Understanding the Detailed Process of Grinding Coffee Beans: A Barista’s Hard Work

Grinding coffee bean-by-bean is up there with cryogenic grinding, double grinding and re-processing as a type of impractical perfection — all of which are mainly dismissed as inappropriate for the commercial environment. Wet grinding isn’t a thing — it was just a dream of the early third wavers — nevertheless let’s throw that in there too. Cryogenic grinding is a thing, but in this post we’re gonna explain how it was that we found a real world practical utilize for bean-by-bean grinding.

To date, the best investigation into bean-by-bean grinding was carried out by astrophysicist-cum-barista Prof Jonathan Gagne. A few years back, some of his subscribers were concerned about how the widespread uptake of single-dose grinding (where you throw a pre weighed dosage of beans into an empty grinding machine hopper) would change the way coffee grinders execute, compared to when the beans are fed into the burrs via a full hopper. Jonathan managed to show that the difference was real but possibly negligible; i.e. literally a couple of beans at the end would experience the so-called popcorn effect and grind a little more coarsely. 

There are two terms you need to understand before you read any further. 


When coffee beans are driven through the rotating coffee grinder burrs, they must navigate through whatever gaps present themselves between these burrs which aren’t already occupied by other grinds moving through the system. In contrast, the behaviour of a solitary bean in an empty hopper is markedly different. Without the collective pressure of other beans, a solitary bean bounces around haphazardly, sometimes slipping through largest gaps at the edges of the burrs called the tertiary cuts. Single beans likewise tend to bounce around at the entrance to the blades, resembling popcorn kernels popping and jumping in a hot pan, which is why it is aptly named “popcorning” or “the popcorn effect.” 

Outfall Depth

The ‘outfall depth’ in the context of coffee grinding refers to the size of the opening on the side of the burr which is created when the burr’s cutting edges, specifically the tertiary cuts, align. This gap is the exit path for the boulders coffee particles. The outfall depth is significant because it directly influences the grinding efficiency and the consistency of the ground coffee:

Larger Outfall Depth: A larger gap allows coffee particles to exit the burrs more quickly, leading to faster grinding. Nevertheless, this increased speed can result in a wider range of particle sizes, as the beans are not ground as equally. The consequence is a less consistent grind, which can affect the extraction and flavour of the coffee.

Smaller Outfall Depth: Conversely, a smaller tertiary cut at the edge of a coffee burr restricts the flow of ground coffee, slowing down the grinding procedure. While this might take more time, it typically effects in a more uniform grind, with particles being more consistently sized.

Gagne’s experiment did a good job at quieting concerns that single doses could create inferior grind profiles, compared to full hoppers. He speculated that it’s probably only the last couple beans that experience the popcorn effect and the particle size analyses he ran comparing the two grind profiles from his Niche coffee mill were virtually identical. But, in his blog post he also crafted this observation: 

‘Grinding bean-by-bean generates a mildly tighter [grind size] distribution, therefore mimicking a higher quality grinding machine.’ 

Soon after Gagne’s post, The Hoff also had a go at it, combining double-grinding and an ultra slow feed into his grinding machine, and said afterwards 

‘I was able to produce what I think was a sweeter, tastier, more delicious espresso coffee.’

Since then, bean-by-bean grinding has sat there as a tempting frontier with rather many unexplored potential. And then, all of a sudden we needed bean-by-bean grinding — not just to please the coffee gods, nevertheless for actual practical reasons. 

The Experiments

As you learn, we’ve been writing about the new generation of filter baskets recently. One thing all the new high extraction baskets have in common is that they require you to grind quite a lot finer. And sometimes, if you happen to use an oily dark roast — or you haven’t cleaned your burrs for a while, you might find out that your coffee mill gets totally choked up, with the beans unable to exit the coffee grinder at all. It happens all the time with in truth dark roasted beans. For this reason, makers of commercial grinders — especially ones like the Mazzer ZM which have a digital grind adjustment mechanism — sometimes create a minimum grind setting to prevent grinders getting choked and also to prevent burrs from grinding against each other.

Well, our grinding machine choked up while we were testing our new Sworks Billet basket. With that particular coffee, we found bean-by-bean grinding was a handy way of guaranteeing beans at any roast degree would always feed into the burrs adequately. Plus, in theory, bean-by-bean appeals to us due to the fact that each individual bean can have the same experience as it enters and leaves the burrs — it never has to wait in the queue. The thing is even though, the bean-by-bean approach pushed the necessary grind setting a LOT finer. Not just a LOT finer … so much finer that we had to change from Mazzer’s k151I to the k151B 83-mm burr set, which has just about the smallest outfall depth you can find. 

