Espresso Grinder Test Protocol: How We Test

Over the past few years, we have tested over 90 espresso grinders – from entry-level devices for €150 to professional single-dosing grinders costing over €1,000. What has emerged from this is not a gut feeling, but a structured measurement and test protocol that we have continuously refined with every test.

This article explains our procedure, why we collect these specific measurements, and what lies behind our evaluation thresholds. It also serves as a reference for all our individual grinder reviews, where we link to the corresponding sections here.

The Test Protocol at a Glance

Our test is divided into four blocks conducted at different times. This allows us to capture both a grinder's cold start and its behavior after it has been broken in and is under load.

All grinders are tested using the same coffee: Apas Espresso, a natural-processed Brazilian coffee from our partner cooperative APAS. The same coffee and the same batch of beans ensure comparability across all grinders.

Block 1 – Breaking in and initial inspection: Accessory check, grinding 1 kg of coffee, initial recipe setup, and first particle distribution samples.

Block 2 – Main measurements: Temperature, volume, grinding speed, consistency check, and further particle samples with and without RDT (Ross Droplet Technique).

Block 3 – Adjustment check: Ristretto, Lungo, returning to espresso setting – how does the grinder perform with significant changes in grind size?

Block 4 – retention: Absolute, temporary, and permanent retention are measured precisely.

Tastings take place in parallel with the respective blocks and conclude with a blind tasting.

Starting Material and Breaking In

Before taking a single measurement, we grind 1 kg of coffee through the grinder. This simulates realistic usage and ensures that the grinds and oils have settled in. A freshly unpacked grinder behaves differently than one that has already pulled 200 shots – and we test the latter.

We then check the included accessories: dosing cup, funnel, brush, and tools. 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 any other measurements are taken.

Volume

We measure the volume using a calibrated sound level meter positioned 20 cm from the grinder. Measurements are taken during a continuous grind of 250 g of coffee – not at a cold start, but during steady-state operation.

Why these thresholds? 80 dB corresponds roughly to the noise of a vacuum cleaner at a normal distance – this is the point at which a grinder is perceived as disturbing in a quiet kitchen. Anything over 90 dB, which is lawnmower territory, is simply too loud for home use. Conversely, under 80 dB – as with the Mazzer Philos at 78.1 dB – a grinder is acceptable even early in the morning or in an open-plan kitchen.

Important: The sound of grinding has two dimensions. The pure decibel figure says little about the quality of the sound. A nagging, fluctuating hum at 73 dB (as with the Varia VS3) can be subjectively more annoying than a consistent drone 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 immediately after grinding, five times in a row with 18 g each and a 20-second break in between, to visualize the heat build-up effect.

Why these thresholds? Below 30 °C, the grounds are still close to room temperature – no measurable thermal stress. From 35 °C upwards, we occasionally begin to taste differences in tastings, especially with light, aromatically delicate roasts. Anything over 39 °C, as we measured with the Zuriga G2 at 40.2 °C, is a real limitation: it disqualifies the grinder for higher throughputs because the temperature continues to rise with several consecutive shots.

Grinding Speed

Speed is measured in two different ways, which provide different information and are not directly proportionally 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 estimate whether a grinder might also be suitable for catering use.

Measurement B – Time for 18 g: For hopper grinders, this measurement is also performed with a full hopper – the value is therefore in direct proportion to the 10-second measurement. For single-dosing grinders, it is measured with an empty hopper. This also includes the time for additional bellows pumps required to fully clear the coffee. As a result, the total duration tends to be longer and is not directly comparable with hopper values.

Why is speed relevant? Very fast grinders grind with high pressure, which increases the grinding temperature. Very slow grinders increase the contact time of the coffee with the burrs – this does not have to be a weakness, but it does noticeably change the workflow. If you wait 60 seconds every morning, you will feel it.

Retention

Retention is the area inside 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 greater the retention, the more significant the taste 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 aroma climate inside the grinder. Absolute retention is the sum of both.

For the measurement, we remove all removable parts, brush out the grinder completely, and weigh the residues.

Why these thresholds? At a portion size of 18 g, 9 g of retention corresponds to almost half an espresso – half fresh, half old. You can taste that. Below 2 g, the impact on the result is minimal, provided you grind regularly. Grinders in this range – such as the Niche Zero (1.1 g) or the Varia VS3 (1.1 g) – are particularly well-suited for single dosing and for switching between different coffee varieties.

