Behold the Hot Rod of Coffee Grinders

And you thought you were particular about how you liked your coffee.

Zerno Z1 coffee grinder sitting on counter top with several parts removed

Published April 25, 2024

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Updated April 25, 2024

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Nothing impacts the flavor of your coffee more than grind size. It’s a refrain we hear over and over again from coffee experts. Deejay Newell, co-owner (and bean ambassador) of the Montana-based Treeline Coffee Roaster, couldn’t state it any more clearly: “The size of the grind directly correlates with the amount of flavor you are extracting from the bean.”

The causal relationship between grind size and flavor may seem evident at some level. Most people understand that “making” coffee, regardless of the exact method employed, centers on extracting the flavor stored inside coffee beans into water that we can then drink.

Going one level deeper, however, is the best way to understand why machines like the Zerno Z1 – a made-in-the-USA coffee grinder offering home coffee brewers unprecedented precision and tuning abilities at a starting price of $1299 – even exist.

The Zerno Z1 is a premium and precisely engineered coffee grinder that offers an unprecedented level of customization and control.

Zerno

A crash course in coffee extraction.

What we generally think of flavors are more technically referred to as “solubles” by coffee flavor experts. And not all coffee solubles are the same.

As this incredibly helpful and detailed explanation of coffee extraction from Handground.com articulates, coffee solubles fall into four distinct compound categories, including acids & caffeine, lipids & fats, so-called Melanoidins, and finally, carbohydrates & fibers, each of which coffee drinkers associate with different flavor characteristics. Some of these flavors are good (fruit, vanilla, chocolate), while others are bad (bitters). The longer water is exposed to grinds, the more solubles will be extracted into the liquid, both good and bad.

In the coffee world, a metric known as the extraction rate is used to help quantify the ideal ratio of coffee solubles that should be extracted into a cup vs. left behind in the spent grounds. This rate is expressed as a percentage directly correlating to the coffee mass that should dissolve in water vs. stay behind.

The Specialty Coffee Association or SCAA’s optimal extraction rate target is between 18-22%, i.e., between 18 to 22% of the brewed coffee’s mass should be dissolved in the resulting liquid.

Watching this Zerno Z1 workflow video has me convinced it’d fit quite nicely into Patrick Bateman’s morning routine.

This is where precision grinding matters. It takes time for water to penetrate coffee grinds and begin extracting flavor. The smaller coffee is ground, the faster water can penetrate every part of the bean used in the brew to remove solubles.

This logic establishes the fundamental relationship between grind size and extraction time. The exact same amount of solubles can be extracted from larger-sized coffee grinds as smaller-sized grinds; the extraction process will just require more time in the case of the bigger grinds.

This ratio between grind size and extraction times creates a flavor plot of sorts that meticulous coffee brewers can explore to optimize taste. The trick is that the brewer must feel confident that all the grinds used in the brew are of equivalent size.

Inconsistently sized grinds mean that water will extract varying levels of solubles from individual grinds over the same period, preventing brewers from dialing in the flavor they intended.

The Zerno Z1 is a coffee grind tweaker’s dream.

The Zerno Z1 isn’t some set-it-and-forget-it off-the-shelf coffee grinder intended even for coffee enthusiasts looking for their daily fix.

This is a machine unabashedly designed to let obsessive home brewers endlessly tinker with grind settings to their – likely palpitating – heart’s content in a quest to learn how various grinds result in different flavor outcomes.

Although aesthetically, it’s no slouch, either.

Made of machined aircraft-grade aluminum, stainless steel, and solid wood, it exudes precision and craftsmanship, befitting its advanced capabilities.

Three burr grinder rings in copper and silver colors standing up right side by side on a grey background. — Zerno Z1 owners can opt to purchase a variety of different burr grinder sets that can easily be swapped.

Like many high-end grinders, it features a stepless adjustment knob to provide users with precision control over grind size. More interestingly, users can also swap up to five different burr grinder sets to achieve different results. And that’s just the tip of the things-you-can-fiddle-with menu.

The Zerno Z1 also features a unique engineering innovation that provides brewers precise control over the grinder feed rate. This so-called “prebreaker” does what the name implies. It cracks coffee beans before they enter the actual grind chamber.

Zerno Z1 prebreaker parts lined up in a row. — A sample of various prebreakers Zerno Z1 users can swap in and out to achieve different grind results.

As Zerno’s website explains, “controlling the rate the beans feed into the burrs prevents them from crowding the grind chamber and reduces the change of a fractional grind.” This pre-cracking process also creates more surface area on beans, which in turn allows the grinder’s burrs to “shave through the bean rather than crush them, reducing friction temperature and preventing premature brewing.”

Like the burr grinder sets, the prebreaker is also designed to be swappable, with different auger sizes providing different results. But this machine isn’t just focused on the daily grind.

Zerno Z1 buyers can also choose between four wood accent pieces to differentiate the look of their unit and even opt for a matching wood or stainless steel funnel cap and companion hard-sided carrying case, which looks both badass and slightly terrifying at the same time.

Given that it starts at $1,299 and is handmade in Chicago, no one should be surprised to learn that supplies of the Zerno Z1 are extremely limited. The brand is currently taking waitlist orders for its fourth round of deliveries, estimated to arrive in January 2025.