In recent years, coffee grinders with adjustable RPM have become a notable innovation in the coffee world. Devices like Weber’s EG-1, Victoria Arduino’s Mythos 2, and Ceado’s Hero E37Z promise to optimize the coffee grinding process by changing the RPM settings. However, the exact effect of RPM and whether it really makes a difference is still up for debate. So, is the adjustable RPM feature a marketing ploy or a revolutionary tool in the coffee brewing process?
Grind Size Distribution: A More Uniform Holy Grail?
The ideal goal of coffee grinding is to provide more even extractions by keeping the particle size as uniform as possible. The effect of RPM on grind size distribution can vary between grinders, but the general trend is that faster RPMs tend to produce smaller particles and more fines.
Grinding Distributions at Different RPMs
Higher RPM generally produces a finer grind regardless of grind setting. This results in increased fine particles and decreased modal size distribution.
However, these effects are quite similar to those produced by changing the grind setting on the particle size distribution. For example, the median size decreases while the fine particle fraction increases. This creates uncertainty as to whether the RPM is actually changing the size distribution or simply mimicking the grind setting.
Supporting Findings
Jonathan Gagne's experiments with the Weber EG-1 show that higher RPM only makes particles finer, but makes no difference to other properties. For example, with the right grind setting, taste and extraction levels can be quite similar at different RPMs.
Extraction: RPM and Brewing Dynamics
Another way to understand the effects of RPM is to examine the extraction results obtained at different RPM settings. Gwilym Davies has shown through experiments on the Mythos 2 that lower RPM generally yields higher extraction rates.
Why Does Lower RPM Produce Higher Output?
Lower RPM produces fewer fine particles during grinding, resulting in more even dissolution and acidity.
Higher RPM can extend extraction time due to finer grinds, but can also produce a more unbalanced result in terms of extraction rate.
Dosing and RPM: The Importance of Precision
Accuracy in coffee dosing is critical, especially in busy cafes. While higher RPMs can grind coffee faster, this can often result in lower dosing accuracy. Higher-end grinders like the Mythos 2 attempt to compensate for this by lowering the RPM during the final stages of grinding.
Effect of Network Frequency and RPM on Dosing
Motors used in grinders can operate at different RPM levels depending on the mains frequency. For example, a 60 Hz mains frequency in the US will cause the same motor to operate at a higher RPM than a country using a 50 Hz mains frequency. This can create small differences in dosing accuracy.
Temperature and RPM: An Unexpected Paradox
Although it may seem that higher RPM heats up the coffee beans more, the truth is that at faster RPM, the beans are in contact with the hot surfaces of the grinder for less time. This can reduce the amount of heat produced per grind. Also, the less the motor is working, the less energy is used in the grinding process, limiting the temperature increase.
The Real Contribution of RPM to Performance
Whether RPM adjustment is a true innovation in coffee grinders or just a marketing strategy is still up for debate. However, research has shown that RPM adjustment can improve performance in the following situations:
Optimization by Brew Type: More consistent results can be achieved by adjusting the appropriate RPM for different coffee types and brewing methods.
Balance of Dosing and Speed: In high volume cafes, a system where high RPM speed provides rapid dosing, but RPM can be lowered for precise dosing, can increase productivity.
Extraction Quality: Lower RPM helps preserve coffee aroma by providing higher and more balanced extractions.
RPM is an important factor that should not be overlooked when grinding coffee. Low RPM offers more consistent results in terms of flavor and extraction, while high RPM provides speed and efficiency. Adjustable RPM grinders like the Weber EG-1, Mythos 2, and Ceado Hero provide this balance, giving coffee lovers a wide range of options.
Ultimately, optimizing RPM settings is an essential tool for anyone looking to take their coffee experience to the next level. It opens up a whole new understanding of coffee for baristas and home brewers alike.
D.EMRE KURTULUS