In addition, we measure the single-dosing performance: How much coffee is left behind when you input exactly 18 g and let the grinder run for 30 seconds?

Adjustment check: How consistent is the grinder?

A grinder that does not return exactly to the starting point after a major grind size adjustment is a real problem for anyone using multiple recipes or coffee varieties. We test this with a standardized sequence:

1. Espresso (starting recipe): 18 g in, 45 g out, ~25 seconds
2. Ristretto: 18 g in, 18 g out, 25 seconds
3. Lungo / Café Crème: 18 g in, 120 g out, 25 seconds
4. 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 allows us to see not only whether the grinder finds its way back, but also how the grind physically changes at very fine and very coarse settings. The deviation of the x50 value between T4 (espresso) and T7 (espresso after return) is a precise indicator of the 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 at the ZHAW (Zurich University of Applied Sciences) using a Retsch Camsizer X2 – a high-precision device for dynamic image analysis.

All samples are divided using a sample splitter to prevent separation between fine and coarse particles. Up to seven samples are measured per grinder: factory state, espresso, ristretto, lungo, return to espresso – and where possible, a slow-feeding comparison.

x50 (median particle size): The point at which 50% of the grounds are smaller and 50% larger. For espresso, this is typically 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, it has limited significance – 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 you to grind coarser to get a running shot at all. Grinders with few fines can be set significantly finer and often deliver clearer, more nuanced taste profiles.

60% Coarse Peak Width (main peak width): The size range containing 60% of the coarse particles (above 100 µm). A narrow distribution means that most particles are similar in size – consistent extraction, balanced taste. A broad distribution means heterogeneity: while some particles are already over-extracting, others lag far behind. In our tests, we have observed that as soon as the peak width rises above ~300 µm, espressos often taste "muddled" – acidity and bitterness exist disjointedly, and the sweetness is missing. We describe this in detail in the article on particle distribution.

Consistency Check

A good grinder does not just grind accurately on the first shot – it does so just as well on the fifteenth. For the consistency measurement, we grind 15 × 18 g with 30-second intervals and measure each output quantity to 0.1 g accuracy. 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 interfere with the workflow – anyone dosing to within 0.1 g 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 accurately the scale works and how it handles grind size changes.

Espresso Tasting Protocol

All the measurements in the world do not replace the decisive test: How does the espresso taste? We taste in parallel to every test phase and conduct a blind tasting at the end, where 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 precisely. We evaluate two dimensions:

Taste balance includes sweetness (balancing, shows extraction uniformity), acidity (clarity, transparency, liveliness – not sharpness), and bitterness (integrated and positive vs. harsh and disturbing).

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 rating is supplemented by a free-text description. More on this in the Espresso Tasting Protocol.

RPM Setting (Rotational Speed)

Not all grinders offer variable speed control – where available, it is treated as a separate data point in the test. The rotational speed of the burrs influences the ratio of fines to coarse particles without having to change the grind size.

At higher speeds, beans are shattered with more kinetic energy, which creates more splintering and thus more fines. At lower speeds, crushing is more controlled. The consequences in the cup are noticeable: Low RPM delivers a narrower main peak in the particle curve, clearer aromas, and more transparency – but less body. High RPM generates more fines, more body, and denser texture, but also increases the risk of uneven extraction.

The RPM setting is therefore a tool for taste control that acts independently of the grind size – especially valuable in single-dosing grinders like the DF64V, the Lagom P64, or the Varia VS6. It can help settle a fragmented extraction profile through lower speed, or create a more body-forward espresso by increasing the speed.

Example Varia VS6: The VS6 offers stepless control between 500 and 1,600 RPM. At 500 RPM, the particle curve shows a narrower main peak – the grounds are more homogeneous, the cup feels clearer. At 1,600 RPM, the peak broadens noticeably; in the espresso, more body is evident, sometimes combined with more uneven extraction. If a grinder offers an RPM setting, we document at least two settings with separate particle samples and tastings.

What the Protocol Does Not Evaluate

A good test protocol also defines its limits.

Design and haptics are not factored into the measurements. A beautifully crafted grinder does not get a points bonus from us for this – but anyone spending €1,000 can expect no plastic parts to wobble, and we note that in our observations.

Long-term performance cannot be mapped within our test framework. 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, positively surprise in this area.

All Espresso Grinders in the Test

You can find all results at a glance in our major espresso grinder comparison.