In recent years, we have tested over 90 espresso grinders – from entry-level devices for €150 to professional single-dosing grinders exceeding €1,000. What has emerged from this is not just a gut feeling, but a structured measurement and testing protocol that we have further developed with every test.
This article explains our process, why we collect these specific metrics, and what lies behind our evaluation thresholds. It also serves as a reference for all our individual grinder reports – where we link back to the corresponding sections here.
The Testing Protocol at a Glance
Our test is divided into four blocks, carried out at different times. This ensures that we capture both the cold start of a grinder as well as its behavior after breaking in and under load.
All grinders are tested with the same coffee: the Apas Espresso, a naturally processed Brazilian coffee from our partner cooperative APAS. Same coffee, same bean batch – this is how we create comparability across all grinders.
Block 1 – Seasoning and Initial Inspection: Accessory check, grinding 1 kg of coffee to season the burrs, initial recipe setting, first particle distribution samples.
Block 2 – Main Measurements: Temperature, noise level, grinding speed, consistency check, further particle samples with and without RDT (Ross Droplet Technique).
Block 3 – Adjustment Check: Ristretto, Lungo, returning to Espresso – how does the grinder behave during significant grind size changes?
Block 4 – Retention (Dead Space): Absolute, temporary, and permanent retention are measured exactly.
Tastings take place parallel to the respective blocks.
Raw Material and Seasoning
Before we take a single measurement, we grind 1 kg of coffee through the grinder. This simulates realistic use and ensures that coffee grounds and oils have seasoned the burrs. A freshly unboxed grinder behaves differently than one that has 100 shots under its belt – and we test the latter.
Then we check the included accessories: dosing cups, funnels, brushes, keys. We note what is included and what is missing.
For the In-Out Test, we grind 18 g of coffee three times for 30 seconds each and measure the output quantity. This gives us an initial assessment of retention and consistency – before all other measurements.
Noise Level
We measure the noise level with a calibrated sound level meter, positioned 20 cm away from the grinder. The measurement is taken during a continuous grind of 250 g of coffee – not during a cold start, but in steady-state operation.
| Rating | Decibels |
|---|---|
| Top / Quiet | below 80 dB |
| Medium / Rather loud | 80–90 dB |
| Negative / Loud | above 90 dB |
Important: The grinding tone has two dimensions. The pure decibel number says little about the quality of the noise. A penetrating, oscillating humming sound at 73 dB (like the Varia VS3) can subjectively feel more annoying than a steady hum at 78 dB. We record such qualitative impressions in our notes.
Grinding Temperature
Heat is the invisible enemy of good extraction. Coffee ground too hot loses volatile aromatic compounds even before extraction – and fats begin to oxidize. We measure the temperature of the grounds directly after grinding, five times in a row with 18 g each and a 20-second break in between, to make the heat-up effect visible.
| Rating | Temperature of grounds |
|---|---|
| Top | below 30 °C |
| Good | 30.1–35 °C |
| Medium / Warm | 35.1–39 °C |
| Negative / Very warm | above 39 °C |
Grinding Speed
Speed is measured in two different ways, which indicate different things and are not directly proportional or comparable.
Measurement A – Grams in 10 seconds (full hopper): The grinder runs with a full bean hopper. We measure how many grams are ejected in 10 seconds. This measurement is particularly relevant for grinders designed for hopper operation – it shows the maximum performance potential and helps to assess whether a grinder might also be suitable for gastronomic use.
| Rating | Grams in 10 seconds |
|---|---|
| Top | above 40 g |
| Good | 30.1–40 g |
| Medium | 20.1–30 g |
| Slow | 10–20 g |
| Very slow | below 10 g |
Measurement B – Time for 18 g: For hopper grinders, this measurement is also carried out with a full hopper – the value is therefore directly proportional to the 10-second measurement. For single-dosing grinders, it is measured with an empty hopper. Here, the time for additional pumps with the bellows, which are necessary to fully expel the coffee, is also included. The total duration is therefore tendentially longer and not directly comparable with hopper values.
| Rating | Time for 18 g |
|---|---|
| Top | 1–6 seconds |
| Good | 6.1–10 seconds |
| Medium | 10.1–15 seconds |
| Slow | 15.1–20 seconds |
| Very slow | above 20 seconds |
Retention (Dead Space)
Retention is the area in a grinder where already ground coffee remains. This coffee is not ejected immediately, but only during the next grind – it is therefore always one portion older than the freshly ground coffee. The larger the dead space, the stronger the gustatory consequences: rancid, sharp, unbalanced. We describe this in detail in our article on retention.
We distinguish between three types: Temporary retention empties and fills with every grind – it is the dominant factor for everyday quality. Permanent retention sticks permanently in crevices, around the burrs, or behind the flapper and influences the aromatic climate in the grinder. Absolute retention is the sum of both.
For the measurement, we remove all detachable parts, brush out the grinder completely, and weigh the residues.
| Rating | Absolute Retention |
|---|---|
| Very good | 0–2 g |
| Good / Low | 2.1–3.5 g |
| Medium | 3.6–5 g |
| High | 5.1–9 g |
| Very high | above 9 g |
Additionally, we measure Single-Dosing Performance: How much coffee remains when you input exactly 18 g and let the grinder run for 30 seconds?
| Rating | Deviation |
|---|---|
| Top | 0–0.15 g |
| Good | 0.16–0.3 g |
| Medium | 0.31–0.6 g |
| Poor | 0.61–1 g |
| Very poor | above 1 g |
Adjustment Check: How True is the Grinder?
