My goodness, the Zerno Z1 blew us away from the moment we unpacked it. So much love for detail and manufacturing has gone into this grinder – it really stands out! We have tested over 90 espresso grinders by now. The Zerno Z1 doesn't have to hide behind any other grinder and is without question one of our top favorites.
However, you pay for it! The basic version starts at around 1,200 dollars. As always, we bought the Zerno Z1 ourselves, at full price. This added up to almost 2,000 dollars in the end, including accessories, burrs, beautiful wooden trims, and the case.
That is a statement and clearly defines that we are not dealing with an entry-level grinder here, but a premium class device. Since the grinder fulfills this price point in terms of content and quality, it is not surprising that I discussed with my test colleague Michel Indelicato at the end of the test series who would get to take the grinder home until the next Home Barista Pro course.
Design and Haptics: A Massive Block
When the Zerno Z1 stands on the counter, it looks like a statement. It is surprisingly narrowly built, which we rarely see, but weighs a solid 6.5 kilograms. The massive stainless steel base carries the grinder with elegance. Zerno manages this balancing act in all facets. While other manufacturers of coffee equipment often slip into bulky, blocky design languages and martial names like “Tank” aptly summarize them, the Zerno looks more like a bird of prey. Powerful, dynamic, aesthetically elegant. The workmanship is of one piece, thought out to the last detail, and finds its climax in the grind chamber.
The 64mm burrs stand vertically in the grinder and are screwed or magnetically held from behind ("Blind Burrs"). They can be removed and changed in a few simple steps. In my view, the importance of blind burrs is still completely underestimated. We were able to comprehend it metrologically when another manufacturer switched only one burr side to blind burrs, while the burrs otherwise remained the same. Suddenly, their main peak narrowed by 30 microns!
We will come to the particle distribution of the Zerno Z1 later, but I can say this much already: The homogeneity of the Zerno Z1 is spectacular. The entire interior is built so that there is hardly any room for retention. Zerno dispenses with hard edges inside the grind chamber for this purpose. Even the sweepers have a curve and thus empty the chamber very effectively.
The grinder is modular. This allows aesthetic elements such as wooden covers to be changed, as well as technical components like the pre-breakers (augers).
Included is a massive stainless steel dosing cup that positions itself magnetically in the right place under the coffee chute.
Due to its construction, the grinder is absolutely "aligned" in its basic configuration, meaning the burrs are parallel to each other and aligned straight. To find the same grind setting again after opening the grinder and to find very well-aligned burrs, we recommend using a torque screwdriver.
The Technology: Slow, but Precise
Inside works a 300-watt motor with a permanent 900 revolutions per minute. This is rather slow compared to other grinders. We measure a grinding speed of about 1.0 to 1.1 grams per second. For a dose of 18 grams, the Zerno Z1 needs around 18 seconds to grind completely empty. That's not a speed record, but with single dosing, we are primarily concerned with quality, not time savings. The slow grinding time in conjunction with the pre-breakers used has a strong influence on the particle distribution, which, alongside the blind burrs, explains the high homogeneity of the grinds. The pre-breaker has an additional slowing effect on the grinding, reminiscent of slow feeding.
What we noticed during operation: The grinder is quite audible with a volume of around 81 decibels. Compared to whisper-quiet competitors like a Lagom P64, this stands out. It is not an unpleasant noise, but it is present.
Retention and Workflow
The topic of retention is essential for single dosing grinders. We distinguish here between temporary and permanent retention. The temporary retention – i.e., what is exchanged between two shots – is an outstanding 0.1 to 0.2 grams with the Zerno Z1. This is absolute top class and means that you get out almost exactly what you put in at the top.
We must also talk about permanent retention. This is coffee grounds that settle in cracks and corners and remain there. Here we measure about 0.6 grams, which collects mainly behind the burrs and in the chute area. This is due to the design and a good reason to clean the grinder regularly.
Some coffee collects behind the burrs in permanent retention.
Fortunately, Zerno makes it easy for us here: With just two screws on the front, the entire grind chamber can be opened. You can get to the burrs immediately, brush them out, and put everything back together. An important note for everyday use: When you screw the grinder back together, make sure to tighten the screws firmly. If you only tighten them loosely, the grind distance changes, which has direct effects on your espresso.
