bean spending in the grinder, leading to bigger chances for the bean to be crushed to small pieces.


Both hypotheses require...


You can read the full article on my Patreon page HERE, visit www.patreon.com/npcoffeescience or click the red button below. At the price of a single espresso per month, you can read all my experiments, work-in-progress projects, future ideas, and allow me to continue my work. Thank you!





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