It's Time to Dial It Back: A (Slightly) Scientific Study on RPM

We did a bit of research into RPMs this week and how it can affect your coffee extraction, and let me tell you; I’m 90% positive there’s gotta be a “I-tried-to-read-RPM-graphs-and-survived” support group out there. But what about if you created your own graph? If you have a couple of beans and a few minutes, you too could generate your own scientific study of RPMs (and gain more appreciation for those who actually did the science-y stuff!)

Maybe the most contentious subject with coffee, many home baristas and experts alike have assessed the effects of RPM on how it’s able to deliver consistent and even extraction in coffee. I say contentious because of how different and non-conclusive much of the data is, which makes a lot of sense; people are doing tests on their own brew bar, with their specific bean and machine, and there are many variables that can interfere with getting a precise assessment (not to mention much of the research on the subject is few and far between!) 

So, with that official disclaimer, I spent my Friday afternoon doing a slightly scientific study where I tried to test out the hypothesis: does a lower RPM make coffee taste better?

Here’s the equipment I used:

Machine: ECM Synchronika (I find whenever I want an easy, reliable, “closest-to-commercial-level-machine” espresso machine)

Grinder: Turin CF64V Variable Speed Single Dose Coffee Grinder (more on this guy later)

Puck Prep tools: Pesado WDT Clump Crusher, our own branded Distribution Tool, and the Motta Spring Loaded tamper (for consistency!)

Coffee: Best I Ever Had by Gravity (literally… the best I ever had)

Here’s what I found:

Initially, I had dialed in this coffee on the setting we started the graph at, which was 1500 rpm. What was interesting to me was not only how the timing resulted in this snake-like configuration, but how wildly the taste changed.

(Note: this is getting into a vibes-based evaluation, as there was no blind tasting and each shot was tasted within 10-15 seconds after pulling.)

When I had initially dialed in this coffee, it was great! I’m quite familiar with this blend as I teach almost 90% of my coffee classes with it; the smell is like hot chocolate, the raisin and cola brightness is always incredible, and it finishes with a really nice and smooth chocolate-y feel. I did an 18g dose and pulled it in 27 seconds, which is perfect (in my opinion), on the 1400 RPM setting (I pulled a shot after with the 1500 RPM just as a test, and logged it in the chart above). With every test, I decreased the RPM by 100. 

I got nervous as the timing began to increase, and then confused when it decreased. As you would imagine, the taste began to get a bit brighter and more acidic as I was tasting, and then swung back to being bitter. Then, stuff started to turn around as soon as I reached 1100 RPM; even though the shot timing was lower than I wanted, the coffee started opening up more – not to be too poetic, but it’s almost like the volume of the coffee was turned up. Everything got a bit brighter, yet simultaneously more balanced. I wasn’t facing super harsh flavours anymore with a muddy mouthfeel as I was in the 1200-1300 range. 

Even more incredible, once I reached the lowest RPM setting, it lined up with the original dial, and the flavours really punched through, slightly more than what was originally dialed in. I’ll use the metaphor of adjusting your focus with your camera; it makes a difference when you’re 90% focused on the subject you’re taking a photo of versus 100% focused. 

Variables that can contribute to these results:

I would say some pretty key contributors to the variation (and why it’s only slightly scientific), would be with my puck prep, the human essence, and the inevitable fluctuation in temperature of the machine. 

Although I tried to keep my puck prep as consistent as possible, relying on tools like a calibrated tamper to remove as many variations as possible, I naturally spent a bit more time on my puck prep as the shot timing veered towards the 20 second mark. Hand in hand with this, the human essence influenced how I was assessing this test. If you removed the barista out of this study, I’m sure you’d have more concrete results; however, with the amount of time I had spent previous to this researching RPMs and reading the (very) common result that a lower RPM results in better espresso, I couldn’t help but get excited!

The last variation would be the temperature, which although it has a PID, there will still be small fluctuations in temperature as the boiler refills with water. Unless you have two machines that can be swapped for every test, it’s hard to get around this test. 

Final assessment:

Was it a fun test? Totally! Would the average barista be able to notice the difference? Potentially; especially if you replicated this experiment on your own time. Is it worth it? It truly depends on how expansive you’d like your espresso education to be. For an espresso geek like me, I truly enjoyed developing my palate that much more precisely and exploring a new way to make my coffee taste better beyond just experimenting with grind size (because that will only get you so far when it comes to RPMs!)

Last but not least, let’s give a shout-out to the MVP:

I couldn’t have done this study without the help of the new Turin CF64V, potentially my new BFF on the brew bar. 

I’ll explain why it’s the best by explaining what typically happens. We have seen time and time again folks (like myself) experimenting with RPMs, but using beans that are potentially a bit too dark and oily without cleaning the burrs in between. With these types of beans, it makes it especially difficult for the burrs to move through, especially with lower RPMs. So, it will clog the grinder and worst case, it will jam the grinder and leave the burrs vulnerable. Folks can then try to adjust it themselves, or have to take it in for maintenance by us. 

Due to the design of the CF64V, gravity did all the work for me. I didn’t have to worry about jamming or clogging the grinder as much as I would with other models of variable speed grinders, and I could still enjoy the power known by Turin grinders! That, plus with the ease of use and speed (thanks to a powerful motor and vertical burr set), this grinder has become much more competitive than others on the market. 

Plus, I don’t know about you, but I think it’s a pretty good-looking grinder (if you’ve been on Reddit and read some of the reviews, please join the movement #justiceforthecf64v)

What are your thoughts? Should we continue to do more slightly scientific studies? Let me know in the comments down below!

Happy Coffee-ing!