Coffee Data Science

Coffee Feed Control with the Momentem Grinder

Looking at the top burr as one to control flow to the bottom burr

6 min readFeb 2, 2024

The Momentem grinder finally arrived at my door, and I was so excited. This grinder is a rare dual burr coffee grinder, and it is the first dual burr hand grinder. My first tests are to get to the right grind setting for espresso, which turns out to be a little more challenging due to the two burrs until I realized that the top burr could be used to slow feed the bottom burr. Let’s take a look.

Momentem Grinder

The grinder is unique for a few reasons:

Dual burr
Chaff collector
Sieve at the bottom.

Chaff doesn’t taste too good, and this idea is very interesting. There is not as much chaff collected in the espresso use-case, but for pour-over, I suspect the impact is larger.

Two burrs allow for some feed control as the first one can slowly feed the second one.

The grinder itself is heavy, but it feels solid and a good design.

Grind Size

Previous experience shows slow feeding the beans to a grinder changes the particle distribution and how the shot flows. The effects the full pile of beans on the burrs also changes the particle distribution throughout the grind as the pressure from the bean pile decreases.

In trying to understand how two burrs affects the grind, feed rate was a confounding variable. If the top burr grinds too coarse, everything went to the bottom burr, and the top burr acted like a pre-breaker. If the top burr grinds too fine, then there is a challenge getting some of the finer grinds into the bottom burr.

I used the DiFluid Omni to analyze particles of both burrs, and I started with a few settings for the top. There were some similarities, but some odd shifts when the particles got large. This could have been conflated by the sample size being a few 100 particles.

Refining this measurement to between 0 and 900 um, the lower setting on Top has a much bigger impact relative to the 3 and 4 settings.

I took the top setting at 3 and I looked at a few settings across the bottom. These follow what one would expect as the burr gap decreases, finer particles are made.

If I change the top setting, it is not quite apparent how it affects the final grind distribution. I did not analyze particle shape which is also impacted by two burrs.

Looking at the Top at 3 by itself and then the Bottom at 2, the impact on distribution is as expected. I plotted this out of interest.

I found through dialing in my grind that the top setting at 2.5, and the bottom at 2 was more optimal.

I then turned to some paired shots to understand performance.

Metrics of Performance

I used two sets of metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.

Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.

Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).

Intensity Radius (IR) is defined as the radius from the origin on a control chart for TDS vs EY, so IR = sqrt( TDS² + EY²). This metric helps normalize shot performance across output yield or brew ratio.

Data

All performance numbers should be taken with the caveat that the Zerno burrs were seasoned and the Momentem burrs were not. They could change taste and profile over time after around 5 kg, which means about 200 shots (at 24g) for my use. This will take about few months at my current use rate because I use it half the time. So far, I have pulled 40 shots with the Momentem.

I compared the Momentem grinder to the Zerno grinder across 14 shots from 9 roasts. From the scatter plot, TDS and EY seemed a little less, but not always.

Zooming in, there are a lot of cases on the line.

For taste, Momentem was close to Zerno but still under performing.

In terms of individual taste metrics, the surprising one seems to be an improvement on bitterness, but I’m unsure if this is significant.

From the general statistics, TDS was close to being statistically significant but not quite. Rich and Syrup as taste metrics were, but the others were not.

Momentem effectively works on par with Zerno, which is great for a grinder as portable as Momentem. I have been pulling a few staccato shots using the sieve in the bottom. I have been very impressed by the grinder, and I continue to use it a few times a week for espresso.

Disclaimer: I am friends with Micky at Momentem, and I would love to say there isn’t bias, but bias is part of life. If I didn’t like the grinder, I wouldn’t have said much publicly, so often the bias is what is not said instead of what is said.

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