A grinder that does not return exactly to the starting point after a major grind adjustment is a real problem for anyone using multiple recipes or coffee varieties. We check this with a standardized sequence:
- Espresso (Base recipe): 18 g in, 45 g out, ~25 seconds
- Ristretto: 18 g in, 18 g out, 25 seconds
- Lungo / Café Crème: 18 g in, 120 g out, 25 seconds
- Return to Espresso: 18 g in, 45 g out, 25 seconds
From each of these points, we take a 25 g sample for particle distribution measurement. This way, we see not only if the grinder finds its way back, but also how the grounds physically change at very fine and very coarse settings. The deviation of the x50 value between T4 (Espresso) and T7 (Espresso after reset) is a precise indicator of grind size repeatability.
Particle Distribution
This is the core of our scientific evaluation, and here our protocol differs from most other grinder comparisons. We analyze all samples in cooperation with the Coffee Excellence Center of the ZHAW (Zurich University of Applied Sciences) using a Retsch Camsizer X2 – a high-precision device for dynamic image analysis.
All samples are divided with a sample splitter to prevent segregation between fine and coarse particles. Up to seven samples per grinder are measured: factory state, Espresso, Ristretto, Lungo, return to Espresso – and sometimes further investigations, such as the effects of RPM adjustments or slow feeding experiments.
x50 (Median particle size): The point at which 50% of the grounds are smaller and 50% are larger. For espresso, it typically lies between 150 and 350 µm, depending on the grinder and setting. It describes the "average grind size" and shifts finer or coarser with the setting. However, on its own, its meaningfulness is limited – it describes the center, not the edges.
Fines content (Qf <100 µm): The percentage of particles smaller than 100 µm – the actual coffee dust content. A high fines content increases the body and density of an espresso but carries the risk of over-extraction and bitterness. It also forces a coarser grind setting to get a flowing shot at all. Grinders with fewer fines can be set significantly finer and often deliver clearer, more nuanced flavor profiles.
60% Coarse Peak Width (Main peak width): The size range containing 60% of the coarse particles (above 100 µm). A narrow distribution means most particles are similar in size – uniform extraction, balanced taste. A wide distribution means heterogeneity: while some particles are already over-extracting, others lag far behind. In our tests, we have observed: as soon as the peak width rises above ~300 µm, espressos often taste "scattered" – acidity and bitterness stand unconnected side-by-side, and sweetness is missing. We describe this in detail in the article on particle distribution.
Consistency Check
A good grinder doesn't just grind precisely for the first shot – it does the same for the fifteenth. For the consistency measurement, we grind 15 × 18 g with a 30-second interval and measure each output quantity to within 0.1 g. From this, we calculate the mean and standard deviation.
Standard deviations around 0.1 g are solid. Below 0.05 g is excellent. Above 0.2 g, it starts to disrupt the workflow – anyone who doses to 0.1 g precision needs a grinder that can maintain that.
For grinders with a Grind-by-Weight function (like the Eureka Libra 65 AP or the Zuriga G2 GbW), we additionally check how precisely the scale works and how it handles grind size changes.
Espresso Tasting Protocol
All the metrics in the world cannot replace the decisive test: How does the espresso taste? We taste in parallel with each test phase and conduct tastings where, at the end of a larger series of tests, all tested grinders are evaluated side-by-side.
Our tasting protocol is based on the World Barista Championship score sheet, but we have expanded the scale to 10 points and divided the attributes more discretely. We evaluate two dimensions:
- Flavor Balance includes Sweetness (balancing, shows extraction uniformity), Acidity (clarity, transparency, liveliness – not sharpness), and Bitterness (integrated and positive vs. harsh and disruptive).
- Tactile Experience includes Weight (heaviness in the mouth, independent of quality), Texture (creamy, oily, silky, dusty – the quality of the weight), and Aftertaste (length and quality after swallowing).
Each evaluation is supplemented by a free-form description. More on this in the Espresso Tasting Protocol.
RPM Setting (Rotational Speed)
Not all grinders offer variable speed control – if available, it is treated as its own data point in the test. The rotational speed of the burrs influences the ratio of fines to coarse particles without having to adjust the grind size.
At higher RPM, beans are shattered with more kinetic energy, which creates more fragmentation and thus more fines. At lower RPM, the grinding process is more controlled. The consequences in the cup are noticeable: Low RPM deliver a narrower main peak in the particle curve, clearer aromas, and more transparency – but less body. High RPM generate more fines, more body, and denser texture, but also increase the risk of uneven extraction.
The RPM setting is thus a tool for taste control that acts independently of the grind size – particularly valuable for single-dosing grinders like the DF64V, the Lagom P64, or the Varia VS6. It can help calm a frayed extraction profile through lower RPM or create a more full-bodied espresso by increasing the speed.
What the Protocol Does Not Evaluate
A good testing protocol also defines its limits.
Design and Haptics do not factor into the measurements. A beautifully crafted grinder does not get a point bonus from us – however, anyone spending €1,000 can expect that no plastic parts wobble, and we record this in the notes.
Long-term Behavior cannot be represented within our testing timeframe. Our old Mazzer grinders have been running for 15+ years – that is experiential knowledge, not a test result.
Filter Coffee is only tested where a grinder is explicitly marketed as All-Purpose. Some grinders, like the Eureka Libra 65 AP, surprise us positively in this regard.
All Espresso Grinders in the Test
You can find all results at a glance in our large espresso grinder comparison.