Depending on the bean variety, the grinder tends to have some static charge. In these cases, we recommend the Ross Droplet Technique (RDT), i.e., a small spray of water on the beans before grinding. This reduces static massively and ensures that the grinds land cleanly in the cup.
Excellent is also the grind accuracy and adjustment precision of the grinder. The grind level is indicated as a value in microns. This expresses the distance of the burrs from each other. Interestingly, the displayed grind level is relatively close to our measured x50. If we adjust the grinder to other beverages and then return to espresso, or to the noted grind setting, we get the same particle distribution within a few microns difference. Long story short: the Zerno Z1 is very well suited for switching between recipes and coffees and then returning to the original coffee.
Taste: Precision Meets Body
Let's get to the most important point: What ends up in the cup? The particle distribution measurement in the lab shows an extremely narrow main peak. The SSP High Uniformity burrs in combination with the low RPM produce very homogeneous grinds. The X50 value (the median particle size) is very close to the desired target range, which speaks for high precision.
In terms of taste, this translates into a wonderful balance. We tested our "Apas" espresso and were impressed. The espresso shows a clear structure. We taste a beautiful balance between sweetness and bitterness, with notes of nut and nougat, accompanied by a subtle but clear fruitiness. It is not an aggressive acidity, but a very integrated, bright stone fruitiness.
At the same time – and this positively surprised us – the espresso has a good body. Often, grinders with high clarity lose texture and mouthfeel. The Zerno Z1 manages the balancing act here: It delivers the differentiation of aromas without the espresso seeming thin.
However, the grinder challenges the barista. Due to the very homogeneous particle distribution, you have to grind very fine to achieve correct flow times. This means your puck preparation must be spot on. Untidy tamping or poor distribution immediately lead to channeling here. Those who work cleanly here will be rewarded with excellent results.
Interestingly, the grinder also works very well for filter coffee. If we set the grind coarse, we get a very clean, almost unimodal grind profile that enables clear and structured filter coffees. This is an exception for pure espresso grinders.
Conclusion: An Engineer's Dream with a Small Hurdle
So, who is this grinder right for? The Zerno Z1 is not a grinder for the absolute beginner who just wants a quick caffeine fix. It is a precision tool for home baristas who want to understand what burr geometry and pre-breakers do to the taste. It delivers results that play in the absolute top class.
Unlike other high-end single dosing grinders, the Zerno Z1 forgoes an option to adjust the RPM. Instead, the grinder invites you to play with different burrs and pre-breakers and delivers a grinding speed of 900 RPM tuned to the pre-breakers. In my view, this makes a lot of sense. If a company like Zerno, which deals intensively with burrs and pre-breaker geometry, develops towards a certain RPM, then a grinder can be optimized for it.
Does the filter coffee taste good? We only tested this initially and it naturally depends on the burrs used. Basically, however, we can say: yes, the filter coffee we ground and brewed with the Zerno Z1 belonged to the best filter coffees we have drunk from single dosing grinders so far.
Despite all the enthusiasm for the Zerno Z1, there is a clear "But". Zerno is a US company. For us in Europe, this means: import, customs, and above all, no local service network. If there is ever an issue with the motor, you can't just quickly send the device for repair around the corner. In the USA, this is a no-brainer; here in Europe, one must be aware of this risk. On the other hand, the grinder seems built in such a way that technical defects seem rather unlikely.
Technically and tastefully, we have nothing to criticize about the Zerno Z1, quite the opposite. It is solidly built, delivers measurably excellent results, and is fun in the workflow – if you are willing to pay the price and take the import hurdle. Anyone who already has a good grinder and is looking for that last bit of clarity and nuance will find it here. For us, it remains one of the most exciting grinders we have had on the table recently.
And who is taking the grinder home now? First of all, Michel. However, the deal isn't bad for Benjamin either. At the beginning of the year, we hope to receive our model of the Z2, and perhaps that model will then move in next to Benjamin's espresso machine...