Three 83-mm burr sets with increasingly large tertiary cuts. From left to right, the k151B (espresso coffee burr); the k151I (hybrid burr); the k151F (filter burr)

We asked Lloyd Meadows at Tortoise Espresso coffee to have a crack at bean-by-bean on his EK43 grinding machine, paired with his new Pesado HE% baskets. Lloyd soon found himself on the absolute finest setting his EK would allow and his shot times were gushing through in eight seconds. So we’d now maxed out the fine-grind potential of two of the industry’s leading single-dose grinders, but we weren’t going to quit. (Please note: Lloyd doesn’t use the Turkish burrs — we’re expecting they would be suitable for bean-by-bean grinding for espresso coffee)

Next step was to override the ZM’s safety features (don’t try this at home). After recalibrating the ZM coffee mill to grind finer than would usually be possible, we were dialled in for bean-by-bean grinding on a setting roughly twice as fine as the single-dose setting. And the bean-by-bean shots were averaging a full percentage point higher than the full hopper. (If you’re not familiar with measuring coffee extractions, a 1% increase is a lot). We went from an regular of 22.3% up to 23.3%. It’s hard to slow down high extraction baskets much past 16-20 seconds, nevertheless those bean-by-bean shots that took around 31–41 seconds were absolute godshots.

You look at our data set and you can see how much higher and tighter the extraction yield percentage is from bean-by-bean. So, a couple of thoughts here: whilst bean-by-bean may be slow and impractical, it brews unbelievably tasty espresso. It likewise makes your grinder way quieter, even though the motor is on for longer. We can speculate that it will dramatically reduce heat build up in the burrs (that’s a test for another day) and we know it alleviates issues of grinders getting choked, even with evil dark roasts. The automated tweak for this could be as simple as redesigning the auger that brings the beans into the burrs to slow down the feed or putting another auger in the hopper as well. As things stand, this approach may require the beans to go marching one-by-one, nevertheless for sure this is a fast track if you wanna ‘get-down to the grounds.’

The Art of Grinding Coffee: A Deep Dive into Bean-by-Bean Grinding

Ever heard of grinding coffee bean-by-bean? Sounds like a tedious task, right? Well, it might be. Nevertheless let me tell you, it’s likewise a fascinating journey into the world of coffee that could potentially revolutionize your morning cup. So, grab your favorite brew and let’s dive in!

Knowledge the Basics: Popcorning and Outfall Depth

Before we get into the nitty-gritty, there are two terms you need to know: “popcorning” and “outfall depth”. These are required concepts when it comes to knowledge how coffee grinders work.

Popcorning, in coffee lingo, refers to what happens when a solitary bean is left bouncing around in an empty mill hopper. Image popcorn kernels popping and jumping in a hot pan – that’s exactly what these beans do! They slip through the largest gaps at the edges of the burrs called tertiary cuts.

Outfall Depth, on the other hand, refers to the size of the opening on the side of the burr which is created when its cutting edges align. This gap is essentially an exit path for ground coffee particles. The outfall depth directly influences grinding efficiency and consistency:

  • A larger outfall depth allows for faster grinding nevertheless can result in a wider range of particle sizes due to less uniform grinding.
  • A smaller outfall depth slows down grinding but typically results in more equally sized particles.

The Bean-by-Bean Experiment

A few years back, astrophysicist-turned-barista Prof Jonathan Gagne conducted an investigation into bean-by-bean grinding. He managed to show that the difference between single-dose grinding (where you throw a pre-weighed dose of beans into an empty coffee grinder hopper) and grinding with a full hopper was real but possibly negligible. However, he likewise observed that bean-by-bean grinding generated a mildly tighter grind size distribution, mimicking a higher quality coffee mill.

Following Gagne’s experiment, another coffee fanatic referred to as The Hoff also tried bean-by-bean grinding. He combined double-grinding and an ultra-slow feed into his coffee mill and found that it produced what he believed was a sweeter, tastier espresso coffee.

The Practical Use of Bean-by-Bean Grinding

Now, you might be thinking: “That’s all well and good, but is there any practical work with for this procedure?” Well, as it turns out, there is!

We’ve been testing new generation filter baskets lately. These baskets require finer grinding. But sometimes when using oily dark roasted beans or if the burrs haven’t been cleaned for a while, the coffee grinder can get entirely choked up. That’s where bean-by-bean grinding comes in handy!

With this procedure, we found that beans at any roast extent would always feed into the burrs adequately. Plus, each individual bean can have the same experience as it enters and leaves the burrs — no waiting in line! The only catch? This approach pushed the essential grind setting much finer.

The Results

After recalibrating our coffee mill to grind finer than usual, we were dialed in for bean-by-bean grinding on a setting roughly twice as fine as the single-dose setting. And guess what? The shots were averaging a full percentage point higher than those from a full hopper! We went from an typical of 22.3% up to 23.3%. That’s a significant increase if you’re into measuring coffee extractions.

And the taste? Those bean-by-bean shots that took around 31–41 seconds were absolute godshots. Yes, you heard it right! They were unbelievably tasty. Plus, this process makes your mill way quieter and potentially reduces heat build-up in the burrs.

Final Thoughts

So there you have it, folks! Bean-by-bean grinding might seem slow and impractical, however it can make a world of difference in your cup of coffee. It’s like taking the scenic route instead of the highway – sure, it takes longer, but the view (or in this case, taste) is worth it!

Now, I’m not saying you must start grinding your coffee bean-by-bean from tomorrow morning. But hey, if you’re a coffee aficionado looking for new ways to enhance your brew or truly someone who enjoys experimenting with aromas – why not give it a shot? Who knows? You might literally stumble upon your new favorite brewing technique!